J Plant Biotechnol 2020; 47(3): 194-202
Published online September 30, 2020
https://doi.org/10.5010/JPB.2020.47.3.194
© The Korean Society of Plant Biotechnology
Correspondence to : e-mail: pgel2006@gmail.com
This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
The sweetpotatoes (Ipomoea batatas) generate adventitious roots (ARs) from cut stems that develop into storage roots and make for an important means of propagation. However, few studies have investigated the hormones involved in AR development in sweetpotato. In this study, the expression patterns of hormone-related genes involved in AR formation were identified using the transcriptome data. RNA-seq data from stems grown for 0 and 3 days after cutting were analyzed. In addition, hormone-related genes were identified among differentially expressed genes (DEGs) and filtered genes, and cluster analysis was used to characterize expression patterns by function. Most hormone-related regulated genes expressed 3 days after growing the cut stems were abscisic acid (ABA)- related genes, followed by ethylene- and auxin-related genes. For ABA, the biosynthesis genes (including genes annotated to NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3)) and signal transduction and perception genes (including genes annotated to PROTEIN PHOSPHATASE 2Cs (PP2Cs)) tended to decrease. Expression patterns of auxin- and ethylene-related genes differed by function. These results suggest that ABA, auxin, and ethylene genes are involved in AR formation and that they may be regulated in a hormone function-dependent manner. These results contribute to the identification of hormone functions during AR formation and may contribute to understanding the mechanism of AR formation in the sweetpotato.
Keywords Ipomoea batatas, Sweetpotato, Adventitious root, Transcriptome, Hormone
Adventitious roots (AR) are formed during normal development and produced in response to stresses (e.g., flooding, nutrient deprivation, wounding). In addition, AR formation from cutting stems is carried out for horticultural plant propagation (Bellini et al. 2014; Steffens and Rasmussen 2016). AR formation is triggered by external signals or intrinsic hormone, and occurs in cells neighboring vascular tissues. This development mechanism was elucidated by data accumulated from various plants such as
AR formation by sweetpotatoes is physiologically and economically important as it affects the development of storage roots, and thus, continues to be a topic of interest. Villordon et al. (2012) found that ethylene inhibitor treatment (1-methylcyclopropene) reduced AR count and length, and Deng et al. (2012) confirmed that AR formation was induced by H2O2 and inhibited by ABA. Ma et al. (2015) revealed a relationship between stem node number and AR formation, and presented the morphologies AR development and emergence as observed under an optical microscope. In addition, Kim et al. (2020) performed RNA-seq analysis using stems cuttings to identify the transcriptome involved in AR formation by sweetpotatoes.
The mechanism of AR formation is highly complex and involves external factors and intrinsic signals, and hormone is one of the important component of the latter. However, research on AR formation by sweetpotatoes has been limited, and thus, little is known of hormonal regulation during the process. Therefore, in this study, we investigated the regulation of hormone-related genes involved in AR formation through RNA-seq data obtained from the stem cuttings of sweetpotato (Bioproject: PRJNA610478, SRA: SRR11241425, SRR11241427) (Kim et al. 2020). The genes annotated with hormone-related genes were divided by function, and their expression patterns during AR formation were clustered. These results indicate the hormones involved in AR formation and their regulation at the transcriptional level.
Sweetpotato (cv. Annouimo) stems were cut at lengths of ~30 cm, and ~12 cm sections were planted in pot and grown for 0 or 3 days in a growth chamber at 25 ± 3°C under a 16 h light/8 h dark diurnal cycle to promote AR formation. The samples were prepared for RNA-seq in duplicate from ~12cm cut stem sections planted in pot while growing for 0 or 3 days. Total RNA was extracted from cutting stems by using a modified CTAB method, and treated with DNase I (Takara Bio, Japan) to remove genomic DNA (Kim and Hamada 2005). RNA sequencing was performed as previously described Kim et al. (2020).
