Identification of Genes Encoding Granule-Bound Starch Synthase Involved in Amylose Metabolism in Banana Fruit

Abstract

Granule-bound starch synthase (GBSS) is responsible for amylose synthesis, but the role of GBSS genes and their encoded proteins remains poorly understood in banana. In this study, amylose content and GBSS activity gradually increased during development of the banana fruit, and decreased during storage of the mature fruit. GBSS protein in banana starch granules was approximately 55.0 kDa. The protein was up-regulated expression during development while it was down-regulated expression during storage. Six genes, designated as MaGBSSI-1, MaGBSSI-2, MaGBSSI-3, MaGBSSI-4, MaGBSSII-1, and MaGBSSII-2, were cloned and characterized from banana fruit. Among the six genes, the expression pattern of MaGBSSI-3 was the most consistent with the changes in amylose content, GBSS enzyme activity, GBSS protein levels, and the quantity or size of starch granules in banana fruit. These results suggest that MaGBSSI-3 might regulate amylose metabolism by affecting the variation of GBSS levels and the quantity or size of starch granules in banana fruit during development or storage.

Soluble Starch Synthase III-1 in Amylopectin Metabolism of Banana Fruit: Characterization, Expression, Enzyme Activity, and Functional Analyses

“…For natural ripening treatment, banana samples were kept at 22°C and allowed to ripen in open air. In accordance with the previously published banana ripening stages (Miao et al, 2014), fruits stored for 0, 5, 10, 15, 20, 25, and 30 days period of post-harvest (DPH) were frozen in liquid nitrogen and stored at -80°C until starch/amylopectin quantification, mRNA and protein expression analysis.…”

“…The supernatant was then transferred to a 20 mL volumetric flask. The total starch, amylose, and amylopectin contents of the extract were determined following Yang et al (1992) and Miao et al (2014). The amylopectin content was calculated by subtracting the amylose content from the total starch content.…”

“…Current research on banana starch has mainly focused on granule structure (Low et al, 2015) and antioxidant capacities (Sarawong et al, 2014), as well as physicochemical properties of starch (Zhang and Hamaker, 2012; Utrilla-Coello et al, 2014). Several key genes involved in starch biosynthesis or conversion of starch to sucrose have been isolated and characterized in banana, including MaGBSSI (Miao et al, 2014), DBE (Bierhals et al, 2004), SUCROSE PHOSPHATE SYNTHASE ( SPS ), SUCROSE SYNTHASE ( SuSy ), and INVERTASE (Hubbard et al, 1990). However, to our knowledge, the function of SS genes has not been characterized in banana.…”

Lineage-Specific Evolutionary Histories and Regulation of Major Starch Metabolism Genes during Banana Ripening

“…The MaSS4 and MaSS9 genes encoding SSIV enzymes were also expressed based on RNA-Seq data ( Figure 9A ) albeit at very low levels. This could be due to the role of SSIV in starch granule initiation that occurs at earlier stages in banana fruit development (Roldan et al, 2007; Crumpton-Taylor et al, 2013; Miao et al, 2014). …”

“…In addition, GBSS might also be involved in the synthesis of extra-long unit chains of amylopectin (Hanashiro et al, 2008). A recent study has proposed six banana GBSS genes classified in two sub-groups (Miao et al, 2014). Our phylogenetic analysis confirmed the four members of the first sub-group as GBSS genes whereas the two remaining genes corresponded to the soluble SSII genes MaSS5 and MaSS8 .…”