苞片是被子植物中的变态非花器官。发现片的颜色和形状的变化是新官能化的(即,类似于花瓣),作为传粉媒介吸引子获得研究兴趣。九重葛以其专业而闻名,大,和五颜六色的苞片,与它微小的无色花朵形成对比。作为一种在颜色方面差异很大的植物,九重葛片着色和多色性的分子机制在很大程度上是未知的。九重葛缺乏基因组信息在很大程度上阻碍了对片叶颜色变异的进化和遗传基础的研究。在这项研究中,从18个九重葛种质中获得的片的全转录组用于研究全球种群水平的种质亲属关系和片颜色变异的基因调控网络。我们的结果表明,B.glabra种质的the片在很大程度上区分了国际照明委员会(CIE)L-a-b值。此外,利用主成分分析检测种质亲缘关系,系统发育,混合分析显示了三个最优子群,其中两个明显聚集,在种群水平上与苞片颜色变化没有直接相关。高与高之间的差异表达基因(DEGs)较低的L-a-b值揭示了与片颜色L-a-b变异有关的几个相当大的上调基因。构建了加权基因共表达网络,并确定了八个共表达的调节模块,这些模块与bractCIEL-a-b颜色值的变化高度相关。几个候选DEGs和共表达的hub基因(例如,GERD,SGR,ABCA3,GST,CYP76AD1,CYP76C,和JAZ)与苞片颜色变化密切相关,最终确定负责L-a-b着色,这可能是导致B.glabra片颜色变化的核心调节因素。本研究为种质亲属关系的研究提供了有价值的见解,群体水平的泛转录组表达谱,以及园艺九重葛关键创新片颜色变化的分子基础。
Bracts are the metamorphic non-flower organ in angiosperm plants. The variation of the color and shape of bracts was found to be neo-functionalized (i.e., similar to petals), garnering research interest as a pollinator attractor. Bougainvillea is known for its specialized, large, and colorful bracts, which contrast with its tiny colorless flowers. As a plant whose bracts vary greatly in terms of coloration, the molecular mechanisms for Bougainvillea bract coloration and polychroism are largely unknown. The lack of genomic information for Bougainvillea largely hinders studies into the evolution and genetic basis of bract color variation. In this study, a pan-transcriptome of bracts obtained from 18 Bougainvillea glabra accessions was employed to investigate the global population-level germplasm kinship and the gene regulation network for bract color variation. Our results showed that the bracts of B. glabra accessions have largely differentiated International Commission on Illumination (CIE) L-a-b values. Moreover, germplasm kinship detected using principal component analysis, phylogeny, and admixture analysis showed three optimal subgroups, two of them distinctly clustered, which were not directly correlated with bract color variation at the population level. Differentially expressed genes (DEGs) between accessions of high vs. low L-a-b values revealed several considerable upregulated genes related to bract color L-a-b variation. A weighted gene co-expression network was constructed, and eight co-expressed regulation modules were identified that were highly correlated with variation in bract CIE L-a-b color values. Several candidate DEGs and co-expressed hub genes (e.g., GERD, SGR, ABCA3, GST, CYP76AD1, CYP76C, and JAZ) that were tightly associated with bract color variation were eventually determined responsible for L-a-b colorations, which might be the core regulation factors contributing to the B. glabra bract color variation. This study provides valuable insights into the research on germplasm kinship, population-level pan-transcriptome expression profiles, and the molecular basis of color variation of key innovative bracts in horticultural Bougainvillea.