Apple SERRATE negatively mediates drought resistance by regulating MdMYB88 and MdMYB124 and microRNA biogenesis

The function of serrate(SE)in miRNA biogenesis in Arabidopsis is well elucidated,whereas its role in plant drought resistance is largely unknown.In this study,we report that MdSE acts as a negative regulator of apple(Malus×domestica)drought resistance by regulating the expression levels of MdMYB88 and MdMYB124 and miRNAs,including mdm-miR156,mdm-miR166,mdm-miR172,mdm-miR319,and mdm-miR399.MdSE interacts with MdMYB88 and MdMYB124,two positive regulators of apple drought resistance.MdSE decreases the transcript and protein levels of MdMYB88 and MdMYB124,which directly regulate the expression of MdNCED3,a key enzyme in abscisic acid(ABA)biosynthesis.Furthermore,MdSE is enriched in the same region of the MdNECD3 promoter where MdMYB88/MdMYB124 binds.Consistently,MdSE RNAi transgenic plants are more sensitive to ABA-induced stomatal closure,whereas MdSE OE plants are less sensitive.In addition,under drought stress,MdSE is responsible for the biogenesis of mdm-miR399,a negative regulator of drought resistance,and negatively regulates miRNAs,including mdm-miR156,mdm-miR166,mdm-miR172,and mdm-miR319,which are positive regulators of drought resistance.Taken together,by revealing the negative role of MdSE,our results broaden our understanding of the apple drought response and provide a candidate gene for apple drought improvement through molecular breeding.

APPLE SUMO E3 REGULATES LIGASE MDSIZ1 NEGATIVELY DROUGHT TOLERANCE

Drought stress typically causes heavy losses in apple production and uncovering the mechanisms by which apple tolerates drought stress is important in apple breeding.MdSIZl is a SUMO(small ubiquitin-like modifier)E3 ligase that promotes SUMO binding to substrate proteins.Here,we demonstrate that MdSIZl in apple has a negative relationship with drought tolerance.MdSIZ1 RNAi transgenic apple trees had a higher survival rate after drought stress.During drought stress they had higher leaf water potential,reduced ion leakage,lower H_(2)O_(2)and malondialdehyde contents,and higher catalase activity.In addition,MdSIZl RNAi transgenic plants had a higher net photosynthetic rate during the latter period of drought stress.Finally,the transgenic apple trees also altered expression levels of some microRNAs in response to drought stress.Taken together,these results indicate that apple MdSIZl negatively regulates drought stress by enhancing leaf water-holding capacity and antioxidant enzyme activity.

APPLE SUMO E3 LIGASE MDSIZ1 NEGATIVELY REGULATES DROUGHT TOLERANCE

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