The SERRATE locus controls the formation of the early juvenile leaves and phase length in Arabidopsis

The development of the shoot can be divided into a series of distinct devel opmental phases based on leaf character-istics and inflorescence architectu re. The relationship between phase length, defined by the number of organs produced, and the timing of the floral induction (V-3-I-1 transition) is re latively ill defined. Characterization of the serrate mutant (CS3257; Arabi dopsis Biological Research Center) revealed defects in both vegetative and inflores-cence phase lengths, the timing of phase transitions, leaf number, the leaf initiation rate, and phyllotaxy. The timing of floral induction, however, is the same as in wild-type in extended short days as well as in s hort days, whereas the flowering time response to photoperiod is unaffected . SERRATE is shown to be required for the development of early juvenile lea ves (V-1) and to promote late juvenile leaf development (V-2), while suppre ssing adult leaf (V-3) and inflorescence development (I-1 and I-2). The se mutation supports the hypothesis that the timing of floral induction is ind ependent of vegetative and inflorescence phase lengths. The role of SERRATE in the regulation of phase length and leaf identity is discussed.