Palumbo Fabio, Draga Samela, Magon Gabriele, Gabelli Giovanni, Vannozzi Alessandro, Farinati Silvia, Scariolo Francesco, Lucchin Margherita, Barcaccia Gianni
Department of Agronomy, Food, Natural resources, Animals and Environment (DAFNAE), University of Padua, Padua, Italy.
Front Plant Sci. 2023 Jun 2;14:1204538. doi: 10.3389/fpls.2023.1204538. eCollection 2023.
The genus offers a unique opportunity to study the sporophytic self-incompatibility (SSI) system, being composed of species characterized by highly efficient self-incompatibility (e.g., ) and complete self-compatibility (e.g., ). To this end, the chicory genome was used to map seven previously identified SSI locus-associated markers. The region containing the S-locus was therefore restricted to an ~4 M bp window on chromosome 5. Among the genes predicted in this region, () was particularly promising as a candidate for SSI. Its ortholog in Arabidopsis ( is involved in pollen-stigma recognition reactions, and its protein structure is similar to that of S-receptor kinase (SRK), a key component of the SSI system in the genus. The amplification and sequencing of in chicory and endive accessions revealed two contrasting scenarios. In , was fully conserved even when comparing different botanical varieties (i.e., smooth and curly endive). In , 387 polymorphic positions and 3 INDELs were identified when comparing accessions of different biotypes all belonging to the same botanical variety (i.e., radicchio). The polymorphism distribution throughout the gene was uneven, with hypervariable domains preferentially localized in the LRR-rich extracellular region, putatively identified as the receptor domain. The gene was hypothesized to be under positive selection, as the nonsynonymous mutations were more than double the synonymous ones (dN/dS = 2.17). An analogous situation was observed when analyzing the first 500 bp of the promoter: no SNPs were observed among the endive samples, whereas 44 SNPs and 6 INDELs were detected among the chicory samples. Further analyses are needed to confirm the role of MIK2 in SSI and to demonstrate whether the 23 species-specific nonsynonymous SNPs in the CDS and/or the species-specific 10 bp-INDEL found in a CCAAT box region of the promoter are responsible for the contrasting sexual behaviors of chicory and endive.
该属为研究孢子体自交不亲和（SSI）系统提供了独特的机会，它由具有高效自交不亲和特性的物种（如……）和完全自交亲和的物种（如……）组成。为此，利用菊苣基因组对7个先前鉴定的与SSI位点相关的标记进行定位。因此，包含S位点的区域被限制在5号染色体上约4兆碱基对的窗口内。在该区域预测的基因中，（……）作为SSI的候选基因特别有前景。其拟南芥直系同源基因（……）参与花粉 - 柱头识别反应，其蛋白质结构与S受体激酶（SRK）相似，SRK是该属SSI系统的关键组成部分。菊苣和苦苣材料中该基因的扩增和测序揭示了两种截然不同的情况。在苦苣中，即使比较不同的植物变种（即光滑叶和皱叶苦苣），该基因也完全保守。在菊苣中，当比较属于同一植物变种（即红菊苣）的不同生物型的材料时，鉴定出387个多态性位点和3个插入缺失。整个基因的多态性分布不均匀，高变区优先定位在富含亮氨酸重复序列（LRR）的细胞外区域，推测该区域为受体结构域。该基因被假定处于正选择之下，因为非同义突变是同义突变的两倍多（dN/dS = 2.17）。在分析该基因启动子的前500 bp时也观察到类似情况：苦苣样品中未观察到单核苷酸多态性（SNP），而菊苣样品中检测到44个SNP和6个插入缺失。需要进一步分析以确认MIK2在SSI中的作用，并证明编码区中的23个物种特异性非同义SNP和/或在启动子的CCAAT框区域中发现的物种特异性10 bp插入缺失是否导致菊苣和苦苣不同的有性生殖行为。
