Functional analysis of the Arabidopsis thaliana SBP-box gene SPL3: a novel gene involved in the floral transition.

The isolation and initial characterization of the Arabidopsis thaliana SPL3 gene are described. SPL3 belongs to a gene family encoding putative transcription factors characterized by a conserved DNA-binding domain, the SBP domain. SPL3 transcription is developmentally regulated and is localized mainly in vegetative and inflorescence apical meristems, floral meristems and in leaf and floral organ primordia. SPL3 recognizes a conserved sequence motif in the promoter region of the A. thaliana floral meristem identity gene AP1. Similarly to AP1, constitutive expression of SPL3 results in early flowering. However, constitutive expression of SPL3 in an ap1 mutant background showed that AP1 is not required for the early flowering phenotype of the SPL3 transgenic plants. The function of SPL3 during flowering as well as its possible functional redundancy are discussed.