Department of Microbiology and Plant Pathology, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0002, South Africa.
Mol Plant Microbe Interact. 2012 Apr;25(4):546-56. doi: 10.1094/MPMI-06-11-0166.
Type IV pili are virulence factors in various bacteria. Several subclasses of type IV pili have been described according to the characteristics of the structural prepilin subunit. Although type IVa pili have been implicated in the virulence of Ralstonia solanacearum, type IVb pili have not previously been described in this plant pathogen. Here, we report the characterization of two distinct tad loci in the R. solanacearum genome. The tad genes encode functions necessary for biogenesis of the Flp subfamily of type IVb pili initially described for the periodontal pathogen Aggregatibacter actinomycetemcomitans. To determine the role of the tad loci in R. solanacearum virulence, we mutated the tadA2 gene located in the megaplasmid that encodes a predicted NTPase previously reported to function as the energizer for Flp pilus biogenesis. Characterization of the tadA2 mutant revealed that it was not growth impaired in vitro or in planta, produced wild-type levels of exopolysaccharide galactosamine, and exhibited swimming and twitching motility comparable with the wild-type strain. However, the tadA2 mutant was impaired in its ability to cause wilting of potato plants. This is the first report where type IVb pili in a phytopathogenic bacterium contribute significantly to plant pathogenesis.
IV 型菌毛是多种细菌的毒力因子。根据结构前菌毛亚基的特征，已经描述了几种类别的 IV 型菌毛。虽然 IVa 型菌毛与罗尔斯通氏菌的毒力有关，但以前在这种植物病原体中没有描述过 IVb 型菌毛。在这里，我们报告了罗尔斯通氏菌基因组中两个不同 tad 基因座的特征。tad 基因编码了最初在牙周病原体伴放线放线杆菌中描述的 Flp 亚家族 IVb 型菌毛生物发生所必需的功能。为了确定 tad 基因座在罗尔斯通氏菌毒力中的作用，我们突变了位于编码先前报道的作为 Flp 菌毛生物发生能量器的 NTPase 的大质粒中的 tadA2 基因。tadA2 突变体的特征表明，它在体外或体内生长不受影响，产生与野生型菌株相当的外多糖半乳糖胺水平，并且表现出与野生型菌株相当的泳动和蠕动运动。然而，tadA2 突变体在引起马铃薯植株萎蔫的能力上受到了损害。这是首次报道植物病原细菌中的 IVb 型菌毛对植物发病机制有重要贡献。
