Molecular mechanism of interaction between SHORT VEGETATIVE PHASE and APETALA1 in Arabidopsis thaliana.

Point mutations were introduced into specific leucine (L) amino acids within the K domain of SHORT VEGETATIVE PHASE (SVP), and their effects on the SVP-AP1 interaction were assessed. Yeast two-hybrid experiments and β-galactosidase activity assays demonstrated that SVP maintained its capacity to interact with APETALA1 (AP1) despite point mutations at the 108th, 116th, 119th, and 127th leucine residues, where leucine was substituted with alanine (A). However, the mutation of the leucine residue at position 124 to alanine abolished the interaction between SVP and AP1 regardless of whether the mutation was singular or combined with others. Pull-down experiments confirmed that the leucine residue at position 124 is particularly critical for the SVP-AP1 interaction. Arabidopsis plants overexpressing 35S::AtSVP-L124A exhibited a delayed flowering phenotype compared to wild-type Col-0 Arabidopsis plants, but showed early-flowering phenotype compared to SVP overexpressing plants. SVP binds to the promoters of AP1, APETALA3 (AP3), PISTILLATA (PI), and SEPALLATA3 (SEP3), as well as to the intron of AGAMOUS (AG). Through the formation of heterodimers with AP1, SVP regulates the expression of B-class and C-class floral homeotic genes, thereby modulating floral organ development. The leucine residue at position 124 of SVP is essential for its interaction with AP1, and 35S::AtSVP-L124A transgenic plants exhibited an extended period of vegetative growth.