植物自交不亲和基因研究进展

自交不亲和性的研究是植物生殖生物学和分子生物学研究的热点之一,对自交不亲和基因和蛋白质的深入研究是解析自交不亲和性机理的关键.对控制孢子体自交不亲和性和配子体自交不亲和性的S基因及其蛋白质产物的分子生物学研究进展进行了综述.孢子体自交不亲和性植物S位点上至少存在3个基因,即SLG、SRK和SCR基因.其中SLG、SRK基因控制雌蕊自交不亲和性,而SCR控制花粉自交不亲和性.配子体自交不亲和植物雌蕊S基因产物为S-RNase,具有核酸酶活性;配子体自交不亲和植物花粉S基因产物尚未找到.     

植物花粉S基因及其应用研究进展

自交不亲和性(self-incompatibility)研究是探讨植物遗传机制和植物育种的重要基础.在显花植物中,配子体自交不亲和由花柱S基因S-RNase和花粉S基因两个基因控制,这两个基因都具有较高的多态性和序列多样性的特征.花粉自交不亲和性是由花粉特异表达的F-box基因控制,命名为SFB(S haplotype-specific F-box protein)基因,并认为它就是花粉S基因的首选.就SFB基因的克隆、结构特点和作用机理以及应用予以综述.     

芸苔属植物自交不亲和性的分子机制

芸薹属植物自交不亲和性受单一位点的复等位基因控制,此位点命名为S位点。它决定柱头表面花粉识别的专一性。S位点糖蛋白基因（SLG）和S受体激酶基因（SRK）是控制芸薹属植物花柱自交不亲和性的两个关键因子。本文介绍了编码自交不亲和性的S位点的SLG、SRK和花粉S基因的鉴定、结构及功能,并对其信号传导途径的可能机制做了简要概述。     

芸薹属植物自交不亲和性的分子机制

芸薹属植物自交不亲和性受单一位点的复等位基因控制,此位点命名为S位点,它决定柱头表面花粉识别的专一性,S位点糖蛋白基因（SLG）和S受体激酶基因（SRK)是控制芸薹属植物花柱自交不亲和性的两个关键因子,本文介绍了编码自产不亲和性的S位点的SLG,SRK和花粉S基因的鉴定,结构及功能,并对其信号传导途径的可能机制做了简要概述。     

花粉特异F-box基因及其表达产物可能参与的SCF途径

泛素蛋白体目标性降解蛋白途径是许多细胞学过程的重要调节体系,底物蛋白泛素化涉及3个酶激反应,其中,作为E3连接酶的SCF复合体对底物的识别是通过亚体F-box蛋白C末端的特异性结构实现的.利用染色体步移等方法,最近在一些配子体型自交不亲和植物S-RNase基因近旁相继发现了一类花粉特异性表达的F-box基因,从而预示泛素介导的SCF蛋白降解途径可能参与配子体自交不亲和反应.     

植物的生殖讲座（五）：被子植物的自交不亲和性

自交不亲和性广泛存在于被子植物中,同形花与异型花均存在自交不亲和性。受精的障碍可发生在花粉萌发、花粉管进入柱头、花粉管在花柱中生长及进入胚囊中等不同阶段和部位。不亲和性由孢子体系统或配子体系统控制。用转基因技术研究发现甘蓝的ＳＬＧ启动子能控制配子体型和孢子体型的表达。配子体自交不亲和的Ｓ基因产物具有核酸酶的活性,能选择性地破坏不亲和花粉管的ＲＮＡ。本文简介了克服自交不亲和性的方法及自支不亲和性的利用。     

