Farina Anna, Rocchi Valentina, Janni Michela, Benedettelli Stefano, De Lorenzo Giulia, D'Ovidio Renato
Dipartimento di Agrobiologia e Agrochimica, Università della Tuscia, Viterbo, Italy.
Theor Appl Genet. 2009 May;118(7):1371-9. doi: 10.1007/s00122-009-0987-4. Epub 2009 Feb 24.
Polygalacturonase-inhibiting proteins (PGIPs) are extracellular plant protein inhibitors of endo-polygalacturonases (PGs) that belong to the leucine-rich repeat (LRR) protein family. In bean, PGIP is encoded by a small gene family of four members among which Pvpgip2 encodes the most wide-spectrum and efficient inhibitor of fungal PGs. In order to evaluate the sequence polymorphism of Pvpgip2 and its functional significance, we have analyzed a number of wild and cultivated bean (P. vulgaris) accessions of Andean and Mesoamerican origin, and some genotypes from the related species P. coccineus, P. acutifolius, and P. lunatus. Our analyses indicate that the protein encoded by Pvpgip2 is highly conserved in the bean germplasm. The few detected polymorphic sites correspond to synonymous substitutions and only two wild genotypes contain a Pvpgip2 with a single non-synonymous replacement. Sequence comparison showed a slightly larger variation in the related bean species P. coccineus, P. acutifolius, and P. lunatus and confirmed the known phylogenetic relationships with P. vulgaris. The majority of the replacements were within the xxLxLxx region of the leucine rich repeat (LRR) domain and none of them affected residues contributing to structural features. The variant PGIPs were expressed in Nicotiana benthamiana using PVX as vector and their inhibitory activity compared to that of PvPPGIP2. All the variants were able to fully inhibit the four fungal PGs tested with minor differences. Taken together these results support the hypothesis that the overall sequence conservation of PGIP2 and minor variation at specific sites is necessary for high-affinity recognition of different fungal PGs.
多聚半乳糖醛酸酶抑制蛋白（PGIPs）是植物细胞外的内切多聚半乳糖醛酸酶（PGs）抑制蛋白，属于富含亮氨酸重复序列（LRR）蛋白家族。在菜豆中，PGIP由一个包含四个成员的小基因家族编码，其中Pvpgip2编码的真菌PGs抑制剂具有最广的光谱范围和最高的效率。为了评估Pvpgip2的序列多态性及其功能意义，我们分析了许多源自安第斯和中美洲的野生和栽培菜豆（P. vulgaris）种质，以及一些来自相关物种多花菜豆（P. coccineus）、尖叶菜豆（P. acutifolius）和利马豆（P. lunatus）的基因型。我们的分析表明，Pvpgip2编码的蛋白在菜豆种质中高度保守。检测到的少数多态性位点对应于同义替换，只有两个野生基因型含有一个具有单个非同义替换的Pvpgip2。序列比较显示，在相关的菜豆物种多花菜豆、尖叶菜豆和利马豆中变异稍大，并证实了与菜豆已知的系统发育关系。大多数替换发生在富含亮氨酸重复序列（LRR）结构域的xxLxLxx区域内，且没有一个影响到构成结构特征的残基。使用PVX作为载体在本氏烟草中表达变异的PGIPs，并将它们的抑制活性与PvPPGIP2的抑制活性进行比较。所有变异体都能够完全抑制所测试的四种真菌PGs，只是存在微小差异。综合这些结果支持了这样一种假说，即PGIP2的整体序列保守性以及特定位点的微小变异对于高亲和力识别不同的真菌PGs是必要的。
