The rice Xa13 gene, whose promoter harbors a UPT （up-regulated by transcription activator-like [TAL] effector） box, UPTpthXol, plays a pivotal role in the race-specific pathogenicity caused by Xanthomonas oryzae pv. oryzae （Xoo） strain PXO99. PxO99 causes rice disease by inducing Xa13. It is unknown, however, whether the UPTpthXol box is the only PXO99-responsive cis-regulating elements in the activation of Xa13 expression. We analyzed the expression of a series of end- and site-truncated and site-mutated Xa13 promoters in rice and the binding of PXO99 protein to the intact, partial, or site-mutated UPTpthxol boxes. In the Xa13 promoter, UPTpthxol box is the only Xoo-responsive cis-acting element that results in PXO99-induced Xa13 expression. The 5′-terminal second, third, and fourth nucleotides of the box are important for bacterial protein binding and gene activation; mutation of any one of these sites abolished PXO99-induced gene expression. Furthermore, the 3′-half of the UPTpthXol box is also required for protein binding and gene activation. These findings will enhance our understanding of the molecular mechanism of the interaction of rice and Xoo via UPT boxes and TAL effectors.
Despite the importance of quantitative disease resistance during a plant’s life, little is known about the molecular basis of this type of host-pathogen interaction, because most of the genes underlying resistance quantitative trait loci (QTLs) are unknown. To identify genes contributing to resistance QTLs in rice, we analyzed the colocalization of a set of characterized rice defense-responsive genes and resistance QTLs against different pathogens. We also examined the expression patterns of these genes in response to pathogen infection in the parents of the mapping populations, based on the strategy of validation and functional analysis of the QTLs. The results suggest that defense-responsive genes are important resources of resistance QTLs in rice. OsWRKY45-1 is the gene contributing to a major resistance QTL.NRR,OsGH3-1,and OsGLP members on chromosome 8 contribute alone or collectively to different minor resistance QTLs. These genes function in a basal resistance pathway or in major disease resistance gene-mediated race-specific pathways.
KOU YanJun, LI XiangHua, XIAO JingHua & WANG ShiPing National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research (Wuhan),Huazhong Agricultural University, Wuhan 430070, China