配子体自交不亲和植物花粉S基因研究进展

配子体自交不亲和植物的自交不亲和性是由雌蕊自交不亲和因子和花粉自交不亲和因子相互作用的结果。目前已经分离和鉴定了雌蕊自交不亲和基因及其表达产物。最近从金鱼草、Prumusdulcis、梅等植物中分离的F-box基因,它具有花粉S基因特点,即在花药、成熟的花粉和花粉管中特异表达;在基因位置上,与S-RNase基因紧密连锁;不同物种或同一物种不同品种F-box基因间核苷酸和氨基酸序列上存在高度多态性。通过分子生物学方法和杂交授粉试验证明所分离的F-box基因是花粉自交不亲和基因,但目前尚未分离出该类基因相应的表达蛋白。主要综述了配子体自交不亲和植物花粉自交不亲和基因的发现、基因的结构、雌蕊自交不亲和因子和花粉自交不亲和因子相互作用的模型。     

配子体自交不亲和信号转导的研究进展

自然界中大多数自交不亲和（self-incompatibility, SI）显花植物表现为配子体SI。配子体SI植物虽然都具有其SI的功能而阻止自我受精,但它们采取的信号转导途径是不同的。目前关于配子体SI信号转导的途径主要有两种：一是茄科、玄参科、蔷薇科中以雌蕊S-RNase为基础的信号转导途径;另一是罂粟科中以花粉管胞质自由钙离子为第二信使的转导途径。文章就配子体SI信号转导的研究进展作一综述。     

基于S- 核酸酶的自交不亲和性的分子机制

自交不亲和性是一种广泛存在于显花植物中的种内生殖障碍, 可以抑制近亲繁殖而促进异交。其中, 以茄科、玄参科和蔷薇科为代表的配子体自交不亲和性是最常见的类型。这类自交不亲和性是由单一的多态性S-位点所控制。目前的研究发现这一位点至少包含两个自交不亲和反应特异性决定因子: 花柱中的S-核酸酶和花粉中的SLF(S-Locus F-box)蛋白。该文将主要介绍并讨论基于S-核酸酶的自交不亲和性分子机制的研究进展。     

基于S-核酸酶的自交不亲和性的分子机制

自交不亲和性是一种广泛存在于显花植物中的种内生殖障碍,可以抑制近亲繁殖而促进异交。其中,以茄科、玄参科和蔷薇科为代表的配子体自交不亲和性是最常见的类型。这类自交不亲和性是由单一的多态性S-位点所控制。目前的研究发现这一位点至少包含两个自交不亲和反应特异性决定因子：花柱中的S-核酸酶和花粉中的SLF（S-Locus F-box）蛋白。该文将主要介绍并讨论基于S-核酸酶的自交不亲和性分子机制的研究进展。     

Plant self-incompatibility systems: a molecular evolutionary perspective

Incompatibility recognition systems preventing self-fertilization have evolved several times in independent lineages of Angiosperm plants, and three main model systems are well characterized at the molecular level [the gametophytic self-incompatibility (SI) systems of Solanaceae, Rosaceae and Anthirrhinum, the very different system of poppy, and the system in Brassicaceae with sporophytic control of pollen SI reactions]. In two of these systems, the genes encoding both components of pollen-pistil recognition are now known, showing clearly that these two proteins are distinct, that is, SI is a lock-and-key mechanism. Here, we review recent findings in the three well-studied systems in the light of these results and analyse their implications for understanding polymorphism and coevolution of the two SI genes, in the context of a tightly linked genome region.     

Membrane proteins involved in pollen-pistil interactions.

Self-incompatibility (SI) is a widespread mechanism in angiosperms which prevents self-fertilization. This mechanism relies on cell-cell interactions between pollen and pistil. Among the different SI systems that have been reported, two have been particularly investigated: the gametophytic system of Solanaceae and the sporophytic system of Brassicaceae. In these two families, although the molecular bases of SI response are different, secreted and/or membrane-anchored proteins are required for self-pollen rejection. Interestingly, these proteins exhibit two functions: recognition and a catalytic activity. In this review article, we present recent advances which permit a better understanding of how these proteins control the male/female recognition event associated with the SI response.     

How far are we from unravelling self-incompatibility in grasses?

