PbrWRKY42-PbrSOT13 module regulated sorbitol accumulation in the developing ‘Yali’ fruit after three-layer-paper bagging treatment

As a conventional preharvest handling practice, fruit bagging could control insects and diseases, and therefore improve the visual quality of pear, but suppress the accumulation of soluble sugar. However, the molecular mechanism underlying this phenomenon has not been fully elucidated until recently. In this study, the three-layer-paper bagging treatment considerably suppressed the accumulation of four soluble sugars in the developing 'Yali' fruit. In combination with the expression profiles of the differently expressed sugar-metabolism-related genes, PbrSOT13, encoding a plasma membrane-located protein, was selected and confirmed to participate in sorbitol influx and accumulation in pear. Notably, molecular dynamic simulation indicated that the Asp52 and Arg132 residues were pivotal in this process. After a conjoined analysis of cis-acting elements in PbrSOT13 promoter and the expression profiles of transcription factors, PbrWRKY42 was identified as a candidate upstream regulator of PbrSOT13. The nuclear PbrWRKY42 could bind to the W-box element of PbrSOT13 promoter and then activate its transcription, as evidenced by yeast one-hybrid assay and dual-luciferase assay, thus enhancing sorbitol accumulation in fruit. Further study found that the transcription of PbrSOT13 and PbrWRKY42 was suppressed by the elevated temperature and the reduced light-exposure period, which was the consequence of bagging treatment. Taken together, our results implied that three-layer-paper bagging treatment would alter temperature and light exposure around the developing 'Yali' fruit, and thus suppress sorbitol accumulation via the PbrWRKY42-PbrSOT13 module.