PNNL

Abstract

The unicellular green alga Chlamydomonas reinhardtii displays metabolic flexibility in response to a changing environment. We analyzed expression patterns of its three genomes in cells grown under light-dark cycles. Nearly 85% of transcribed genes show differential expression, with different sets of transcripts being up-regulated over the course of the day to coordinate cellular growth before undergoing cell division. Parallel measurements of select metabolites and pigments, physiological parameters and a subset of proteins allow us to infer metabolic events and to evaluate the impact of the transcriptome on the proteome. Among new findings are the observations that Chlamydomonas exhibits lower respiratory activity at night compared to the day; multiple fermentation pathways, some oxygen-sensitive, are expressed at night in aerated cultures; we propose that the ferredoxin FDX9 is potentially the electron donor to hydrogenases. The light stress responsive genes PSBS, LHCSR1 and LHCSR3 show an acute response to lights-on at dawn under abrupt dark-to-light transitions while LHCSR3 genes also exhibits a later, second burst in expression in the middle of the day dependent on light intensity. Each response to light (acute and sustained) can be selectively activated under specific conditions. Our expression dataset, complemented with co-expression networks and metabolite profiling, should constitute an excellent resource for the algal and plant communities.