NFL1, a Nicotiana tabacum LEAFY-like gene, controls meristen initiation and floral structure

The Arabidopsis LEAFY (M) gene product induces cells of the shoot apical me ristem to differentiate into floral primordia by acting as a master regulat or of downstream floral homeotic genes. Tobacco, an allotetraploid, possess es two homologous genes, NFL1 and NFL2, which are 97% identical in amino ac id sequence and share 73% amino acid sequence identity with LFY., In order to test whether the highly conserved tobacco orthologue, NFL1, shares funct ional identity with LFY, we created transgenic tobacco and Arabidopsis plan ts that constitutively express the NFL1 cDNA. Our results indicate that NFL 1 plays a critical role in the allocation of meristematic cells that differ entiate lateral structures such as leaves and branches, thereby determining the architecture of the wild-type tobacco shoot. NFL1 also regulates flora l meristem development and does so through the control of cell proliferatio n as well as cell identity. Surprisingly, unlike ectopic LFY expression, wh ich can act as a floral trigger, ectopic NFL1 expression does not promote s evere precocious flowering in Nicotiana tabacum suggesting that variations in amino acid sequence among members of the LFY-like gene family have led t o divergence in the functional roles of these genes.