Identif ication of a hypersensitive response core peptide of HrpZ and its role in increasing grape downy mildew resistance

Harpins play a key role in inducing disease resistance in crops,and identifying their core functional regions and establishing a system for their efficient expression would be very valuable.In this study,large amounts of soluble fusion proteins of harpin HrpZ and its subpeptides were obtained via the optimized induction conditions(28℃ with 0.5 mmol·L^(-1) IPTG for 6 h)in Escherichia coli BL21(DE3).Hypersensitive response(HR)assays demonstrated that the C-terminal 66 aa of HrpZ(HrpZ_C_2_2)elicited a strong HR in tobacco(Nicotiana benthamiana)and grape(Flame Seedless)leaves.Additionally,treatment with HrpZ,and particularly HrpZ_C_2_2,significantly reduced the disease incidence and severity index of field vine leaves and those inoculated with downy mildew.The determination of the physiological parameters indicated that HrpZ,and especially HrpZ_C_2_2,improved the photosynthesis-and chlorophyll fluorescence-related parameters,enhanced the activity of defense-related enzymes,including SOD,POD,CAT and PAL,and increased the H_(2)O_(2) level.Collectively,we efficiently expressed a core peptide of HrpZ and elucidated its strong ability to elicit a HR and resistance to downy mildew.This research provides insight into understanding the structure and function of HrpZ and will advance the application of HrpZ_C_2_2 to increase the resistance of grapevine to downy mildew.

VvMYB14 participates in melatonin-induced proanthocyanidin biosynthesis by upregulating expression of VvMYBPA1 and VvMYBPA2 in grape seeds

This work demonstrated that melatonin increases continuously in seeds,particularly seed coats,during berry ripening.Exogenous melatonin treatments significantly increased the proanthocyanidin(PA)content,partially through ethylene signaling,in seed coats.VvMYB14 expression exhibited patterns similar to melatonin accumulation over time,which was largely induced by melatonin treatment in seed coats during berry ripening.Additionally,VvMYB14 bound to the MBS element of the VvMYBPA1 promoter to activate expression.VvMYB14 overexpression largely upregulated expression of VvMYBPA1,VvMYBPA2 and VvLAR1 and increased the PA content in grape seed-derived calli.Similar increases in AtTT2 and AtBAN expression and PA content were found in VvMYB14-overexpressing Arabidopsis seeds.It was also observed that VvMYB14 overexpression increased ethylene production and thereby induced expression of VvERF104,which bound to the ERF element of the VvMYBPA2 promoter and activated its expression.Additionally,VvERF104 suppression reduced the VvMYB14 overexpression-induced increases in expression of VvMYBPA2 and VvLAR1 and PA content.Further experiments revealed that melatonin-induced increases in the expression of VvMYBPA1,VvMYBPA2,VvERF104 and VvLAR1 and PA accumulation were significantly reduced in VvMYB14-suppressing grape calli and leaves.Collectively,VvMYB14 mediates melatonin-induced PA biosynthesis by directly transactivating VvMYBPA1 expression and indirectly upregulating VvMYBPA2 expression via VvERF104.