Mechanism and biological function of the regulation of cellulose synthesis by light

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Cellulose is the most abundant biopolymer on earth and becomes increasingly studied in basic and applied plant research to promote future industrial applications such as second generation biofuels. In Arabidopsis, primary cellulose is produced by the hexameric cellulose synthase complex that is composed of the cellulose synthases (CESA) 1, 3 and 6 and localizes to the plasma membrane. Mutants in CESA6 show growth defects and cellulose deficiency in the dark-, but not in the light grown hypocotyl. We hypothesize that the rescue of these phenotypes in light is the result of the presence of a light-activated CESA6-related isoform, which might be phosphorylated CESA5. Experimental goals of the present proposal are (1) to analyze the regulation of CESA5 by light, its presence in the primary cellulose synthase complex, its plasma membrane motility and intracellular trafficking by confocal spinning disk microscopy, (2) to link the activation of CESA5 by light to phytochrome-induced phosphorylation by analyzing its phosphorylation state and activity by respectively mass spectrometry and spinning disk microscopy, and (3) to clarify the possible role of CESA5 in quality control of cellulose microfibrils by various microscopy methods and to identify its molecular partners.