Diverse angiosperm inflorescence patterns can be attributed to modifications of a few basic plans. Some of these modifications affect genes specifying inflorescence (I) and floral (F) meristem identity. Mutations of the LEAFY gene in Arabidopsis and the FLORICAULA gene in Antirrhinum block or delay the I to F transition so that the terminal (I-1) meristem initiates second order (I-2) meristems rather than floral meristems. These mutants have developmental parallels to Pisum sativum inflorescences where I-1 to I-2 to F transitions reflect the wild type phenotype. A comparison of meristem identity gene function in Pisum, Arabidopsis, and Antirrhinum will address how evolutionary modifications can alter inflorescence architecture. The long term goal of these experiments is to establish the genetic hierarchy regulating inflorescence development in Pisum. This proposal focuses on three meristem identity genes: (1) DET (DETERMINATE), which is hypothesized to be an I-1 identity gene; (2) VEG (VEGETATIVE), which is thought to specify I-2 and/or F meristem identity; and (3) PIM (PROLIFERATING INFLORESCENCE MERISTEM), which appears to assign F identity. Using mutants of these genes, the PI will explore how interactions between meristem identity genes regulate inflorescence deelopment. Interactions with other putative meristem identity genes will be investigated. Image analysis of mutant meristems will be used to ascertain if expression of meristem identity genes and meristem geometry correlate. Finally, cloned Arabidopsis and Antirrhinum meristem identity genes will be used to identify homologous RFLP (restriction fragment length polymorphisms) sequences in Pisum. These RFLPs will be mapped and tested for linkage with genetically identified Pisum meristem identity genes. Homology will be further tested by transformation of Pisum meristem identity mutants with Antirrhinum and Agrobacterium meristem identity genes. Together the proposed genetic, morphological, a nd molecular experiments will ascertain if (and how) similar genes can give rise to both I to F and I-1 to I-2 to F inflorescence patterns.
