CaWRKY6 Alleviates The Antagonistic Effect Of High Temperature And High Humidity On Resistance To Ralstonia Solanacearum In Pepper(Capsicum Annuum)

The combination of high temperature and high humidity(HTHH)can cause serious diseases in plants by depressing the resistance response to soil-borne pathogens.Solanaceae,such as pepper and tobacco,are especially susceptible to these effects.This selection pressure contributed to the evolution of countermeasures that attenuate plant sensitivity to disease under HTHH,but the underlying mechanisms are poorly understood.Herein,we identified and characterized a Capsicum annuum WRKY transcription factor,designated CaWRKY6,as a novel regulator that attenuates the HTHH-induced depression of resistance to Ralstonia solanacearum.CaWRKY6 belongs to subgroup ?b,is upregulated by HTHH and/or Ralstonia solanacearum inoculation and by application of exogenous jasmonic acid(JA),ethylene(ET),or abscisic acid(ABA).Overexpression of CaWRKY6 conferred greater thermotolerance under 100%humidity,and increased resistance to R.solanacearum in inoculated leaves but not in systemic leaves.When challenged simultaneously with HTHH and R solanacearum,Companied with upregulation of hypersensitive-response marker genes(e.g.,HIN1),genes involved in JA,ET and ABA signaling,genes involved in thermotolerance and active oxygen scavenging.By contrast,CaWRKY6-silenced pepper plants displayed susceptibility to R.solanacearum inoculation and/or HTHH.Our data also showed CaWRKY6 acts upstream CaWRKY40,a regulator in pepper response to HTHH and R.solanacearum infection.These results suggest that CaWRKY6 attenuates the antagonistic effect of HTHH on resistance to R.solanacearum attack in pepper plants.