Involvement of CsWRKY70 in salicylic acid-induced citrus fruit resistance against Penicillium digitatum

Penicillium digitatum causes serious losses in postharvest citrus fruit.Exogenous salicylic acid(SA)can induce fruit resistance against various pathogens,but the mechanism remains unclear.Herein,a transcriptome-based approach was used to investigate the underlying mechanism of SA-induced citrus fruit resistance against P.digitatum.We found that CsWRKY70 and genes related to methyl salicylate(MeSA)biosynthesis(salicylate carboxymethyltransferase,SAMT)were induced by exogenous SA.Moreover,significant MeSA accumulation was detected in the SA-treated citrus fruit.The potential involvement of CsWRKY70 in regulating CsSAMT expression in citrus fruit was studied.Subcellular localization,dual luciferase,and electrophoretic mobility shift assays and an analysis of transient expression in fruit peel revealed that the nucleus‐localized transcriptional activator CsWRKY70 can activate the CsSAMT promoter by recognizing the W-box element.Taken together,the findings from this study offer new insights into the transcriptional regulatory mechanism of exogenous SA-induced disease resistance in Citrus sinensis fruit.

Alteration of pectin metabolism in blood orange fruit(Citrus sinensis cv.Tarocco)in response to vesicle collapse

Segment drying is a severe physiological disorder of citrus fruit,and vesicles become granulated or collapsed.Aside from the hypothesis that alteration of cell wall metabolism is the main factor of citrus granulation,little is known about vesicle collapse.This study aimed to elucidate the changes in pectin metabolism during vesicle collapse in blood orange.Vesicle collapse was characterized by decreased nutrients and increased chelate-and sodium carbonate-soluble pectin and calcium content.The nanostructure of chelate-soluble pectin became complex and developed multi-branching upon collapse.The activity of pectin methylesterase increased,while that of polygalacturonase and pectate lyase decreased upon collapse.Genome-wide transcriptional analysis revealed an increasing pattern of genes encoding pectin methylesterase and other enzymes involved in pectin synthesis and demethylesterification upon collapse.Drying vesicles were characterized by increased abscisic acid content and relevant gene expression.In conclusion,we discovered alteration in pectin metabolism underlying citrus vesicle collapse,mainly promoting pectin demethylesterification,remodeling pectin structures,and further inhibiting pectin degradation,which was hypothesized to be a main factor for citrus collapse.This is the first study to disclose the potential intrinsic mechanism underlying vesicle collapse in orange fruit.