基于RNA-seq技术对乌头属铁棒锤中自交不亲和S基因的挖掘与分析

以毛茛科乌头属铁棒锤(Aconitum pendulum N.Busch)2个品系‘蓝花铁棒锤’(‘WSYB1’)和‘黄花铁棒锤’(‘WSYY1’)为材料,对其进行转录组测序(RNA-seq),采用生物信息学方法鉴定其中可能存在的花柱S基因(self-incompatibility gene)和花粉S基因,并对它们的序列特征进行分析。结果显示,转录组中共鉴定出2个在雌蕊中特异或高表达的花柱S基因(ApSRNase)和2个在雄蕊中特异表达的花粉S基因(ApSLF)。与耧斗菜(Aquilegia coerulea James)相似,铁棒锤中也存在S-RNase(S locus ribonucleases)和SLF(S locus F-box)控制的S-RNase类的自交不亲和系统,而不存在sS(stigma S-determinant)和pS(pollen S-determinant)控制的罂粟科类型的自交不亲和系统。     

S-RNases and sexual incompatibility: structure, functions, and evolutionary perspectives

S-RNase-based gametophytic self-incompatibility appears to be the most phylogenetically widespread form of self-incompatibility found in the angiosperms, having been reported in the Solanaceae, Scrophulariaceae, and Rosaceae. This intraspecific breeding barrier is controlled by a single genetic locus termed S. Rejection of self-pollen has been shown to be mediated in the pistil by a highly polymorphic series of ribonucleases, but as yet the pollen component of this recognition system has not been identified. Here we review our present knowledge concerning the structure, functions, and evolution of S-RNases and the S-loci in which they reside. In addition we present two new phylogenetic analyses of S-RNases which suggest that (1). sequence variability between S-alleles is spread across the whole gene and is not as clustered as is generally believed and (2). there is evidence of recombination and/or diversifying selection in two distinct regions of S-RNases. The implications of these findings are discussed.     

Identification of Self-Incompatibility Genotypes of Apricot (<Emphasis Type="Italic">Prunus armeniaca</Emphasis> L.) by S-Allele-Specific PCR Analysis

A cDNA of 417 bp encoding an S-RNase gene, named PA S3, was isolated from apricot, Prunus aremeniaca. Nine S-alleles, S₁–S₉, were recognized by S-allele-specific PCR and confirmed by Southern blot analysis using PA S3 as probe. The S-genotypes of the six cultivars were determined and the results of self- and cross-pollination tests among the six cultivars were consistent with the predicted S-haplotypes by PCR analysis.     

Gametophytic self-incompatibility: understanding the cellular mechanisms involved in “self” pollen tube inhibition

Self-incompatibility (SI) prevents the production of “self” seed and inbreeding by providing a recognition and rejection system for “self,” or genetically identical, pollen. Studies of gametophytic SI (GSI) species at a molecular level have identified two completely different S-genes and SI mechanisms. One GSI mechanism, which is found in the Solanaceae, Rosaceae and Scrophulariaceae, has S-RNase as the pistil S-component and an F-box protein as the pollen S-component. However, non-S-locus factors are also required. In an incompatible situation, the S-RNases degrade pollen RNA, thereby preventing pollen tube growth. Here, in the light of recent evidence, we examine alternative models for how compatible pollen escapes this cytotoxic activity. The other GSI mechanism, so far found only in the Papaveraceae, has a small secreted peptide, the S-protein, as its pistil S-component. The pollen S-component remains elusive, but it is thought to be a transmembrane receptor, as interaction of the S-protein with incompatible pollen triggers a signaling network, resulting in rapid actin depolymerization and pollen tube inhibition and programmed cell death (PCD). Here, we present an overview of what is currently known about the mechanisms involved in regulating pollen tube inhibition in these two GSI systems.     

Early F-actin disorganization may be signaling vacuole disruption in incompatible pollen tubes of Nicotiana alata

Self-incompatibility (SI) systems appeared early in plant evolution as an effective mechanism to promote outcrossing and avoid inbreeding depression. These systems prevent self-fertilization by the recognition and rejection of self-pollen and pollen from closely related individuals. The most widespread SI system is based on the action of a pistil ribonuclease, the S-RNase, which recognizes and rejects incompatible pollen. S-RNases are endocyted by pollen tubes and stored into vacuoles. By a mechanism that is still unknown, these vacuoles are selectively disrupted in incompatible pollen, releasing S-RNases into the cytoplasm and allowing degradation of pollen RNA. Recently, we have studied the timing of in vivo alterations of pollen F-actin cytoskeleton after incompatible pollinations. Besides being essential for pollen growth, F-actin cytoskeleton is a very dynamic cellular component. Changes in F-actin organization are known to be capable of transducing signaling events in many cellular processes. Early after pollination, F-actin showed a progressive disorganization in incompatible pollen tubes. However by the time the F-actin was almost completely disrupted, the large majority of vacuolar compartments were still intact. These results indicate that in incompatible pollen tubes F-actin disorganization precedes vacuolar disruption. They also suggest that F-actin may act as an early transducer of signals triggering the rejection of incompatible pollen.     

蔷薇科植物S-RNase特异性区域分析

S-RNase在配子体型自交不亲和性反应中起关键作用,HV区段被认为是雌蕊与花粉间特异识别的关键部位。应用生物信息学方法,对蔷薇科植物的S-RNase序列分析,并对HV区段一级结构邻近区和空间邻近区作物理化学性质分析,发现HV区C端的一段氨基酸序列符合蛋白质相互作用位点的特征;HVP区也是一个多态性区段,可能参与分子识别过程。因此,蔷薇科植物中,S-RNase与花粉S基因产物的作用方式可能为S-RNase的HVC区与花粉S基因产物先非特异性结合,再以HV区和HVP区进行分子间特异识别。