Pantranscriptome combined with phenotypic quantification reveals germplasm kinship and regulation network of bract color variation in Bougainvillea

Abstract

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.

Integrated metabolome, full‐length sequencing, and transcriptome analyses unveil the molecular mechanisms of color formation of the canary yellow and red bracts of Bougainvillea × buttiana ‘Chitra’

“…The second‐generation sequencing technique was mainly used in the molecular mechanism research of the formation of Bougainvillea flower and bract color at present (Huang et al., 2022). However, second‐generation sequencing has disadvantages such as long sequencing time, short sequence fragments, and poor end quality, which leads to obvious defects in analysis results (Dorado et al., 2021).…”

“…Co-existence of betaxanthins and betacyanins in bracts could produce varied hues of red (Wu et al, 2022). Huang et al (2022) screened some core genes, such as GERD (Germacrene D synthase), SGR (Stay-green protein), ABCA3 (ATP-binding cassette, subfamily A and member 3), GST (Glutathione S-transferase), CYP76C (Cytochrome P450 76 T24-like), and JAZ (Jasmonate ZIM domain-containing protein), associating with bract color variation through pantranscriptome method. However, the bract color formation mechanism of Bougainvillea is still unclear.…”

“…Bougainvillea is a popular horticultural plant in the world and is widely planted in a variety of gardens and landscapes due to its long flowering period and colorful bracts (Saleem et al., 2021; Tsai et al., 2005). Bougainvillea cultivars often contained a wide range of colors, such as purple, red, pink, orange, yellow, white, bicolored, and various shade colors deriving from these series (Huang et al., 2022). The diversified bract colors constituted the rich ornamental characteristics of Bougainvillea and the diversity of garden applications.…”

Multifunctionality of angiosperm floral bracts: a review

“…2). Bracts of some plants are even bicoloured or multicoloured (Huang et al ., 2022; Baczyński & Claßen‐Bockhoff, 2023); for example, some bracts of Cornus florida (Cornaceae) are pink at the outer portions, grading to whitish in the center. Moreover, bract colour of some plant species varies among ontogenetic stages; for instance, the bracts of Davidia involucrata change from green before anthesis to white during anthesis (Fig.…”