PROTEIN CHEMISTRY ON SELF-POLLEN RECOGNITION SYSTEM IN PLANT

1.花粉配基SP11的溶液结构许多开花植物都具有防止近亲交配的自交不亲和系统。在甘蓝属植物中，交配过程中的自我/非自我识别是通过柱头受体激酶SPK与其花粉配基SP11之间的S单倍型特异性相互作用来建立的。在本研究中，我们用核磁共振波谱测定了S_8-单倍型(S_8-SP11)SP11蛋白的溶液结构。它可以折叠成α/β三明治结构，类似于植物防御素。对结构完整性重要的残基在等位基因SP11s中高度保守，表明存在共同的折叠模式。基于结构的序列比对和等位基因SP11的同源建模确定了一个高变量(HV)区域，该区域被认为形成了一个从蛋白质体内凸出的环，该环容易受到溶剂的影响。我们认为HV区可以作为柱头受体的特异性结合部位。2.发现MLPK，这是柱头受体复合体的一个可能成分。油菜的SI反应是由花粉-骨配体SP11和其柱头受体激酶SRK之间的单倍型特异性相互作用启动的。这种结合诱导了SRK的自磷酸化，然后被认为触发了导致自交排斥的信号级联反应。修饰(M)基因的隐性突变消除了柱头的SI反应。M的定位克隆表明，它编码一种膜锚定的细胞质丝氨酸/苏氨酸蛋白激酶，称为MLPK。MLPK的瞬时表达恢复了mm乳头细胞拒绝自交花粉的能力，这表明MLPK是油菜SI信号的一个积极的中介。MLPK的质膜定位表明它可能在SRK附近发挥作用。MLPK作用于SRK受体复合体，是未来SI信号研究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.