Poster: Cell division

Abs # 674: Isolation and characterization of siamese phenotypic modifiers

Presenter:	Kasili, Remmy W., rkasil1@lsu.edu
Authors	Kasili, Remmy W. (A)   Walker, Jason D. (B)   Larkin, John C (A)
Affiliations:	(A): Louisiana State University, Dept. of Biological Sciences (B): Yale University, Dept. of Genetics

Arabidopsis trichomes (leaf hairs) are cells that extend from the epidermis of leaves and sepals. They are a well established model for the study of cell differentiation because they are large and easily visible, making it easy to identify mutant phenotypes. During development, wild type (WT) Arabidopsis trichomes exit the mitotic cycle and enter an endoreplication cycle. Here DNA replication occurs without nuclear and cellular division resulting in cells with DNA content that is more than 2C. This mitosis-endoreplication switch is an integral part of the trichome differentiation programme. The siamese (sim) mutation is a recessive mutation that produces multicellular trichomes. The sim mutation appears to trigger extra rounds of cell division in mutant trichomes that is not observed in WT trichomes, suggesting that the gene encodes a cell cycle regulator. It is likely that the SIAMESE (SIM) gene product interacts with other cell cycle components. Phenotypic modifiers have been used to identify genes functioning together in the same pathway or to indicate that gene products interact. We mutagenized homozygous sim seeds with ethyl methane sulfonate (EMS) and examined seedlings from M2 seeds for alteration of the sim multicellular paired trichome phenotype by new mutations. In particular, several alleles have been recovered at a locus that, when mutant strongly enhances the multicellularity of sim homozygotes. We present here phenotypic characterization of this locus and other modifiers recovered from the screen.