Polygalacturonase inhibiting protein enhances cell wall strength of strawberry fruit for resistance to Botrytis cinerea infection

Polygalacturonase inhibitor protein (PGIP) plays an active role in resisting pathogens from degrading cell walls. Strawberry fruit quality is strongly affected by Botrytis cinerea (B. cinerea), so PGIP genes from heterologous species were cloned and analyzed to identify genes having good B.cinerea infection resistance. In this study, a PGIP gene from grape fruit was isolated and heterologously transiently expressed in strawberry fruit. The results revealed that VvPGIP (PGIPO) overexpression in strawberry fruit led to B. cinerea infection resistance, but RNA interference of VvPGIP (PGIPI) made fruit susceptible to B. cinerea infection. qPCR indicated that expression levels of FaPGIP was increased after transient expression of VvPGIP in PGIPO fruit for 48 h as compared to the control and that polygalacturonase enzyme (PG) was significantly down-regulated, whereas PGIPI fruit had the opposite effect, suggesting that VvPGIP may activate the FaPGIP expression levels, thereby reducing the disease incidence and index of strawberry fruits and improving the disease resistance of the fruits. VvPGIP also inhibited the decrease of total pectin and cellulose content. Transcriptome and metabolome results showed that PGIP is widely involved in photosynthesis, signal transduction, and secondary metabolism of fruits. In addition, many enzyme activities and defense reaction were also significantly enriched. Using Y2H and BiFC technology, we screened and verified the interaction protein of VvPGIP with Endo-1, 3-Beta-Glucanase (VvGLU) and pathogen-related protein 4 (VvPR-4) on the cell membrane. Taken together, PGIP as a key protein in plant defense response functions a key role in regulating the strength of cell walls and can inhibit the degradation of plant cell walls by pathogens.