Increased soluble sugar accumulation in postharvest peaches in response to different defense priming elicitors

A so-called priming defense is activated only when a plant suffers from heavy pathogenic invasion, thus avoiding excessive energy and material costs under low pathogen loads. In our previous studies, we demonstrated that elicitors, such as beta-aminobutyric acid (BABA), methyl jasmonate (MeJA) or benzothiadiazole (BTH), can induce the priming of a defense response against fungal infections in postharvest peach fruit. Interestingly, the defense priming was accompanied by increased soluble sugar accumulation. In this study, we aimed to elucidate the mechanism underlying the increase in sugar contents in primed peach fruit. We identified a group IIa WRKY transcription factor, PpWRKY40, from Prunus persica. Using yeast one-hybrid assays, electrophoretic mobility shift assays and dual-luciferase reporter assays, we show that PpWRKY40 is a transcriptional activator of the sucrose synthesis-related genes sucrose synthase (PpSS1) and sucrose-phosphate synthase (PpSPS3). Induction of defense priming with BABA, MeJA or BTH upregulated PpWRKY40 expression and promoted the transcript levels of PpSS1 and PpSPS3 and their enzymatic activities in postharvest peach fruit, resulting in the enhancement of sucrose synthesis. Moreover, the activities of sorbitol catabolizing enzymes-S6PDH, NAD(+)-SDH, NADP(+)-SDH-increased in the peach fruit treated with the defense priming elicitors, indicating that sorbitol was converted into glucose and fructose. Induction of defense priming also improved the sensory quality and antioxidant levels of fruit. In summary, the three defense priming elicitors improved the soluble sugar accumulation and overall quality in postharvest peach by upregulating the PpWRKY40 gene and increasing sorbitol catabolism.

Automated summary

A defense priming mechanism is activated in plants only under heavy pathogenic invasion, reducing energy and material costs under low pathogen loads. In this study, the researchers discovered that the expression of PpWRKY40, a transcription factor, is increased by defense priming elicitors such as BABA, MeJA or BTH, leading to the upregulation of sucrose synthesis-related genes and increased sugar accumulation in postharvest peach fruit. Additionally, the activities of sorbitol catabolizing enzymes also increased, converting sorbitol into glucose and fructose. This defense priming mechanism improved the overall quality and antioxidant levels of the fruit.