Differentially expressed genes (DEGs) (≥ 2-fold) or filtered genes (minimum number of transcripts ≥100, E-value of annotation ≤ 10-5, identity of annotation ≥ 60) were selected to investigate the regulation of hormone-related genes during AR formation. DEGs were used to determine dramatically regulated hormones during AR formation, and filtered genes were used to investigate the comprehensive regulation of genes by function among the hormones selected by DEGs regulation.
First, hormone-response genes among DEGs were identified using Gene Ontology (GO) terms such as “response to auxin”, “response to brassinosteroid” in The Arabidopsis Information Resource (TAIR, http://www.arabidopsis.org/) (The Gene Ontology Consortium 2019). DEGs related to hormone functions (e.g., biosynthesis, signal transduction) were also identified. The following studies were used to select each hormone-related genes from DEGs : Auxin (Kim et al. 2018; Ljung 2013; Winkler et al. 2017), Brassinosteroids (Chung and Choe 2013; Clouse 2011), Gibberellins (Sun 2008), Cytokinins (Kieber and Schaller 2014), ABA (Fujita et al. 2009; Hauser et al. 2011; Hauser et al. 2017; Kwak et al. 2002; Nambara and Marion-poll 2005; Schweighofer et al. 2004; Yoshida et al. 2015), Ethylene (Guo and Ecker 2004; Schaller and Kieber 2002; Yoo et al. 2009), Jasmonates (Acosta and Farmer 2010; Wasternack and Hause 2013), Salicylic acid (Dempsey et al. 2011; Seyfferth and Tsuda 2014).
Second, in order to investigate the regulations of hormone-related genes by function during AR formation, filtered genes were selected and were divided by function based on the studies mentioned above. The hierarchical cluster analysis of filtered genes were performed by using cluster 3.0 (http://bonsai.hgc.jp/~mdehoon/software/cluster/software) (de Hoon et al. 2004), and heatmap was visualized by Java Treeview (http://jtreeview.sourceforge.net/) (Saldanha 2004) software.
We performed transcriptome analysis on data obtained from cuttings stems grown for 0 and 3 days to investigate the hormones involved in AR formation. The RNA-seq showed 42,459 representative transcripts and 2,092 DEGs including genes involved in single-organism metabolic process, cell periphery, and the biosynthesis of secondary metabolites (Kim et al. 2020). Hormone-related genes were selected from DEGs (≥ 2-fold change) and their regulations were confirmed (Fig. 1).
First, genes corresponding to each hormone response gene as indicated by the GO terms “response to auxin” and “response to BR” among DEGs were examined to identify the hormones involved in AR formation. The number of regulated hormone response genes was the highest for ABA, followed by auxin and ethylene. Genes annotated to ‘response to ABA’ were more likely to decrease (68 genes) than increase (33 genes). On the other hand, more genes annotated to ‘response to auxin’ (up: 20 genes, down: 9 genes) and ‘response to ethylene’ (up: 12 genes, down: 7 genes) were up-regulated. In addition, the ratios of regulated genes among genes corresponding to each GO term were calculated to investigate the regulation of these hormones during AR formation in more detail. We found 23.5 % (101 genes) of 430 genes corresponding to the GO term ‘response to ABA’ were regulated more than 2-fold.
Second, the studies on the hormone-related genes mentioned in Materials and Methods were used to investigate the number of genes corresponding to biosynthesis and signal transduction pathways among DEGs. ABA biosynthesis and signal transduction genes were most regulated, and ethylene, auxin, and JA were also regulated. Ratios of regulated genes to total hormone-related genes showed trends similar to numbers of regulated genes. Among the regulated genes, ABA biosynthesis and signal transduction genes were down-regulated (Table 1). To investigate the regulations of ABA, auxin, ethylene, which involve many genes during AR formation, cluster analysis was performed by hormone function.
