Expression Profiling Of OsWRKY42 And Its Function In Xa21-mediated Resistance To Xanthomonas Oryzae Pv.oryzae

Rice(Oryza sativa L.)is one of the most important crops and the model organism in basic research for plants.WRKY is one of the largest transcription factor families in rice,which is involved in rice growth and development,as well as response to abiotic and biotic stresses.Previous studies found that OsWRKY42 protein expression increased during interaction between rice and Xanthomonas oryzae pv.oryzae(Xoo),which provide a clue for OsWRKY42 to play a role in the resistance response of rice to Xoo.In this study,Western blot(WB)were used to study the expression profiling of OsWRKY42 protein during rice growth and development,abiotic stress,exogenous hormone treatment and Xoo inoculation processes.It was found that the expression of OsWRKY42 protein was tissue-and spatiotemporal-specific during rice growth,but it was expressed constantly in rice leaves.Treatment of abiotic stresses such as cold,heat,drought,salt,constant dark and constant light showed that the expression of OsWRKY42 protein was significantly deceased under constant dark stress.Detached rice leaves were treated with different exogenous hormones and H2O2,OsWRKY42 protein expression decreased under MeJA,ABA and ET treatments,while increased slightly under H2O2 treatment.OsWRKY42-RNAi vector was transformed via agrobacterium-mediated method into 4021 plant,which harboring Xa21 gene.Transgenic plants with Xa21 background were obtained.Three OsWRKY42-RNAi homozygous transgenic lines were identified by PCR and WB.Statistical analysis of agronomic traits at maturity revealed that the plant height,tiller number,spike length and 1000-grain weight of transgenic plants were significantly lower than the control 4021.In addition,the contents of chlorophyll a,chlorophyll b and carotenoids in OsWRKY42-RNAi transgenic plants decreased significantly,and the ratio of chlorophyll a/b increased.These results indicated that the decrease of OsWRKY42 protein affected the normal growth and leaf development of rice.In the rice-Xoo interaction,the lesion length in OsWRKY42-RNAi transgenic plants increased significantly when compared with the control plant 4021,indicated that the Xa21-mediated resistance was impaired.The expression of pathogenesis-related proteins was survey in OsWRKY42-RNAi transgenic plants,it was found that the abundance of OsPR1A,OsPR1B,OsPR6,OsPR1A,OsPR15 and OsPR16 proteins were changed.However.the abundance of OsWRKY42 protein showed constant expression,independent of Xoo-inoculation.In addition,the seed germination rate of OsWRKY42-RNAi plants was lower than the control under salt stress,which suggested that the decrease of OsWRKY42 protein would reduce the salt tolerance.In summary,OsWRKY42 protein was expressed differently in different tissues of normal growth and development of rice.OsWRKY42 protein abundance changed under constant dark and different hormones,supporting that OsWRKY42 protein has multiple roles.The interference of OsWRKY42 protein in Xa21 background led to impaired bacterial blight resistance,which indicated that OsWRKY42 protein plays positive roles in Xa21mediated resistance response.This study enhances our understanding for the function of OsWRKY42 protein and the mechanism for Xa21-mediated resistance.