Abstract
Plants use a complex signal transduction network to regulate their adaptation to the ever-changing environment. Rice (Oryza sativa) WRKY13 plays a vital role in the cross talk between abiotic and biotic stress signaling pathways by suppressing abiotic stress resistance and activating disease resistance. However, it is not clear how WRKY13 directly regulates this cross talk. Here, we show that WRKY13 is a transcriptional repressor. During the rice responses to drought stress and bacterial infection, WRKY13 selectively bound to certain site- and sequence-specific cis-elements on the promoters of SNAC1 (for STRESS RESPONSIVE NO APICAL MERISTEM, ARABIDOPSIS TRANSCRIPTION ACTIVATION FACTOR1/2, CUP-SHAPED COTYLEDON), the overexpression of which increases drought resistance, and WRKY45-1, the knockout of which increases both bacterial disease and drought resistance. WRKY13 also bound to two cis-elements of its native promoter to autoregulate the balance of its gene expression in different physiological activities. WRKY13 was induced in leaf vascular tissue, where bacteria proliferate, during infection, and in guard cells, where the transcriptional factor SNAC1 enhances drought resistance, during both bacterial infection and drought stress. These results suggest that WRKY13 regulates the antagonistic cross talk between drought and disease resistance pathways by directly suppressing SNAC1 and WRKY45-1 and autoregulating its own expression via site- and sequence-specific cis-elements on the promoters of these genes in vascular tissue where bacteria proliferate and guard cells where the transcriptional factor SNAC1 mediates drought resistance by promoting stomatal closure.
Highlights
Plants use a complex signal transduction network to regulate their adaptation to the ever-changing environment
The GFP transcript level in the wildtype calli was significantly higher (P, 0.05) than that in WRKY13-oe calli. These results suggest that WRKY13 is a transcriptional repressor that suppresses SNAC1 and WRKY45-1 but perhaps it own gene as well
WBOX1 and WBOX3 are the same type of cis-elements but with different flanking sequences (Supplemental Fig. S2), indicating the binding specificity of WRKY13 to the DNA segment harboring WBOX1. These results suggest that WRKY13 binds to the promoter of SNAC1 in vivo; it may preferentially bind to the WBOX1 cis-element of the SNAC1 promoter both with and without abiotic and biotic stresses
Summary
Plants use a complex signal transduction network to regulate their adaptation to the ever-changing environment. WRKY13 can bind to its own gene promoter via a W-like box and a non-W or non-W-like box cis-element in vitro (Qiu et al, 2007; Cai et al, 2008) It remains to be determined whether WRKY13 is a transcriptional repressor and whether it directly regulates SNAC1 and its own gene expression in rice. It is unclear which ciselements on the promoter of WRKY45 are essential for WRKY13 binding during rice responses to abiotic and biotic stresses
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