Table 1 Regulated hormone-related genes during adventitious root formation in sweetpotato. Regulated biosynthesis and signal transduction genes of each hormone were identified
Hormone | Regulation | No. gene | |
---|---|---|---|
Auxin | Up | 3 | I.bat1SL031281t004 ( |
Down | 5 | I.bat1SL027550t003 ( | |
BRs | Up | 2 | I.bat1SL012835t007 ( |
Down | 0 | ||
CKs | Up | 1 | I.bat1SL014914t003 ( |
Down | 0 | ||
ABA | Up | 1 | I.bat1SL007169t001 ( |
Down | 12 | I.bat1SL003385t003 ( | |
Ethylene | Up | 6 | I.bat1SL025381t002 ( |
Down | 3 | I.bat1SL007764t002 ( | |
JAs | Up | 3 | I.bat1SL006234t006 ( |
Down | 2 | I.bat1SL012217t002 ( |
BRs, brassinosteroids; CKs, cytokinins; ABA, abscisic acid; JAs, jasmonates
Filtered genes were represented by a heatmap to investigate the expression patterns of hormone-related genes by function. ABA-related gene expressions were generally lower in stems grown for 3 days (Fig. 2), particularly, those of ABA biosynthesis and signal transduction associated genes. For ABA synthesis-related genes, NCED3 annotated genes I.bat1SL011651t022 and I.bat1SL002093t019, which play important roles in the biosynthesis of ABA, were down- regulated. For signal transduction-related genes, down-regulations were more dramatic than up-regulations. Notably, the expressions of PP2Cs (
The three genes involved in auxin biosynthesis were annotated, but no gene was significantly regulated during AR formation (data not shown). On the other hand, other genes (metabolism, early response, and transporter genes) were found to be regulated (Fig. 3). DIOXYGENASE FOR AUXIN OXIDATION 1 (
During AR formation, many ethylene-related genes were regulated, and more genes were down-regulated than up- regulated (Fig. 4). Regarding ethylene biosynthesis-related genes, genes annotated to 1-AMINO-CYCLOPROPANE-1- CARBOXYLIC ACID OXIDASE (ACO) were more regulated than the genes annotated to 1-AMINO-CYCLOPROPANE-1- CARBOXYLATE SYNTHASE (ACS). In particular,
During AR formation, regulatory mechanisms in nucleus among ethylene signal transduction genes were down-regulated, and these are the nuclear transcription activator ETHYLENE- INSENSITIVE3 (
Sweetpotatoes form ARs from stem cuttings and develop fibrous or storage roots. Since root development by sweetpotatoes directly affects productivity, several studies have addressed the subject. Recently, transcriptome analyses have been performed on sweetpotatoes at various developmental stages (Dong et al. 2019; Zhang et al. 2017). The other analysis have compared
During AR formation, ABA-related genes were significantly down-regulated, and the expressions auxin- and ethylene- related genes were regulated. Other hormone-related genes were also regulated, but to lesser extents. These results differ from hormone regulations observed during storage root development. For example, cytokinin expression increases during the development of tuberous roots from sweetpotato fibrous roots, and the initial expressions level of ABA- and auxin- related genes are known to increase and then decrease again during the process (Dong et al. 2019). Other hormones have been reported to exhibit developmental level dependent expressional pattern changes (Nakatani and Komeichi 1991; Noh et al. 2010; Tanaka et al. 2008). The present study indicates that ABA, auxin, and ethylene are probably involved in the AR formation by sweetpotatoes, but unfortunately, we did not determine details regarding their functions or crosstalk.
In order to examine the regulatory mechanisms of hormones during AR formation, hormone-related genes were classified into biosynthesis, signal transduction, metabolism, or transporter genes. The most prominent change observed in 3-day grown stems was the down-regulation of ABA biosynthesis genes and signal transduction genes (Fig. 2 and 5).
