Cohn Megan, Morbitzer Robert, Lahaye Thomas, Staskawicz Brian J
Department of Plant and Microbial Biology, University of California, Berkeley, CA, 94720-3120, USA.
Department of General Genetics, Center of Plant Molecular Biology (ZMBP) University of Tübingen, D-72076, Tübingen, Germany.
Mol Plant Pathol. 2016 Aug;17(6):875-89. doi: 10.1111/mpp.12337. Epub 2016 Feb 8.
Xanthomonas axonopodis pv. manihotis (Xam) employs transcription activator-like (TAL) effectors to promote bacterial growth and symptom formation during infection of cassava. TAL effectors are secreted via the bacterial type III secretion system into plant cells, where they are directed to the nucleus, bind DNA in plant promoters and activate the expression of downstream genes. The DNA-binding activity of TAL effectors is carried out by a central domain which contains a series of repeat variable diresidues (RVDs) that dictate the sequence of bound nucleotides. TAL14Xam668 promotes virulence in Xam strain Xam668 and has been shown to activate multiple cassava genes. In this study, we used RNA sequencing to identify the full target repertoire of TAL14Xam668 in cassava, which includes over 50 genes. A subset of highly up-regulated genes was tested for activation by TAL14CIO151 from Xam strain CIO151. Although TAL14CIO151 and TAL14Xam668 differ by only a single RVD, they display differential activation of gene targets. TAL14CIO151 complements the TAL14Xam668 mutant defect, implying that shared target genes are important for TAL14Xam668 -mediated disease susceptibility. Complementation with closely related TAL effectors is a novel approach to the narrowing down of biologically relevant susceptibility genes of TAL effectors with multiple targets. This study provides an example of how TAL effector target activation by two strains within a single species of Xanthomonas can be dramatically affected by a small change in RVD-nucleotide affinity at a single site, and reflects the parameters of RVD-nucleotide interaction determined using designer TAL effectors in transient systems.
木薯细菌性枯萎病菌（Xanthomonas axonopodis pv. manihotis，Xam）在侵染木薯过程中利用转录激活样（TAL）效应子来促进细菌生长和症状形成。TAL效应子通过细菌III型分泌系统分泌到植物细胞中，然后被转运至细胞核，结合植物启动子中的DNA并激活下游基因的表达。TAL效应子的DNA结合活性由一个中央结构域执行，该结构域包含一系列重复可变双残基（RVD），这些RVD决定了所结合核苷酸的序列。TAL14Xam668可促进Xam菌株Xam668的致病性，并且已证明它能激活多个木薯基因。在本研究中，我们利用RNA测序来鉴定木薯中TAL14Xam668的完整靶标库，其中包括50多个基因。对一组高度上调的基因进行了测试，以检测来自Xam菌株CIO151的TAL14CIO151对其的激活作用。尽管TAL14CIO151和TAL14Xam668仅相差一个RVD，但它们对基因靶标的激活表现出差异。TAL14CIO151可弥补TAL14Xam668突变体的缺陷，这意味着共享的靶标基因对TAL14Xam668介导的感病性很重要。用密切相关的TAL效应子进行互补是一种缩小具有多个靶标的TAL效应子生物学相关感病基因范围的新方法。本研究提供了一个实例，说明在单个黄单胞菌物种内，两个菌株对TAL效应子靶标的激活如何会因单个位点RVD-核苷酸亲和力的微小变化而受到显著影响，并且反映了在瞬时系统中使用设计的TAL效应子所确定的RVD-核苷酸相互作用参数。
