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

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.

KEYWORDS:

• Banana
• sucrose synthase
• SUS
• subgenome characterisation
• sucrose biosynthesis
• starch biosynthesis
• fruit development

Acknowledgments

Z.-Q.J. and B.-Y.X. conceived and designed the experiments. D.-F.Z., H.-X.M., P.-G.S., Q.L., C.-H.J., J.-Y.W., J.-B.Z., Z.W., and J.-H.L. performed the experiments and carried out the analysis. H.-X.M., P.-G.S., and Q.L. wrote the manuscript. All authors discussed the results and approved the final manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Key R&D Program of China [grant number 2019YFD100200], the Hainan Provincial Natural Science Foundation of China [grant numbers 319MS091, 321RC636, 321RC638, and 2019CXTD412], the Central Public-interest Scientific Institution Basal Research Fund [grant numbers 1630052020002, 1630052017010, and 1630052020006], the National Natural Science Foundation of China [grant number 32172545], and the Modern Agro-industry Technology Research System [grant number CARS-31].