As described above, ABA was regulated at the transcription level by biosynthesis and signal transduction factors. Furthermore, these results suggest that AR formation may be induced by the down-regulation of ABA. Although Nakatani and Komeichi (1991) indicated that ABA acts on the vascular cambium of storage roots during the development of sweetpotato roots, the function of ABA during AR formation from cuttings may differ. Several studies on various plants have suggested that ABA affects AR formation. Dawood et al. (2016) showed that in
Auxin is known to be involved in cell dedifferentiation and AR emergence through a metabolism, transport, and early response gene (
Finally, it was found that ethylene also regulated the biosynthesis- and signal transduction-related genes (Fig. 4). Ethylene is known to induce epidermal cell death by H2O2 during AR formation in other plants (Steffens et al. 2006; Steffens and Sauter 2005; Steffens and Sauter 2009). Since ABA and GA have been known to be involved in this process, it would be interesting to investigate ethylene function during AR formation by sweetpotatoes and its effects on crosstalk between ABA and GA.
The AR formation of sweetpotatoes from cuttings is important, but the mechanism involved has not been elucidated. Hormone-related genes selected from RNA-seq analysis, which was performed to characterize the DEGs during AR formation by sweetpotato, were represented as heatmap by their functions. We found that ABA, auxin, and ethylene related genes were regulated during AR formation in different directions, presumably in a function dependent-manner. It would be interesting to know the functions of these hormones through further researches.
The authors have no conflict of interest to declare.
This study was funded by Project no. 117039-3 from Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries (iPET), Ministry of Agriculture, Food and Rural Affairs
J Plant Biotechnol 2020; 47(3): 194-202
Published online September 30, 2020 https://doi.org/10.5010/JPB.2020.47.3.194
Copyright © The Korean Society of Plant Biotechnology.
Hualin Nie ・Sujung Kim・Yongjae Lee ・Hyungjun Park ・Jeongeun Lee ・Jiseong Kim・Doyeon Kim・ Sunhyung Kim
Department of Environmental Horticulture, University of Seoul, Seoul 02504, Republic of Korea
Interdisciplinary Graduate School of Agriculture and Engineering, University of Miyazaki, Japan
Correspondence to:e-mail: pgel2006@gmail.com
This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
The sweetpotatoes (Ipomoea batatas) generate adventitious roots (ARs) from cut stems that develop into storage roots and make for an important means of propagation. However, few studies have investigated the hormones involved in AR development in sweetpotato. In this study, the expression patterns of hormone-related genes involved in AR formation were identified using the transcriptome data. RNA-seq data from stems grown for 0 and 3 days after cutting were analyzed. In addition, hormone-related genes were identified among differentially expressed genes (DEGs) and filtered genes, and cluster analysis was used to characterize expression patterns by function. Most hormone-related regulated genes expressed 3 days after growing the cut stems were abscisic acid (ABA)- related genes, followed by ethylene- and auxin-related genes. For ABA, the biosynthesis genes (including genes annotated to NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3)) and signal transduction and perception genes (including genes annotated to PROTEIN PHOSPHATASE 2Cs (PP2Cs)) tended to decrease. Expression patterns of auxin- and ethylene-related genes differed by function. These results suggest that ABA, auxin, and ethylene genes are involved in AR formation and that they may be regulated in a hormone function-dependent manner. These results contribute to the identification of hormone functions during AR formation and may contribute to understanding the mechanism of AR formation in the sweetpotato.
Keywords: Ipomoea batatas, Sweetpotato, Adventitious root, Transcriptome, Hormone
Adventitious roots (AR) are formed during normal development and produced in response to stresses (e.g., flooding, nutrient deprivation, wounding). In addition, AR formation from cutting stems is carried out for horticultural plant propagation (Bellini et al. 2014; Steffens and Rasmussen 2016). AR formation is triggered by external signals or intrinsic hormone, and occurs in cells neighboring vascular tissues. This development mechanism was elucidated by data accumulated from various plants such as
AR formation by sweetpotatoes is physiologically and economically important as it affects the development of storage roots, and thus, continues to be a topic of interest. Villordon et al. (2012) found that ethylene inhibitor treatment (1-methylcyclopropene) reduced AR count and length, and Deng et al. (2012) confirmed that AR formation was induced by H2O2 and inhibited by ABA. Ma et al. (2015) revealed a relationship between stem node number and AR formation, and presented the morphologies AR development and emergence as observed under an optical microscope. In addition, Kim et al. (2020) performed RNA-seq analysis using stems cuttings to identify the transcriptome involved in AR formation by sweetpotatoes.
