Table_1_Transcriptomes Divergence of Ricotia lunaria Between the Two Micro-Climatic Divergent Slopes at “Evolution Canyon” I, Israel.xlsx

As one of the hotspot regions for sympatric speciation studies, Evolution Canyon (EC) became an ideal place for its high level of microclimatic divergence interslopes. In this study, to highlight the genetic mechanisms of sympatric speciation, phenotypic variation on flowering time and transcriptomic divergence were investigated between two ecotypes of Ricotia lunaria, which inhabit the opposite temperate and tropical slopes of EC I (Lower Nahal Oren, Mount Carmel, Israel) separated by 100 m at the bottom of the slopes. Growth chamber results showed that flowering time of the ecotype from south-facing slope population # 3 (SFS 3) was significantly 3 months ahead of the north-facing slope population # 5 (NFS 5). At the same floral development stage, transcriptome analysis showed that 1,064 unigenes were differentially expressed between the two ecotypes, which enriched in the four main pathways involved in abiotic and/or biotic stresses responses, including flavonoid biosynthesis, α-linolenic acid metabolism, plant–pathogen interaction and linoleic acid metabolism. Furthermore, based on Ka/Ks analysis, nine genes were suggested to be involved in the ecological divergence between the two ecotypes, whose homologs functioned in RNA editing, ABA signaling, photoprotective response, chloroplasts protein-conducting channel, and carbohydrate metabolism in Arabidopsis thaliana. Among them, four genes, namely, SPDS1, FCLY, Tic21 and BGLU25, also showed adaptive divergence between R. lunaria and A. thaliana, suggesting that these genes could play an important role in plant speciation, at least in Brassicaceae. Based on results of both the phenotype of flowering time and comparative transcriptome, we hypothesize that, after long-time local adaptations to their interslope microclimatic environments, the molecular functions of these nine genes could have been diverged between the two ecotypes. They might differentially regulate the expression of the downstream genes and pathways that are involved in the interslope abiotic stresses, which could further diverge the flowering time between the two ecotypes, and finally induce the reproductive isolation establishment by natural selection overruling interslope gene flow, promoting sympatric speciation.

作为同域物种形成研究的热点区域之一，进化峡谷（Evolution Canyon，EC）因其坡间极高的微气候分化程度，成为该领域理想的研究场所。本研究为揭示同域物种形成的遗传机制，对栖息于以色列卡梅尔山下纳哈尔奥伦峡谷I号（EC I）相反的温带坡与热带坡（两坡底部间距100米）的香屈曲花（Ricotia lunaria）两种生态型的开花时间表型变异与转录组分化展开了调查。人工气候室实验结果显示，来自南坡种群3（SFS 3）的生态型，其开花时间较北坡种群5（NFS 5）显著提前3个月。在相同花发育阶段开展的转录组分析表明，两种生态型间共有1064个单基因（unigene）存在差异表达，这些差异基因富集于4条主要的非生物与/或生物胁迫响应通路，包括类黄酮生物合成、α-亚麻酸代谢、植物-病原体互作以及亚油酸代谢。此外，通过Ka/Ks分析，本研究推测有9个基因参与了两种生态型间的生态分化；这些基因在拟南芥（Arabidopsis thaliana）中的同源基因功能涉及RNA编辑、脱落酸（ABA）信号通路、光保护响应、叶绿体蛋白转运通道以及碳水化合物代谢。其中，SPDS1、FCLY、Tic21和BGLU25这4个基因还在香屈曲花与拟南芥间呈现适应性分化，表明这些基因可能在植物物种形成过程中发挥重要作用，至少在十字花科（Brassicaceae）植物中如此。基于开花时间表型与比较转录组的研究结果，我们提出如下假说：在长期适应坡间微气候环境后，这9个基因的分子功能在两种生态型间已发生分化。它们可能差异调控参与坡间非生物胁迫的下游基因与通路的表达，进而进一步拉大两种生态型间的开花时间差异，并最终通过自然选择凌驾于坡间基因流之上建立生殖隔离，从而促进同域物种形成。