RUI: Molecular Genetic Analysis of Chlorophyll b Synthesis in Arabidopsis

California State University-Long Beach, Long Beach CA

Investigators

Abstract

Chlorophyll (Chl) b binds and stabilizes the light harvesting complex proteins of photosystem II in vascular and non-vascular plants, green algae and prochlorophytes. Chl b is synthesized from Chl a in a reaction that requires chlorophyll a oxygenase, the product of the Arabidopsis AtCAO gene. This project will yield transgenic plants that overexpress AtCAO in order to observe if the stable ratio of Chl a to Chl b can be perturbed. Plants with constitutive and inducible promoters will be produced, AtCAO mRNA and protein level will be measured, and rates of Chl b synthesis will be determined. The phenotypes of overproducing lines will be examined to determine if an extra large PSII light harvesting complex is formed. The second objective will be the production of an AtCAO antibody for measurement of protein levels and for suborganelle localization by immunogold labeling. The third objective concerns a mutant, conditional chlorina, that has decreased levels of Chl, especially Chl b, under moderate light intensity. This line appears yellow-green under moderate light intensity, and this visible phenotype correlates to partial loss of Lhcb proteins located in the inner and outer antenna complex. This line has been used to screen for mutants that turn less yellow-green under moderate light intensity, cch suppressors. One of these suppressor lines has been shown to have a phenotype that is visible during segregation of the F2. Characterization and mapping of this, and other suppressors, are proposed. The final objective is to initiate a new project in the laboratory; an analysis of the very high-light responsive promoters of the nuclear Elip1 and Elip2 genes. Both Elip genes are induced 100-fold after four hours at very high light intensity. These studies could lead to an understanding of the factors that are required for the exciton-dissipating chloroplast to communicate with the nucleus. Along with furthering knowledge about the regulation and localization of Chl b synthesis, and chloroplast-nuclear communication, talented undergraduate and Masters degree students, many of them from minorities that are underrepresented in the sciences, will receive training for research careers.