Synergistic disruptions in seuss cyp85A2 double mutants reveal a role for brassinolide synthesis during gynoecium and ovule development

Screening of M2 lines representing approximately 5,000 M1 individuals identified mutations that enhance the seuss mutant phenotypic disruptions in ovules and gynoecia; here we describe the phenotype of the sum63 mutant and enhanced disruptions of ovule and gynoecial development in the seu sum63 double mutant. Mapping and genetic complementation tests indicate that sum63 is allelic to CYP85A2 (AT3G30180) a cytochrome p450 enzyme that catalyzes the final steps in the synthesis of the phytohormone brassinolide.Our identification of mutations in CYP85A2 as enhancers of the seuss mutant phenotype suggests a previously unrecognized role for brassinolide synthesis in gynoecial and ovule outer integument development. The work also suggests that seuss mutants may be more sensitive to the loss or reduction of brassinolide synthesis than are wild type plants.SEUSS (SEU) is a member of a family of transcriptional co-regulators that controls a diversity of developmental events in Arabidopsis thaliana [1,2]. SEU is required for repression of AGAMOUS during floral organ identity specification. The SEU protein has been shown to physically interact with members of the MADS domain homeobox transcription factor family as well as other transcriptional co-regulators (LEUNIG (LUG) and LEUNIG_HOMOLOGUE [3-6]). These protein interactions mediate repression of AG transcription through the recruitment of a histone deacetylase protein, as well as components of the mediator complex [4,5,7]. These data taken together support a model in which SEU functions as a bridging protein that enables the recruitment of LUG and associated histone deacetylase activities by DNA binding proteins of the MADS domain family. In this model SEU is required for repression of AG in floral whorls that will give rise to perianth organs where these protein complexes are most active [5].SEU and LUG are also required for development of the medial domain of the gynoecium [8,9]. The medial domain of the Arabidopsis gynoeci