The genetic and physiological mechanisms involved in limiting self-fertilization in angiosperms, referred to as self-incompatibility (SI), have significant effects on population structure and have potential diversification and evolutionary consequences. Up to now, details of the underlying genetic control and physiological basis of SI have been elucidated in two different gametophytic SI (GSI) systems, the S-RNase SI and the Papaver SI systems, and the sporophytic SI (SSI) system (Brassica). In the grass family (Poaceae), which contains all the cereal and major forage crops, SI has been known for half a century to be controlled gametophytically by two multiallelic and independent loci, S and Z. But still none of the gene products for S and Z is known and only limited information on related biochemical responses is available. Here we compare current knowledge of grass SI with that of other well-characterized SI systems and speculate about the relationship between SSI and grass SI. Additionally, we discuss comparative mapping as a tool for the further investigation of grass SI.     

Studies of self-incompatibility in wild tomatoes: I. S-allele diversity in Solanum chilense (Dun.) Reiche [corrected] (Solanaceae)

We characterized the molecular allelic variation of RNases at the self-incompatibility (SI) locus of Solanum chilense Dun. We recovered 30 S-RNase allele sequences from 34 plants representing a broad geographic sample. This yielded a species-wide estimate of 35 (95% likelihood interval 31-40) S-alleles. We performed crosses to confirm the association with SI function of 10 of the putative S-RNase allele sequences. Results in all cases were consistent with the expectation that these sequences represent functional alleles under single-locus gametophytic SI. We used the allele sequences to conduct an analysis of selection, as measured by the excess of nonsynonymous changes per site, and found evidence for adaptive changes both within the traditionally defined hypervariable regions and downstream, near the 3'-end of the molecule.     

Basi molecolari dell'interazione polline-stilo

Abstract

Molecular basis of pollen-style interaction - Pollen interaction with sporophytic “female” tissues leads to a block on tube growth within the style in the Angiosperm families under gametophytic control of self-incompatibility (SI). Primary events of the interaction may be described in terms of a signal-receptor model. Alternatively, a cytotoxic enzyme activity (RNase), located in the transmitting tract of the style, should be responsible for inhibition of the incompatible tubes, through degradation of pollen RNA and interference with protein synthesis. In several systems, the expression of the SI-controlling gene has been clarified on the female side (S-glycoproteins); by contrast, no conclusive evidence has been provided for the nature of the S-products in the male gametophyte.     

Selection of sporophytic and gametophytic self‐incompatibility in the absence of a superlocus

Self‐incompatibility (SI) is a complex trait that enforces outcrossing in plant populations. SI generally involves tight linkage of genes coding for the proteins that underlie self‐pollen detection and pollen identity specification. Here, we develop two‐locus genetic models to address the question of whether sporophytic SI (SSI) and gametophytic SI (GSI) can invade populations of self‐compatible plants when there is no linkage or weak linkage of the underlying pollen detection and identity genes (i.e., no S‐locus supergene). The models assume that SI evolves as a result of exaptation of genes formerly involved in functions other than SI. Model analysis reveals that SSI and GSI can invade populations even when the underlying genes are loosely linked, provided that inbreeding depression and selfing rate are sufficiently high. Reducing recombination between these genes makes conditions for invasion more lenient. These results can help account for multiple, independent evolution of SI systems as seems to have occurred in the angiosperms.     

