Molecular identification of the key starch branching enzyme-encoding gene SBE2.3 and its interacting transcription factors in banana fruits

Abstract

Starch branching enzyme (SBE) has rarely been studied in common starchy banana fruits. For the first time, we report here the molecular characterization of seven SBE (MaSBE) and six SBE (MbSBE) genes in the banana A-and B-genomes, respectively, which could be classified into three distinct subfamilies according to genome-wide identification. Systematic transcriptomic analysis revealed that six MaSBEs and six MbSBEs were expressed in the developing banana fruits of two different genotypes, BaXi Jiao (BX, AAA) and Fen Jiao (FJ, AAB), among which MaSBE2.3 and MbSBE2.3 were highly expressed. Transient silencing of MaSBE2.3 expression in banana fruit discs led to a significant decrease in its transcription, which coincides with significant reductions in total starch and amylopectin contents compared to those of empty vector controls. The suggested functional role of MaSBE2.3 in banana fruit development was corroborated by its transient overexpression in banana fruit discs, which led to significant enhancements in total starch and amylopectin contents. A number of transcription factors, including three auxin response factors (ARF2/12/24) and two MYBs (MYB3/308), that interact with the MaSBE2.3 promoter were identified by yeast one-hybrid library assays. Among these ARFs and MYBs, MaARF2/MaMYB308 and MaARF12/MaARF24/MaMYB3 were demonstrated via a luciferase reporter system to upregulate and downregulate the expression of MaSBE2.3, respectively.

Starch branching enzymes as putative determinants of postharvest quality in horticultural crops

“…Thus, the AP/AM ratio increased dramatically during ripening, in concert with the increase in soluble sugar content and fruit color change from green to red [ 169 ]. This phenomenon where the proportion of amylopectin increases relative to amylose, was also evident in ripening apple and banana [ 64 , 173 ]. It is possible to speculate that of the available starch left during fruit ripening, the amylose, or long-chained amylopectin was converted into amylopectin whose branch-like structure has a much higher susceptibility to enzyme attack, allowing the rapid process of starch degradation into soluble sugars and supply for respiration.…”

“…1 B). In addition, banana contains at least four types of SBE2, and transcripts corresponding to these SBE2s have been identified, indicating that they are expressed [ 64 ].…”

“…Hormones, such as abscisic acid (ABA), ethylene, salicylic acid (SA), jasmonic acid (MeJA), and sugar signals have been reported to regulate SBE activity in cereal and horticulture crops [ 81 – 83 ]. In addition, transcription factors (TFs) that belong to the WRKY, MYB, bZIP, AP2/EREBP families, may bind to their cognate cis-elements in the 5′ upstream regions of SBEs to activate or suppress transcription [ 64 , 84 – 86 ]. However, information on the transcriptional regulations of SBE is fragmented, and putative hub genes or master regulators have not been identified [ 87 ].…”

“…Relative expression level of apple SBE genes (MdSBE2.1, MD12G1020600; MdSBE2.2, MD14G1017700; MdSBE3, MD08G1002300) were retrieved from AppleMDO [ 172 ], the starch and sugar data were adapted from two publications [ 173 , 174 ]. Banana starch and SBEs profiles were summarized from three publications [ 64 , 161 , 175 ]. TSS – Total soluble solids.…”

Overexpression of a Banana Aquaporin Gene MaPIP1;1 Enhances Tolerance to Multiple Abiotic Stresses in Transgenic Banana and Analysis of Its Interacting Transcription Factors

“…Drought, salt, and cold stresses can disrupt the osmotic balance of plants. To cope with these stresses, there will be some accumulation of related substances in plants ( Miao et al, 2020 ); proline and soluble sugar accumulation is extensive. The accumulation of these substances protects the cells by reducing the osmotic pressure of the cells in the plant ( El-Esawi et al, 2019 ).…”