The rice Xa13 gene, whose promoter harbors a UPT (up-regulated by transcription activator-like [TAL] effector) box, UPTPthXo1, 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 UPTPthXo1 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 UPTPthXo1 boxes. In the Xa13 promoter, UPTPthXo1 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 UPTPthXo1 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.
水稻Xa13基因的啟動子含有一個UPT（up-regulated by transcription activator-like [TAL] effector）區(qū)域，UPTPthXo1。后者在由水稻白葉枯病菌PXO99菌株的種屬特異性致病力中發(fā)揮重要作用。PXO99通過誘導Xa13導致水稻患病。然而，對于在激活Xa13表達的過程中UPTPthXo1是否是唯一響應PXO99的順式作用元件仍然未知。我們分別切除Xa13啟動子區(qū)域的末端及中間部分并進行點突變，分析這三種情況下Xa13的表達，以及Xa13與完整的PXO99蛋白及其片段或者在UPT PthXo1盒點突變后的蛋白的結合情況。在響應水稻白葉枯病菌過程中，UPTPthXo1盒是在Xa13啟動子上唯一會引起PXO99誘導Xa13表達的順式作用因子。UPTPthXo1盒5’端的第二、第三、第四個核苷酸對于病菌蛋白的結合及基因的激活過程十分重要，這些位點中的任意一個突變都會導致PXO99誘導基因表達過程的徹底中斷。此外，UPTPthXo1盒的3’端的中間對于蛋白結合和基因激活過程也是必需的。這些結果將增強我們對于UPT和TAL因子介導的水稻和白葉枯病菌間相互作用的理解。
結果：對Xa13啟動子中病原響應區(qū)域的鑒定；與xa13的啟動子相比，更多的水稻白葉枯病蛋白結合到Xa13的啟動子片段上；UPTPthXo1盒的突變影響到PXO99誘導的轉錄活性。