A- and B-subgenome characterisation of sucrose synthase family proteins and functional identification of MaSUS2.2 reveals its involvement in the starch accumulation in banana fruit

Abstract

ABSTRACT Sucrose synthase (SUS) is one of the most important enzymes catalysing the synthesis and cleavage of sucrose, and it also plays a crucial role in multiple plant biological processes. However, SUS has been scarcely reported in banana which accumulates large amounts of starch in its fruit. In this genome-wide study on banana, nine SUS genes were identified in each of the two subgenomes (A and B) for the first time, which were clustered into three distinct groups. Those in the group II underwent further duplications. In the transcriptome analysis of Baxijiao (BX, AAA) and Fenjiao (FJ, ABB) banana, four MaSUSs (MaSUS-2.1, -2.2, -2.3, and -3.2) and five MbSUSs (MbSUS-2.1, -2.2, -2.3, -2.4, and -3.2) were expressed during fruit development, with MaSUS2.2/MbSUS2.2 being the most highly expressed. Transient overexpression of MaSUS2.2 resulted in a significant increase in its transcription, which was consistent with significantly enhanced starch content in banana fruits. Its function was further identified by its transient silencing expression in banana fruit discs, which led to a significant reduction in total starch content. Taken together, the results show that multiple SUS genes, especially SUS2.2, play an important role in starch accumulation in banana fruit.