Identification, expression analysis, and functional characterization of salt stress‐responsive genes of AP2/ERF transcription factors in sweetpotato

Abstract

The AP2/ERF transcription factors (TFs) regulate various processes of plant growth, development, and response to environmental stimuli. Although they have been extensively documented in many plants, little is known about stress responsive APETALA2/ethylene response factor (AP2/ERF) genes in sweetpotato (Ipomoea batatas L.). In this study, 20 putative AP2/ERF genes, named IbERF1, IbERF2, and IbERF5–IbERF23 were identified based on the salt‐treated RNA‐seq data from two sweetpotato cultivars with different salt tolerance. Phylogenetic analysis and sequence characterization identified that all the screened IbERF proteins contained a conserved AP2 domain, which belonged to dehydration‐responsive element binding proteins (DREB; 7 members) or ERF (13 members) subfamily. The systematic expression analysis of 12 mainly salt‐induced IbERFs by quantitative real‐time polymerase chain reaction (qRT‐PCR) revealed that most IbERFs were remarkably increased by multiple abiotic stresses, such as NaCl, dehydration, and cold stress. Furthermore, varying degrees of upregulation were also detected in the expression of most IbERFs when treated with hormone abscisic acid, jasmonic acid, and salicylic acid. The expression profiles of IbERFs corroborate their involvement in diverse biological processes. In addition, the IbERF5, which was exclusively upregulated by the treatments, was identified as a nuclear protein without transcriptional activation activity. Collectively, the data of stress responsive IbERFs will provide valuable knowledge for further functional studies of IbERFs in sweetpotato stress tolerance.

Genome-wide identification, phylogeny and expression analysis of AP2/ERF transcription factors family in sweet potato

“…1 ). There were 172 genes assigned to the ERF subfamily, which contains one single AP2 domain, and all these genes can be subdivided into two groups: DREB [A1 (4), A2 (10), A3 (1), A4 (15), A5 (14), A6 (11)] and ERF [B1 (38), B2 (20), B3 (40), B4 (5), B5 (4), B6 (10)], which is consistent with a previous report [ 25 ] (Table S2 ). The AP2 subfamily had 21 genes with two AP2 DNA binding domains.…”

“…In particular, the expression of g25316 , which encodes the IbDREB1/IbCBF3 protein, showed a remarkable reduction under cold stress and a significant increase under drought stress, which is consistent with a previous study [ 41 , 43 ]; and the function of its homologue AtCBF3 in Arabidopsis [ 76 ], further confirming the reliability of our results. IbERF1 ( g35249 ) and IbERF7 ( g55038 ) was induced by salt stress, which is in accordance with a previous report [ 25 , 42 ]. Moreover, IbRAP2–12 ( g60949 ) showed increased patterns under both drought and salt stress, which is similar to published results [ 22 ].…”

“…In addition, a previous report showed that AtERF113 ( RAP2.6 L ) can be activated by drought and salt stress, and enhance the tolerance to these stressors in Arabidopsis [ 77 ]. Our results found that the homologous genes of AtERF113 in the sweet potato, including g28064 , g60059 and g52248 , showed similar expression patterns to those in a previous report [ 25 ], indicating that these genes may play similar roles in the sweet potato stress response. Based on the above data, we speculated that cis -elements might be crucial regulatory factors for the spatial and temporal expression of IbAP2/ERF genes, which could form a complex regulatory network with other functional proteins during development and stress response processes [ 78 ].…”

“…For abiotic treatments, sweet potato seedlings were incubated in quarter-strength Hoagland solution in a greenhouse (16 h/8 h of light/dark, 30 °C/22 °C day/night). The treatment assays were conducted as described in a previous report [ 25 ] with some modifications. Cold stress was performed by culturing seedlings at 4 °C, and the roots were collected.…”

“…Extensive studies have been conducted to investigate the significant roles of AP2/ERF genes in regulating diverse developmental processes, stress responses and plant hormone signal transduction, including ethylene, auxin, salicylic acid and jasmonic acid [ 12 – 14 ]. Several members of the ERF subfamily have been revealed as viable candidates to enhance plant abiotic stress tolerance and display different response patterns under abiotic stress, including cold ( AtCBF1 , PtERF109 ) [ 15 , 16 ], heat ( ZmDREB2A , AtDREB1A ) [ 17 , 18 ], osmotic stress ( CkDREB ) [ 19 ], drought ( OsDREB1 , IbRAP2–12 ) [ 20 – 22 ], and high-salt stress ( CaDREBLP1 , LkERF-B2, IbERF5 ) [ 23 – 25 ]. Members of the AP2 subfamily play vital roles in the regulation of organ architecture and development, such as floral organ patterning [ 26 – 28 ], leaf development [ 29 ] and embryo development [ 30 ], while RAV subfamily genes are the main factors involved in plant hormone signal transduction [ 31 ], including that of brassinosteroids [ 32 ], ethylene [ 33 ] and auxin [ 34 ], and are the main regulators of multiple stress responses [ 11 , 35 , 36 ].…”