The role of membrane proteins in Arabidopsis seedling development

To identify genes that are regulated by phytochrome A (phyA) during far-red light (FR) induced de-etiolation a transcriptomics approach was used. Transporter genes from a range of transport classes were identified using both the Arabidopsis membrane Transporter (AMT) array and data from previous published array densities. Examples of FR-light induced genes included the monosaccharide transporter STP1, a Ca²⁺ ATPase, ACA2, the auxin transporter PIN4, a putative anthocyanins transporter ANM2 and two genes of unknown function, the Niemann-Pick C disease-like protein and FRIMP1. Three FR-light repressed candidate transporter genes were also selected, RAN1 an ATP-dependent copper transporter, CAT4 an amino acid transporter and AHA2 an H⁼-ATPase. Most of the genes were confirmed as being FR-light regulated by FR-light using RT-PCR and real-time PCR. The expression of some genes, including STP1 was also shown to be mediated by other wavelengths of light including blue and red-light. To further study the role of these candidate genes in seedling de-etiolation insertional T-DNA mutants were obtained and characterised. The stp1, aca2, cat4 and aha2 mutants were obtained and interesting phenotypes were shown in some of these mutants. This included a reduced apical hook curvature and a reduction in hypocotyls elongation in the dark-grown cat4 mutant and a smaller aca2 seedling when grown in blue and white-light. A gene of unknown function was also established as being FR-light induced and termed FRIMP (Far-red Induced Membrane Protein). The frimp1 mutant had a number of phenotypic characteristics including the epinastic curling of the leaves, elongated petioles and an elongated hypocotyl in the FR-light grown seedling.