PROTEIN CHEMISTRY ON SELF-POLLEN RECOGNITION SYSTEM IN PLANT

1.花粉配体SP11的溶液结构许多有花植物具有防止近亲繁殖的自交不亲和（SI）系统。在芸苔属中，交配中的自我/非自我识别是通过柱头受体激酶SPK及其花粉配体SP11之间的S-单倍型特异性相互作用建立的。本研究利用核磁共振波谱技术测定了S_8单倍型（S_8-SP11）的SP11蛋白的溶液结构。它折叠成类似于植物防御素的α/β三明治结构。对结构完整性重要的残基在等位基因SP11之间高度保守，表明存在共同的折叠模式。等位基因SP11的基于结构的序列比对和同源性建模确定了一个高变（HV）区域，该区域被认为形成了一个环，该环从易于溶剂暴露的蛋白质体凸出。我们认为HV区可能是柱头受体的特异性结合位点。2. MLPK的发现，MLPK可能是柱头受体复合物的一个组成部分。这种结合诱导SRK的自磷酸化，然后认为其触发导致自花粉排斥的信号级联。修饰基因（m）的隐性突变消除了柱头的SI反应。定位克隆的M已经揭示，它编码膜锚定的细胞质丝氨酸/苏氨酸蛋白激酶，指定MLPK。MLPK的瞬时表达恢复了mm乳突细胞拒绝自花花粉的能力，表明MLPK是芸苔属SI信号传导的正介体。MLPK的质膜定位表明它可能在SRK附近发挥作用。MLPK在SRK受体复合物中起作用，是未来研究SI信号传导的一个有吸引力的模型。

1.Solution structure of the pollen ligand, SP11Many flowering plants possess a self-incompatibility (SI) system to prevent inbreeding. In Brassica, self/non-self recognition in mating is established through S-haplotype specific interactions between stigmatic receptor kinase, SPK, and its pollen ligand, SP11. In this study, we determined the solution structure of the SP11 protein of the S_8-haplotype (S_8-SP11) by using NMR spectroscopy. It folds into an α/β sandwich structure that resembles those of plant defensins. Residues important for structural integrity are highly conserved among the allelic SP11s, suggesting the existence of a common folding pattern. Structure-based sequence alignment and homology modeling of allelic SP11s identified a hypervariable (HV) region, which is thought to form a loop that bulges out from the body of the protein that is amenable to solvent exposure. We suggest that the HV region could serve as a specific binding site for the stigma receptor.2.Finding of MLPK, a possible component of the stigmatic receptor complex.SI response in Brassica is initiated by haplotype-specific interactions between the pollen-bome ligand SP11 and its stigmatic receptor kinase SRK. This binding induces autophosphorylation of SRK, which is then thought to trigger a signaling cascade that leads to self-pollen rejection. A recessive mutation of the modifier (m) gene eliminates the SI response in stigma. Positional cloning of M has revealed that it encodes a membrane-anchored cytoplasmic serine/threonine protein kinase, designated MLPK. Transient expression of MLPK restores the ability of mm papilla cells to reject self-pollen, suggesting that MLPK is a positive mediator of Brassica SI signaling. The plasma membrane localization of MLPK suggests that it may function in the vicinity of SRK. MLPK, acting within the SRK receptor complex, is an attractive model for the future study of SI signaling.