The mechanism of AR formation is highly complex and involves external factors and intrinsic signals, and hormone is one of the important component of the latter. However, research on AR formation by sweetpotatoes has been limited, and thus, little is known of hormonal regulation during the process. Therefore, in this study, we investigated the regulation of hormone-related genes involved in AR formation through RNA-seq data obtained from the stem cuttings of sweetpotato (Bioproject: PRJNA610478, SRA: SRR11241425, SRR11241427) (Kim et al. 2020). The genes annotated with hormone-related genes were divided by function, and their expression patterns during AR formation were clustered. These results indicate the hormones involved in AR formation and their regulation at the transcriptional level.
Sweetpotato (cv. Annouimo) stems were cut at lengths of ~30 cm, and ~12 cm sections were planted in pot and grown for 0 or 3 days in a growth chamber at 25 ± 3°C under a 16 h light/8 h dark diurnal cycle to promote AR formation. The samples were prepared for RNA-seq in duplicate from ~12cm cut stem sections planted in pot while growing for 0 or 3 days. Total RNA was extracted from cutting stems by using a modified CTAB method, and treated with DNase I (Takara Bio, Japan) to remove genomic DNA (Kim and Hamada 2005). RNA sequencing was performed as previously described Kim et al. (2020).
Differentially expressed genes (DEGs) (≥ 2-fold) or filtered genes (minimum number of transcripts ≥100, E-value of annotation ≤ 10-5, identity of annotation ≥ 60) were selected to investigate the regulation of hormone-related genes during AR formation. DEGs were used to determine dramatically regulated hormones during AR formation, and filtered genes were used to investigate the comprehensive regulation of genes by function among the hormones selected by DEGs regulation.
First, hormone-response genes among DEGs were identified using Gene Ontology (GO) terms such as “response to auxin”, “response to brassinosteroid” in The Arabidopsis Information Resource (TAIR, http://www.arabidopsis.org/) (The Gene Ontology Consortium 2019). DEGs related to hormone functions (e.g., biosynthesis, signal transduction) were also identified. The following studies were used to select each hormone-related genes from DEGs : Auxin (Kim et al. 2018; Ljung 2013; Winkler et al. 2017), Brassinosteroids (Chung and Choe 2013; Clouse 2011), Gibberellins (Sun 2008), Cytokinins (Kieber and Schaller 2014), ABA (Fujita et al. 2009; Hauser et al. 2011; Hauser et al. 2017; Kwak et al. 2002; Nambara and Marion-poll 2005; Schweighofer et al. 2004; Yoshida et al. 2015), Ethylene (Guo and Ecker 2004; Schaller and Kieber 2002; Yoo et al. 2009), Jasmonates (Acosta and Farmer 2010; Wasternack and Hause 2013), Salicylic acid (Dempsey et al. 2011; Seyfferth and Tsuda 2014).
Second, in order to investigate the regulations of hormone-related genes by function during AR formation, filtered genes were selected and were divided by function based on the studies mentioned above. The hierarchical cluster analysis of filtered genes were performed by using cluster 3.0 (http://bonsai.hgc.jp/~mdehoon/software/cluster/software) (de Hoon et al. 2004), and heatmap was visualized by Java Treeview (http://jtreeview.sourceforge.net/) (Saldanha 2004) software.
We performed transcriptome analysis on data obtained from cuttings stems grown for 0 and 3 days to investigate the hormones involved in AR formation. The RNA-seq showed 42,459 representative transcripts and 2,092 DEGs including genes involved in single-organism metabolic process, cell periphery, and the biosynthesis of secondary metabolites (Kim et al. 2020). Hormone-related genes were selected from DEGs (≥ 2-fold change) and their regulations were confirmed (Fig. 1).
