Research Institute of Forestry, Chinese Academy of Forestry, Key Laboratory of Tree Breeding and Cultivation of the State Forestry and Grassland Administration, Beijing 100091, China; Hazelnut Engineering and Technical Research Center of the State Forestry and Grassland Administration, Beijing 100091, China; National Hazelnut Industry Innovation Alliance, Beijing 100091, China.
Research Institute of Forestry, Chinese Academy of Forestry, Key Laboratory of Tree Breeding and Cultivation of the State Forestry and Grassland Administration, Beijing 100091, China; Hazelnut Engineering and Technical Research Center of the State Forestry and Grassland Administration, Beijing 100091, China; National Hazelnut Industry Innovation Alliance, Beijing 100091, China.
Gene. 2020 Sep 25;756:144917. doi: 10.1016/j.gene.2020.144917. Epub 2020 Jun 23.
The self-incompatibility system of Corylus is a sporophytic type that is phenotypically similar to that of Brassica. While the molecular mechanism of sporophytic self-incompatibility (SSI) has been investigated extensively in Brassica (Brassicaceae), little is known about the corresponding mechanism in Corylus (Betulaceae). Here, we discuss the SSI mechanism with respect to S-locus receptor kinase (SRK) gene homologs. To obtain two SRK candidate unigenes, we compared all of the unigenes in a transcriptional protein database from our previous study with BnSRK-1 (AB270767) using BLASTX with a cutoff e-value of 10. We then cloned the full-length cDNA of ChaSRK1 and ChaSRK2 genes from Ping'ou hybrid hazelnut (Corylus heterophylla × Corylus avellana) using RACE techniques. Bioinformatics approaches were used to analyze the cDNA sequences, protein sequences, and domains of the encoded proteins. The full-length ChaSRK1 cDNA was 2883 base pairs (bp) with a coding sequence (CDS) of 2,547 bp encoding 849 amino acid residues. The full-length ChaSRK2 cDNA was 2,693 bp, with a CDS of 2,433 bp encoding 811 amino acids. The ChaSRK1/2 proteins contained an S-domain (extracellular domain), a transmembrane domain, a Ser/Thr protein kinase active site (kinase domain), and DUF3660 and/or DUF3403 domains. The lengths of 18 partial SRK homologs ranged from 1347 to 1451 bp, and they contained the same structural domains as ChaSRK1 and ChaSRK2. Phylogenetic analysis revealed that all SRK homologs could be divided into two categories that were similar to the classification of SRKs in Brassica. The expression patterns of ChaSRK1 and ChaSRK2 differed: ChaSRK2 was predominantly expressed in mature stigmatic styles, while ChaSRK1 was expressed in other tissues with the highest in the root tips of Corylus. Using dual-color fluorescence in situ hybridization, ChaSRK1/2 expression was found to be localized in papillar cells. Collectively, these results revealed that SRKs from Corylus had similar characteristics to SRKs from Brassica. We therefore speculated that the SSI mechanism in Corylus might be more similar to the Brassica mechanism than to other SSI types.
核桃的自交不亲和性系统是一种孢子体型，表型上与芸薹属（Brassica）相似。虽然芸薹属（十字花科）的孢子体型自交不亲和性（SSI）的分子机制已得到广泛研究，但对于核桃（桦木科）的相应机制知之甚少。在这里，我们根据 S 座位受体激酶（SRK）基因同源物讨论 SSI 机制。为了获得两个 SRK 候选基因，我们使用 BLASTX 比较了之前研究中转录蛋白数据库中的所有基因与 BnSRK-1（AB270767）的同源性，使用的截断 e 值为 10。然后，我们使用 RACE 技术从平欧杂种榛（Corylus heterophylla×Corylus avellana）中克隆了 ChaSRK1 和 ChaSRK2 基因的全长 cDNA。生物信息学方法用于分析 cDNA 序列、蛋白质序列和编码蛋白的结构域。ChaSRK1 cDNA 全长 2883 个碱基对（bp），编码序列（CDS）为 2547 bp，编码 849 个氨基酸残基。ChaSRK2 cDNA 全长 2693 bp，CDS 为 2433 bp，编码 811 个氨基酸。ChaSRK1/2 蛋白包含 S 结构域（细胞外结构域）、跨膜结构域、丝氨酸/苏氨酸蛋白激酶活性位点（激酶结构域）以及 DUF3660 和/或 DUF3403 结构域。18 个部分 SRK 同源物的长度范围为 1347 至 1451 bp，它们包含与 ChaSRK1 和 ChaSRK2 相同的结构域。系统发育分析表明，所有 SRK 同源物可分为两类，与芸薹属 SRK 的分类相似。ChaSRK1 和 ChaSRK2 的表达模式不同：ChaSRK2 主要在成熟的柱头中表达，而 ChaSRK1 在其他组织中表达，在根尖端的表达最高。使用双色荧光原位杂交，发现 ChaSRK1/2 表达定位于乳突细胞中。总之，这些结果表明，来自核桃的 SRK 具有与来自芸薹属的 SRK 相似的特征。因此，我们推测核桃的 SSI 机制可能与芸薹属的机制更为相似，而不是与其他 SSI 类型相似。
