INRA, UMR Interactions Biotiques et Santé Végétale INRA 1301, CNRS, UMR CNRS 6243, and Université de Nice Sophia-Antipolis, F-06903 Sophia-Antipolis, France.
Plant Physiol. 2011 Jun;156(2):779-92. doi: 10.1104/pp.111.176230. Epub 2011 Apr 11.
Root-knot nematode (RKN) Meloidogyne species are major polyphagous pests of most crops worldwide, and cultivars with durable resistance are urgently needed because of nematicide bans. The Ma gene from the Myrobalan plum (Prunus cerasifera) confers complete-spectrum, heat-stable, and high-level resistance to RKN, which is remarkable in comparison with the Mi-1 gene from tomato (Solanum lycopersicum), the sole RKN resistance gene cloned. We report here the positional cloning and the functional validation of the Ma locus present at the heterozygous state in the P.2175 accession. High-resolution mapping totaling over 3,000 segregants reduced the Ma locus interval to a 32-kb cluster of three Toll/Interleukin1 Receptor-Nucleotide Binding Site-Leucine-Rich Repeat (LRR) genes (TNL1-TNL3), including a pseudogene (TNL2) and a truncated gene (TNL3). The sole complete gene in this interval (TNL1) was validated as Ma, as it conferred the same complete-spectrum and high-level resistance (as in P.2175) using its genomic sequence and native promoter region in Agrobacterium rhizogenes-transformed hairy roots and composite plants. The full-length cDNA (2,048 amino acids) of Ma is the longest of all Resistance genes cloned to date. Its TNL structure is completed by a huge post-LRR (PL) sequence (1,088 amino acids) comprising five repeated carboxyl-terminal PL exons with two conserved motifs. The amino-terminal region (213 amino acids) of the LRR exon is conserved between alleles and contrasts with the high interallelic polymorphisms of its distal region (111 amino acids) and of PL domains. The Ma gene highlights the importance of these uncharacterized PL domains, which may be involved in pathogen recognition through the decoy hypothesis or in nuclear signaling.
根结线虫（RKN）是世界上大多数作物的主要多食性害虫，由于杀线虫剂的禁用，迫切需要具有持久抗性的品种。李属扁桃（Prunus cerasifera）的 Ma 基因赋予了广谱、耐热和高水平的 RKN 抗性，与唯一克隆的番茄（Solanum lycopersicum）Mi-1 基因相比，这是显著的。我们在这里报道了 P.2175 品系中杂合状态下的 Ma 基因座的定位克隆和功能验证。超过 3000 个分离物的高分辨率图谱将 Ma 基因座区间缩小到一个由三个 Toll/白细胞介素 1 受体-核苷酸结合位点-亮氨酸-富含重复序列（LRR）基因（TNL1-TNL3）组成的 32-kb 簇，包括一个假基因（TNL2）和一个截断基因（TNL3）。该区间内唯一完整的基因（TNL1）被验证为 Ma，因为它使用其基因组序列和根癌农杆菌转化的毛状根和复合植物中的天然启动子区域，赋予了相同的广谱和高水平抗性（如在 P.2175 中）。Ma 的全长 cDNA（2048 个氨基酸）是迄今为止克隆的所有抗性基因中最长的。其 TNL 结构由一个巨大的 LRR 后区（PL）序列（1088 个氨基酸）完成，该序列包含五个重复的羧基末端 PL 外显子，其中有两个保守基序。LRR 外显子的氨基末端区域（213 个氨基酸）在等位基因之间是保守的，而其远端区域（111 个氨基酸）和 PL 结构域的等位基因间多态性很高。Ma 基因强调了这些未表征的 PL 结构域的重要性，它们可能通过诱饵假说参与病原体识别或核信号转导。
