Dynamic transcriptomic features accompanying the onset of first flowering in roses

Onset time of the first flowering is pivotal for the reproductive success of perennial polycarpic plants especially in woody species, like roses. Despite the key innovation of continuous flowering in some roses, little is known about the molecular features underlying the onset of their first flowering due, in large part, to the difficulties in the promotion and synchronization of seed germination.

In this study, we optimized a germination procedure to explore the dynamic transcriptomic features along seedling establishment through the first flowering in a rose line, Rosa 'Yann Arthus-Bertrand'. Low temperature treatments at 5 °C or 10 °C for three or four months significantly enhance germination rates up to 60%. We then generated leaf transcriptomes for five developmental stages with 10,353 differentially expressed genes from germination through flowering. Flowering genes involved in aging together with the photoperiod-circadian-clock, gibberellins and autonomous pathways were expressed differentially and stepwise along developmental stages, indicating their potential roles in the regulation of first flowering. Via phylogenetic clustering and expression analyses together with heterologous expression approaches in Arabidopsis, we revealed that rose SQUAMOSA PROMOTER BINDING PROTEIN-LIKE3/4/5 (SPL3/4/5) genes were potential regulators of seedling growth and flowering.

By offering a dynamic expression profile, our study identifies those transcriptomic features that provide novel insights into the molecular pathways regulating the onset of first flowering in roses, one of the most important horticultural plants, and in woody plants in general.