GENE-FOR-GENES INTERACTIONS BETWEEN COTTON R-GENES AND XANTHOMONAS-CAMPESTRIS PV MALVACEARUM AVR GENES
GENE-FOR-GENES INTERACTIONS BETWEEN COTTON R-GENES AND XANTHOMONAS-CAMPESTRIS PV MALVACEARUM AVR GENES
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DOI：
10.1094/mpmi-6-225
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发表时间：
1993-03-01
影响因子：
3.5
通讯作者：
GABRIEL, DW
中科院分区：
文献类型：
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作者：
DEFEYTER, R;YANG, YO;GABRIEL, DW
先前从棉花病原菌野油菜黄单胞菌锦葵致病变种（Xanthomonas campestris pv. malvacearum）的XcmH菌株中克隆出了6个质粒携带的无毒力（avr）基因。我们现在通过亚克隆和Tn5 - gusA插入诱变将所有6个avr基因定位在克隆片段上。这些avr基因似乎都没有表现出与棉花R基因完全的基因对基因相互作用模式，并且已证明avrB4能使野油菜黄单胞菌锦葵致病变种对携带两个不同抗性位点B1或B4中任意一个的同源棉花品系表现出avr基因对多个R基因的无毒力。此外，B1位点似乎能使棉花对携带avrB4、avrb6或avrB102这三个avr基因中任意一个的同基因野油菜黄单胞菌锦葵致病变种菌株表现出R基因对多个avr基因的抗性。限制酶分析、Southern杂交和DNA序列分析表明，XcmH的avr基因彼此之间高度相似，与辣椒病原菌野油菜黄单胞菌辣椒斑点致病变种（X. c. pv. vesicatoria）的avrBs3和avrBsP以及柑橘病原菌柑橘黄单胞菌（X. citri）的寄主特异性毒力基因pthA也高度相似。XcmH的avr基因主要在基因中部串联重复的102个碱基对基序的重复次数上有所不同，在这个基因家族的成员中重复14到23次。avrb6的完整核苷酸序列显示，它在DNA序列上与avrB4、avrBs3、avrBsP和pthA有97%的同一性，并且62个碱基对的反向末端重复标记了avrb6与迄今为止已测序的这个黄单胞菌毒力/无毒力基因家族所有成员之间的同源边界。两个反向重复的末端38个碱基对与Tn3转座子家族的38个碱基对的共有末端序列高度相似。在野油菜黄单胞菌锦葵致病变种的北美菌株（包括XcmH）中似乎存在多达11个avr基因家族成员。在这些avr基因中观察到的高度同源性以及它们的多拷贝存在可能解释了基因对基因的相互作用，也解释了观察到的野油菜黄单胞菌生理小种变化突变的高频率（每个位点10⁻³到10⁻⁴）。XcmH的5个自发生理小种变化突变体发生了avr位点缺失，这有力地表明基因间重组是野油菜黄单胞菌锦葵致病变种产生新生理小种的主要机制。
Six plasmid-borne avirulence (avr) genes were previously cloned from strain XcmH of the cotton pathogen, Xanthomonas campestris pv. malvacearum. We have now localized all six avr genes on the cloned fragments by subcloning and Tn5-gusA insertional mutagenesis. None of these avr genes appeared to exhibit exclusively gene-for-gene patterns of interactions with cotton R genes, and avrB4 was demonstrated to confer avr gene-for-R genes (plural) avirulence to X. c. pv. malvacearum on congenic cotton lines carrying either of two different resistance loci, B1 or B4. Furthermore, the B1 locus appeared to confer R gene-for-avr genes resistance to cotton against isogenic X. c. pv. malvacearum strains carrying any one of three avr genes: avrB4, avrb6, or avrB102. Restriction enzyme, Southern blot hybridization, and DNA sequence analyses showed that the XcmH avr genes are all highly similar to each other, to avrBs3 and avrBsP from the pepper pathogen X. c. pv. vesicatoria, and to the host-specific virulence gene pthA from the citrus pathogen X. citri. The XcmH avr genes differed primarily in the multiplicity of a tandemly repeated 102-base pair motif within the central portions of the genes, repeated from 14 to 23 times in members of this gene family. The complete nucleotide sequence of avrb6 revealed that it is 97% identical in DNA sequence to avrB4, avrBs3, avrBsP, and pthA and that 62-bp inverted terminal repeats mark the boundaries of homology between avrb6 and all members of this Xanthomonas virulence/avirulence gene family sequenced to date. The terminal 38 bp of both inverted repeats are highly similar to the 38-bp consensus terminal sequence of the Tn3 family of transposons. Up to 11 members of the avr gene family appear to be present in North American strains of X. c. pv. malvacearum, including XcmH. The high level of homology observed among these avr genes and their presence in multiple copies may explain the gene-for-genes interactions and also the observed high frequencies (10(-3) to 10(-4) per locus) of X. c. pv. malvacearum race change mutations. Five spontaneous race change mutants of XcmH suffered avr locus deletions, strongly indicating intergenic recombination as the primary mechanism for generating new races in X. c. pv. malvacearum.