Comparative transcriptome analysis reveals an ABA-responsive regulation network associated with cell wall organization and oxidation reduction in sugar beet

Abstract

Abscisic acid (ABA) is an essential phytohormone and plays a key role in root architecture and plant stress responses. However, the ABA signalling pathway and its regulatory network in sugar beet roots remain unclear. Here, we carried out a time course experiment and performed global transcriptome profiling via strand-specific RNA sequencing (ssRNA-seq) to evaluate the response of sugar beet plants to exogenous ABA. According to the expression patterns of 5625 differentially expressed transcription units (TUs), the ABA-responsive stages within 24 h were divided into the early (1 h), intermediate (6 h and 12 h) and late (24 h) stages. Gene Ontology (GO) analysis revealed that oxidation reduction (GO: 0055114) and cell wall organization (GO: 0071555) were enriched in all ABA-responsive stages. For oxidation reduction, genes encoding cytochromes, peroxidases (PODs) and 2-oxoglutarate and Fe(II)-dependent oxygenases (2OG-Fe(II)s) constituted the largest proportion. ABA-responsive xyloglucan endotransglucosylase/hydrolase (XTH), expansin A (EXPA), pectinesterase (PME), pectate lyase (PL) and cellulose synthase (CES) were also detected in terms of cell wall organization. By performing regulation prediction and co-expression analysis, we determined that three genes, one encoding an AP2 domain-containing transcription factor (TF) and two encoding Dof domain-containing TFs (BVRB_4g074790, BVRB_8g180860 and BVRB_9g211370, respectively) may play an important role in the regulation of oxidation reduction and cell wall organization. Our profiling of ABA-responsive genes provides valuable information for understanding the molecular functions of regulatory genes and will aid in the future molecular breeding of sugar beet.