First, genes corresponding to each hormone response gene as indicated by the GO terms “response to auxin” and “response to BR” among DEGs were examined to identify the hormones involved in AR formation. The number of regulated hormone response genes was the highest for ABA, followed by auxin and ethylene. Genes annotated to ‘response to ABA’ were more likely to decrease (68 genes) than increase (33 genes). On the other hand, more genes annotated to ‘response to auxin’ (up: 20 genes, down: 9 genes) and ‘response to ethylene’ (up: 12 genes, down: 7 genes) were up-regulated. In addition, the ratios of regulated genes among genes corresponding to each GO term were calculated to investigate the regulation of these hormones during AR formation in more detail. We found 23.5 % (101 genes) of 430 genes corresponding to the GO term ‘response to ABA’ were regulated more than 2-fold.
Second, the studies on the hormone-related genes mentioned in Materials and Methods were used to investigate the number of genes corresponding to biosynthesis and signal transduction pathways among DEGs. ABA biosynthesis and signal transduction genes were most regulated, and ethylene, auxin, and JA were also regulated. Ratios of regulated genes to total hormone-related genes showed trends similar to numbers of regulated genes. Among the regulated genes, ABA biosynthesis and signal transduction genes were down-regulated (Table 1). To investigate the regulations of ABA, auxin, ethylene, which involve many genes during AR formation, cluster analysis was performed by hormone function.
Table 1 . Regulated hormone-related genes during adventitious root formation in sweetpotato. Regulated biosynthesis and signal transduction genes of each hormone were identified.
Hormone | Regulation | No. gene | |
---|---|---|---|
Auxin | Up | 3 | I.bat1SL031281t004 ( |
Down | 5 | I.bat1SL027550t003 ( | |
BRs | Up | 2 | I.bat1SL012835t007 ( |
Down | 0 | ||
CKs | Up | 1 | I.bat1SL014914t003 ( |
Down | 0 | ||
ABA | Up | 1 | I.bat1SL007169t001 ( |
Down | 12 | I.bat1SL003385t003 ( | |
Ethylene | Up | 6 | I.bat1SL025381t002 ( |
Down | 3 | I.bat1SL007764t002 ( | |
JAs | Up | 3 | I.bat1SL006234t006 ( |
Down | 2 | I.bat1SL012217t002 ( |
BRs, brassinosteroids; CKs, cytokinins; ABA, abscisic acid; JAs, jasmonates.
Filtered genes were represented by a heatmap to investigate the expression patterns of hormone-related genes by function. ABA-related gene expressions were generally lower in stems grown for 3 days (Fig. 2), particularly, those of ABA biosynthesis and signal transduction associated genes. For ABA synthesis-related genes, NCED3 annotated genes I.bat1SL011651t022 and I.bat1SL002093t019, which play important roles in the biosynthesis of ABA, were down- regulated. For signal transduction-related genes, down-regulations were more dramatic than up-regulations. Notably, the expressions of PP2Cs (
The three genes involved in auxin biosynthesis were annotated, but no gene was significantly regulated during AR formation (data not shown). On the other hand, other genes (metabolism, early response, and transporter genes) were found to be regulated (Fig. 3). DIOXYGENASE FOR AUXIN OXIDATION 1 (
During AR formation, many ethylene-related genes were regulated, and more genes were down-regulated than up- regulated (Fig. 4). Regarding ethylene biosynthesis-related genes, genes annotated to 1-AMINO-CYCLOPROPANE-1- CARBOXYLIC ACID OXIDASE (ACO) were more regulated than the genes annotated to 1-AMINO-CYCLOPROPANE-1- CARBOXYLATE SYNTHASE (ACS). In particular,
During AR formation, regulatory mechanisms in nucleus among ethylene signal transduction genes were down-regulated, and these are the nuclear transcription activator ETHYLENE- INSENSITIVE3 (
Sweetpotatoes form ARs from stem cuttings and develop fibrous or storage roots. Since root development by sweetpotatoes directly affects productivity, several studies have addressed the subject. Recently, transcriptome analyses have been performed on sweetpotatoes at various developmental stages (Dong et al. 2019; Zhang et al. 2017). The other analysis have compared
During AR formation, ABA-related genes were significantly down-regulated, and the expressions auxin- and ethylene- related genes were regulated. Other hormone-related genes were also regulated, but to lesser extents. These results differ from hormone regulations observed during storage root development. For example, cytokinin expression increases during the development of tuberous roots from sweetpotato fibrous roots, and the initial expressions level of ABA- and auxin- related genes are known to increase and then decrease again during the process (Dong et al. 2019). Other hormones have been reported to exhibit developmental level dependent expressional pattern changes (Nakatani and Komeichi 1991; Noh et al. 2010; Tanaka et al. 2008). The present study indicates that ABA, auxin, and ethylene are probably involved in the AR formation by sweetpotatoes, but unfortunately, we did not determine details regarding their functions or crosstalk.
