WRKY33-PIF4 Loop Is Required For Arabidopsis Growth And Development In Response To Abiotic Stress

Due to their sessile nature,higher plants are subjected to various adverse environmental conditions,including biotic and abiotic stresses.Plants have evolved sophisticated strategies to respond to these stresses known to induce reactive oxygen species?ROS?.One of the genes involved in this response is WRKY33,a transcription factor that can be induced by both biotic and abiotic stress.In this study,we generated transgenic Arabidopsis plants in the Ws ecotype?Ws?background in which WRKY33is co-suppressed?csWRKY33/Ws?.Compared with Ws,csWRKY33/Ws accumulates more H₂O₂.RNA-seq analysis indicated that in csWRKY33/Ws expression of genes such as PIF4 and STO is affected.Both PIF4 and WRKY33 are involved in red-light signalling and in abiotic stress responses,and we show that their expression is induced by NaCl and mannitol treatment.Further analysis revealed that PIF4 alters the expression of WRKY33 in response to biotic stress and vice versa.Seedlings of pif4 are more tolerant to NaCl,but more sensitive to mannitol while seedlings of csWRKY33/Ws are more sensitive to both NaCl and mannitol when grown on 1/2 MS medium.Moreover,expression of PIF4 and WRKY33 in response to salt and drought is affected in a reciprocal way when either of these factors is missing or its level decreased.Taken together,our results reveal a WRKY33-PIF4 regulatory loop that appears to play an important role in mediating abiotic stress responses and H₂O₂ homeostasis.