Interfering small ubiquitin modifiers(SUMO)improves the thermotolerance of apple by facilitating the activity of MdDREB2A

Heat stress,which is caused by global warming,threatens crops yield and quality across the world.As a kind of post-translation modification,SUMOylation involves in plants heat stress response with a rapid and wide pattern.Here,we identified small ubiquitin modifiers(SUMO),which affect drought tolerance in apple,also participated in thermotolerance.Six isoforms of SUMOs located on six chromosomes in apple genome,and all the SUMOs were up-regulated in response to heat stress condition.The MdSUMO2 RNAi transgenic apple plants exhibited higher survival rate,lower ion leakage,higher catalase(CAT)activity,and Malondialdehyde(MDA)content under heat stress.MdDREB2A,the substrate of MdSUMO2 in apple,was accumulated in MdSUMO2 RNAi transgenic plants than the wild type GL-3 at the protein level in response to heat stress treatment.Further,the inhibited SUMOylation level of MdDREB2A in MdSUMO2 RNAi plants might repress its ubiquitination,too.The accumulated MdDREB2A in MdSUMO2 RNAi plants further induced heat-responsive genes expression to strengthen plants thermotolerance,including MdHSFA3,MdHSP26.5,MdHSP18.2,MdHSP70,MdCYP18-1 and MdTLP1.In summary,these findings illustrate that interfering small ubiquitin modifiers(SUMO)in apple improves plants thermotolerance,partly by facilitating the stability and activity of MdDREB2A.

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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