Regulation of rice responses to submergence by WRKY transcription factors

Responses of rice to submergence have been extensively studied, but the molecular network behind the tolerance to this stress is still incomplete. Transcription factors (TFs) are important players in gene transcription regulation during stresses. Here, we analyzed expression of WRKY genes and morphological and anatomical changes in different rice cultivars under submergence. When they were submerged for 48 h, changes in root number, fresh and dry masses, and aerenchyma development were observed. Although accumulations of WRKY transcripts were observed in both shoots and roots, root tissues showed higher accumulation with a peak already after 6 h under submergence. Especially transcriptions of OsWRKY11 and OsWRKY56 were high, more than 100-fold in comparison with controls. The WRKY promoter analysis showed that some cis-regulatory elements could be characterized as stress-responsive elements and linked to oxygen depletion. In the promoter of OsWRKY62, two cis-regulatory elements were found: ARE and GC-motif. These elements are known to be involved in oxygen deficiency responses. In addition, the W-box cis-regulatory element, the target of WRKY transcription factors, was found in OsWRKY11, OsWRKY56, and OsWRKY62, suggesting a feedback control acting on the upregulation of WRKY transcription factors. Genes involved in the submergence stress and resulting aerenchyma development had a W-box in their promoter regions, which also suggested regulation by WRKYs. Overall, the results support the role of WRKY transcription factors in rice submergence tolerance and unveil their action in other tolerance mechanisms.