Evolutionary Dynamics of Sporophytic Self-Incompatibility Alleles in Plants

The stationary frequency distribution and allelic dynamics in finite populations are analyzed through stochastic simulations in three models of single-locus, multi-allelic sporophytic self-incompatibility. The models differ in the dominance relationships among alleles. In one model, alleles act codominantly in both pollen and style (SSIcod), in the second, alleles form a dominance hierarchy in pollen and style (SSIdom). In the third model, alleles interact codominantly in the style and form a dominance hierarchy in the pollen (SSIdomcod). The SSIcod model behaves similarly to the model of gametophytic self-incompatibility, but the selection intensity is stronger. With dominance, dominant alleles invade the population more easily than recessive alleles and have a lower frequency at equilibrium. In the SSIdom model, recessive alleles have both a higher allele frequency and higher expected life span. In the SSIdomcod model, however, loss due to drift occurs more easily for pollen-recessive than for pollen-dominant alleles, and therefore, dominant alleles have a higher expected life span than the more recessive alleles. The process of allelic turnover in the SSIdomcod and SSIdom models is closely approximated by a random walk on a dominance ladder. Implications of the results for experimental studies of sporophytic self-incompatibility in natural populations are discussed.     

The different mechanisms of sporophytic self-incompatibility

Flowering plants have evolved a multitude of mechanisms to avoid self-fertilization and promote outbreeding. Self-incompatibility (SI) is by far the most common of these, and is found in ca. 60% of flowering plants. SI is a genetically controlled pollen-pistil recognition system that provides a barrier to fertilization by self and self-related pollen in hermaphrodite (usually co-sexual) flowering plants. Two genetically distinct forms of SI can be recognized: gametophytic SI (GSI) and sporophytic SI (SSI), distinguished by how the incompatibility phenotype of the pollen is determined. GSI appears to be the most common mode of SI and can operate through at least three different mechanisms, two of which have been characterized extensively at a molecular level in the Solanaceae and Papaveraceae. Because molecular studies of SSI have been largely confined to species from the Brassicaceae, predominantly Brassica species, it is not yet known whether SSI, like GSI, can operate through different molecular mechanisms. Molecular studies of SSI are now being carried out on Ipomoea trifida (Convolvulaceae) and Senecio squalidus (Asteraceae) and are providing important preliminary data suggesting that SSI in these two families does not share the same molecular mechanism as that of the Brassicaceae. Here, what is currently known about the molecular regulation of SSI in the Brassicaceae is briefly reviewed, and the emerging data on SSI in I. trifida, and more especially in S. squalidus, are discussed.     

Do homomorphic and heteromorphic self-incompatibility systems have the same sporophytic mechanism?

The view put forward by some authors that flowering plant self-incompatibility mechanisms of the homomorphic sporophytic and heteromorphic sporophytic types have a close evolutionary relationship, with one form being evolved from the other, or both forms directly evolved from ancestors with homomorphic gametophytic incompatibility, is challenged. A review is provided of the various facets of each of the three main self-incompatibility systems, including a detailed summary of our current knowledge of the rejection mechanism, to demonstrate that the implicit assumption that these systems have a common S locus, and also evolutionary theories linking the systems, need to be treated with considerable caution.     

Heat-shock proteins during pollen development in maize

In contrast to sporophytic tissues, mature pollen of higher plants does not synthesize the typical set of heat-shock proteins (HSPs) in response to a marked temperature upshift. Immature grains, however, seem able to do so, at least partially. We investigated the characteristics of HSP synthesis throughout the male gametophytic phase in maize and compared gametophytic and sporophytic heat-shock responses. One-dimensional Sodium dodecyl sulfate-polyacryl-amide gel electrophoresis technique (SDS-PAGE) of newly synthesized proteins revealed that immature pollen synthesizes HSPs, some of which are not induced in sporophytic tissues. The heat-shock response appeared to be related to microgametophytic developmental stages. The strongest response was found in uninucleate microspores: at this stage, in addition to the sporophytic 102, 84, 72, and 18 kD HSPs, three other polypeptides of 74, 56, and 46 kD were observed. In the binucleate and trinucleate stages, only a reduced synthesis of few HSPs could be induced, and differences between genotypes were observed. In germinating pollen, HSP synthesis was not induced under a voriety of heat-stress conditions; however, the consti-tutive synthesis of two polypeptides of the same molecular weight, 72 and 64 kD, as two HSPs was observed. The biological significance of these results is discussed.