The effect of the floral repressor FLC on the timing and progression of vegetative phase change in Arabidopsis

Plants undergo two major post-embryonic developmental transitions - the juvenile-to-adult vegetative transition (vegetative phase change) and the adult-to-reproductive transition (flowering). In woody plants, these transitions can be separated by years, but in herbaceous species they are often very close together, making it difficult to differentiate the effects of vegetative phase change and floral induction on vegetative development. To distinguish between these factors, we have compared the vegetative morphology of plants highly expressing the floral repressor FLC (FRI;FLC) with plants mutant for this gene (FRI;flc-3) under both photoinductive (long day, LD and night interruption, NI) and non-photoinductive (short day, SD) conditions. We show that the onset of abaxial trichome production is insensitive to floral induction, but the distribution and overall number of abaxial trichomes, as well as several other leaf traits associated with vegetative change, are strongly influenced by flowering. Most of the major differences in leaf morphology between FRI; FLC and FRI; flc-3 plants grown in LD can be attributed to the early flowering phenotype of FRI; flc-3, because these differences are not apparent in plants grown in SD. These include differences in leaf size, hydathode number and the distribution of abaxial trichomes along the length of the leaf. Leaf shape and the total number of abaxial trichomes are affected by FLC independently of its effect on flowering. Our results demonstrate that the onset and the progression of vegetative phase change are regulated by different combinations of endogenous and environmental factors, and reveal a role for FLC in vegetative development.