Molecular cloning and potential role of DiSOC1s in flowering regulation in Davidia involucrata Baill.

Davidia involucrata Baill. (dove tree) is unique Tertiary relic plant in China, also known as 'living fossil' and 'giant panda'. The MADS-box family gene SOC1 is involved in the regulatory pathway that integrates flowering signals to promote flowering at the optimal time. In this study, we isolated and identified two dove tree SOC1 homologues, named DiSOC1-a and DiSOC1-b. These two sequences possess highly conserved domains MADS-box and SOC1-motif, as well as the semi-conserved region K-box. DiSOC1-a and DiSOC1-b were expressed at varying levels in all tested tissues of dove tree and shared high levels of expression in the flower buds. The expression tendencies of both genes in bract were initially upward and then downward and were highest in young bracts. Neither DiSOC1-a nor DiSOC1-b was expressed in immature leaves. Proteins encoded by DiSOC1-a and DiSOC1-b were located in the nucleus. In addition, ectopic overexpression of both genes in WT Arabidopsis promoted early flowering and the growth of the main bolt. Taken together, these results suggest that DiSOC1-a and DiSOC1-b are involved in the flowering initiation and the main bolt growth process of dove tree. Our results provide a foundation for horticultural breeding to control flowering time of dove tree.

Multifunctional bracts in the dove tree Davidia involucrata (Nyssaceae: Cornales): rain protection and pollinator attraction.

Although there has been much experimental work on floral traits that are under selection from mutualists and antagonists, selection by abiotic environmental factors on flowers has been largely ignored. Here we test whether pollen susceptibility to rain damage could have played a role in the evolution of the reproductive architecture of Davidia involucrata, an endemic in the mountains of western China. Flowers in this tree species lack a perianth and are arranged in capitula surrounded by large (up to 10 cm x 5 cm) bracts that at anthesis turn from green to white, losing their photosynthetic capability. Flowers are nectarless, and pollen grains are presented on the recurved anther walls for 5-7 days. Flower visitors, and likely pollinators, were mainly pollen-collecting bees from the genera Apis, Xylocopa, Halictus, and Lasioglossum. Capitula with natural or white paper bracts attracted significantly more bees per hour than capitula that had their bracts removed or replaced by green paper. Experimental immersion of pollen grains in water resulted in rapid loss of viability, and capitula with bracts lost less pollen to rain than did capitula that had their bracts removed, suggesting that the bracts protect the pollen from rain damage as well as attracting pollinators.