Poster: Organelle Biogenesis

Abs # 1166: Identification of the genetic requirements for light-dependent chlorophyll biosynthesis and coupled plastid differentiation in green plants

Presenter:	Armstrong, Gregory A, armstrong.275@osu.edu
Authors	Armstrong, Gregory A (A)   Su, Qingxiang  (B)   Apel, Klaus  (B)   Frick, Geneviève  (B) (C)
Affiliations:	(A): Department of Plant Biology, Ohio State University (B): Institute for Plant Sciences, Plant Genetics, Swiss Federal Institute of Technology (ETH), Zürich, Switzerland (C): Swiss Federal Research Station for Animal Production, Posieux, Switzerland
Web Site:	http://www.biosci.ohio-state.edu/~plantbio/Faculty/facultymain.htm

A key reaction in the biosynthesis of chlorophylls (Chls) a and b from cyanobacteria through higher plants is the strictly light-dependent reduction of protochlorophyllide (Pchlide) a to chlorophyllide a. Angiosperms, unlike other photosynthetic organisms, rely exclusively upon this mechanism to reduce Pchlide and hence require light to green. In Arabidopsis light-dependent Pchlide reduction is mediated by three structurally related but differentially regulated NADPH:Pchlide oxidoreductases, denoted PORA, PORB and PORC. The PORA and PORB genes, but not PORC are strongly expressed early in seedling development. In contrast, expression of PORB and PORC, but not PORA, is readily detectable in older seedlings and adult plants. We have tested the hypothesis that PORB and PORC govern light-dependent Chl biosynthesis throughout most of plant development by identifying porB and porC mutants of Arabidopsis, the first higher plant por mutants characterized, in which the corresponding genes are interrupted by a derivative of the maize Dissociation transposable element. Single por mutants grown photoperiodically display no obvious phenotypes at the whole plant or chloroplast ultrastructural levels, although the porB-1 mutant does exhibit severely impaired etioplast inner membrane formation. In contrast, a light-grown porB-1 porC-1 double mutant develops a seedling-lethal xantha phenotype at the cotyledon stage, contains only small amounts of Chl a, and displays reduced thylakoid membrane stacking. Thus, the presence of either PORB or PORC seems to be a prerequisite for light-dependent chloroplast differentiation, and for plant growth and development. Frick, G., Su, Q., Apel, K. & G.A. Armstrong (2003) Plant J., in press.