Huguet E, Bonas U
Institut des Sciences Végétales, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Mol Plant Microbe Interact. 1997 May;10(4):488-98. doi: 10.1094/MPMI.1997.10.4.488.
The gram-negative bacterium Xanthomonas campestris pv. vesicatoria is the causal agent of bacterial spot disease on pepper and tomato plants. The main hrp (hypersensitive reaction and pathogenicity) gene cluster in X. campestris pv. vesicatoria spans a 23-kb chromosomal region, comprising six complementation groups designated hrpA to hrpF. Analysis of the hrpF locus revealed a single open reading frame encoding HrpF (86.4 kDa). HrpF is predominantly hydrophilic, and contains two hydrophobic domains in the C terminus. An interesting feature is the presence of two imperfect direct repeats in the N-terminal region. Deletion studies showed that one repeat is sufficient for function. Epitope tagging of HrpF allowed detection of the protein in X. campestris pv. vesicatoria. Subcellular localization studies suggest that HrpF is both in the soluble fraction and in the inner membrane. Interestingly, HrpF is 48% identical (67% similar) to the Rhizobium fredii NoIX protein that is part of the host specificity locus. Since several Hrp proteins are believed to be components of the types of III hrp protein secretion apparatus, allowing export of proteins essential for the interaction with the plant, the possible role of hrpF and NoIX in secretion is discussed.
革兰氏阴性菌野油菜黄单胞菌辣椒斑点病致病变种是辣椒和番茄植株细菌性斑点病的病原体。野油菜黄单胞菌辣椒斑点病致病变种中的主要hrp（过敏反应和致病性）基因簇跨越一个23 kb的染色体区域，由六个互补群组成，分别命名为hrpA至hrpF。对hrpF基因座的分析揭示了一个编码HrpF（86.4 kDa）的单一开放阅读框。HrpF主要是亲水性的，在C末端含有两个疏水域。一个有趣的特征是在N末端区域存在两个不完全的直接重复序列。缺失研究表明，一个重复序列就足以发挥功能。对HrpF进行表位标记可检测到野油菜黄单胞菌辣椒斑点病致病变种中的该蛋白。亚细胞定位研究表明，HrpF既存在于可溶性部分，也存在于内膜中。有趣的是，HrpF与作为宿主特异性基因座一部分的费氏中华根瘤菌NoIX蛋白有48%的同一性（67%的相似性）。由于几种Hrp蛋白被认为是III型hrp蛋白分泌装置的组成部分，可使与植物相互作用所必需的蛋白质得以输出，因此讨论了hrpF和NoIX在分泌中的可能作用。
