Genome-wide analyses of SWEET family proteins reveal involvement in fruit development and abiotic/biotic stress responses in banana

Sugars Will Eventually be Exported Transporters (SWEET) are a novel type of sugar transporter that plays crucial roles in multiple biological processes. From banana, for the first time, 25 SWEET genes which could be classified into four subfamilies were identified. Majority of MaSWEETs in each subfamily shared similar gene structures and conserved motifs. Comprehensive transcriptomic analysis of two banana genotypes revealed differential expression patterns of MaSWEETs in different tissues, at various stages of fruit development and ripening, and in response to abiotic and biotic stresses. More than 80% MaSWEETs were highly expressed in BaXi Jiao (BX, Musa acuminata AAA group, cv. Cavendish), in sharp contrast to Fen Jiao (FJ, M. acuminata AAB group) when pseudostem was first emerged. However, MaSWEETs in FJ showed elevated expression under cold, drought, salt, and fungal disease stresses, but not in BX. Interaction networks and co-expression assays further revealed that MaSWEET-mediated networks participate in fruit development signaling and abiotic/biotic stresses, which was strongly activated during early stage of fruit development in BX. This study provides new insights into the complex transcriptional regulation of SWEETs, as well as numerous candidate genes that promote early sugar transport to improve fruit quality and enhance stress resistance in banana.