Minisymposium 17: Evolution of Plant Development

Abs # 31002: COCHLEATA and PIM redundantly regulate floral meristem identity in Pisum sativum

Presenter:	Singer, Susan R, ssinger@carleton.edu
Authors	Singer, Susan R (A)   Maki, Sonja L (A)   Stock, Suzanne  (A)   Dozier, Melissa  (A)   Peterson, Soren  (A)   Mullen, H  (A)
Affiliations:	(A): Department of Biology, Carleton College, Northfield, MN 55057
Web Site:	http://www.acad.carleton.edu/curricular/BIOL/faculty/ssinger/

Flowering genes are highly conserved in the angiosperms and our interest is in how orthologs are used in different species to give rise to distinctive inflorescence architectures. Our approach is to identify Pisum sativum (garden pea) orthologs of well characterized Arabidopsis genes and correlate the cloned genes with known mutant phenotypes. Pea is an excellent model system because its inflorescence is one step more complex than that of Arabidopsis. Flowers form from the third rather than the second order axillary meristems of the inflorescence. Our research focuses on two floral meristem identity genes. COCHLEATA (COCH) affects the transition to flowering, pod development and symmetry in both leaf stipules and floral parts, while PROLIFERATING INFLORESCENCE MERISTEM (PIM) regulates the floral transition in pea. PIM is the ortholog of AP1 (Taylor et al. 2002. Plant Physiol.129, 1150.) Here we report that COCH and PIM redundantly function as floral meristem identity genes in pea. The loss of function of both genes completely blocks the floral transition. We have anlayzed double mutants of four COCH alleles, coch-w, coch-p, coch, and coch- het, in combination with pim-1, a large deletion mutation. The interactions range from complete suppression of floral meristem development (coch-w pim-1) to the loss of second order inflorescence (I2) bract suppression, resulting in compound leaves on the I2 (coch-het pim-1). While compound leaves develop on the main axis of the inflorescence of wild type, nearly total bract supression is observed on I2 branches. We have followed the crosses between COCH alleles and pim-1 through the F4 generation and find the expected ratios for two recessive alleles that are not linked. In one study, coch pim-1 plants segregated into early and late flowering backgrounds. Only a small delay in flowering is expected in otherwise wild-type late flowering lines under long day conditions, but late flowering lines of coch pim-1 could not initiate floral meristems even after producing 120 nodes. Those lines that flowered had clustered inflorescences with almost no internode elongation. Flowering was variable in coch-p pim-1 plants, but the variability does not appear to correspond to segregating floral time genes. We are continuing to pursue an explanation for this variable phenotype. In all our double mutants, carpels were absent, a more extreme phenotype than seen in pim-1 or any of the COCH alleles. Supported by NSF 9977087.