PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

Genes for the regulation of the light-harvesting chlorophyll antenna size in Chlamydomonas reinhardtii. Anastasios Melis^*,1, Juergen Polle¹, Sarada-Devi Kanakagiri¹, ¹ UC Berkeley, Berkeley, CA, USA

ABSTRACT- DNA insertional mutagenesis and screening of the green alga Chlamydomonas reinhardtii was employed to isolate tla1, a stable transformant having a down-regulated light-harvesting chlorophyll antenna size. The gene responsible for this down-regulation, a first of its kind, was cloned and its structural and functional properties were investigated: Molecular analysis showed a single plasmid insertion into an ORF of the nuclear genome corresponding to a novel gene (Tla1) that encodes a protein of 213 amino acids. Genetic analysis showed co-segregation of plasmid and tla1 phenotype. Biochemical analyses showed the tla1 mutant to be chlorophyll deficient, with a functional chlorophyll antenna size of photosystem-II and photosystem-I being about 50% and 65% of the wild type, respectively. It contained a correspondingly lower amount of light-harvesting proteins than the wild type and had lower steady state levels of Lhcb mRNA. The tla1 strain required a higher light intensity for the saturation of photosynthesis and showed greater solar conversion efficiencies and a higher photosynthetic productivity than the wild type under mass culture conditions. Sequence analysis revealed unique features and suggested a novel gene-expression regulatory pathway for the Tla1 protein. Results are discussed in terms of the tla1 mutation, its phenotype, and the functional role-played by the Tla1 gene in the regulation of the photosynthetic chlorophyll antenna size in Chlamydomonas reinhardtii.

KEY WORDS: Chlorophyll antenna size, Solar conversion efficiency, DNA insertional mutagenesis , Regulation