In order to examine the regulatory mechanisms of hormones during AR formation, hormone-related genes were classified into biosynthesis, signal transduction, metabolism, or transporter genes. The most prominent change observed in 3-day grown stems was the down-regulation of ABA biosynthesis genes and signal transduction genes (Fig. 2 and 5).
As described above, ABA was regulated at the transcription level by biosynthesis and signal transduction factors. Furthermore, these results suggest that AR formation may be induced by the down-regulation of ABA. Although Nakatani and Komeichi (1991) indicated that ABA acts on the vascular cambium of storage roots during the development of sweetpotato roots, the function of ABA during AR formation from cuttings may differ. Several studies on various plants have suggested that ABA affects AR formation. Dawood et al. (2016) showed that in
Auxin is known to be involved in cell dedifferentiation and AR emergence through a metabolism, transport, and early response gene (
Finally, it was found that ethylene also regulated the biosynthesis- and signal transduction-related genes (Fig. 4). Ethylene is known to induce epidermal cell death by H2O2 during AR formation in other plants (Steffens et al. 2006; Steffens and Sauter 2005; Steffens and Sauter 2009). Since ABA and GA have been known to be involved in this process, it would be interesting to investigate ethylene function during AR formation by sweetpotatoes and its effects on crosstalk between ABA and GA.
The AR formation of sweetpotatoes from cuttings is important, but the mechanism involved has not been elucidated. Hormone-related genes selected from RNA-seq analysis, which was performed to characterize the DEGs during AR formation by sweetpotato, were represented as heatmap by their functions. We found that ABA, auxin, and ethylene related genes were regulated during AR formation in different directions, presumably in a function dependent-manner. It would be interesting to know the functions of these hormones through further researches.
The authors have no conflict of interest to declare.
This study was funded by Project no. 117039-3 from Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries (iPET), Ministry of Agriculture, Food and Rural Affairs
Table 1 . Regulated hormone-related genes during adventitious root formation in sweetpotato. Regulated biosynthesis and signal transduction genes of each hormone were identified.
Hormone | Regulation | No. gene | |
---|---|---|---|
Auxin | Up | 3 | I.bat1SL031281t004 ( |
Down | 5 | I.bat1SL027550t003 ( | |
BRs | Up | 2 | I.bat1SL012835t007 ( |
Down | 0 | ||
CKs | Up | 1 | I.bat1SL014914t003 ( |
Down | 0 | ||
ABA | Up | 1 | I.bat1SL007169t001 ( |
Down | 12 | I.bat1SL003385t003 ( | |
Ethylene | Up | 6 | I.bat1SL025381t002 ( |
Down | 3 | I.bat1SL007764t002 ( | |
JAs | Up | 3 | I.bat1SL006234t006 ( |
Down | 2 | I.bat1SL012217t002 ( |
BRs, brassinosteroids; CKs, cytokinins; ABA, abscisic acid; JAs, jasmonates.
Shin Woo Lee·Yun-Hee Kim
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