Light-induced gene-specific expression of the Lhc gene family in Arabidopsis thaliana and their regulation by transcription and translation
Final Report Abstract
At three levels of light intensity, the influence of the red (R) to far-red (FR) light ratio on the gene expression of light-harvesting complex (Lhc) genes in Arabidopsis thaliana was investigated simulating the situation at noon or under a leaf canopy. In a short term experiment during greening the possible effect of phytochrome on the expression of 17 Lhc genes was tested in the wild types Columbia and Landsberg erecta, and in the phytochrome mutants phyAB, and phyBDE. Moreover, the expression of the plastidic genes psaA and psbA were investigated under the same light conditions. In all experiments, the mRNA levels of the investigated Lhc genes were only slightly influenced by light intensity or the R to FR ratio. Lhcb1.4, however, responded differently as increasing FR intensity down-regulated the mRNA level. The plastidic gene psbA was regulated by phytochrome A alone and the expression level increased with increasing FR intensity. PsaA responded also to light intensity and the R to FR ratio but this effect was not mediated by phytochrome. In a long-term experiment, the possible regulation of Lhc gene expression by light was investigated in seedlings after greening. Analysis of the gene expression of the mutants phyA, phyBDE, AYH and BYH (expression of constitutively active phytochrome A or B, respectively) results in the following conclusions: (1.) Phytochrome B mediates the up-regulation of the Lhc gene expression in R light. (2.) Phytochrome B acts against a strong decrease of the Lhc mRNA level in FR light. In general, no distinct expression reaction patterns for the different Lhc subfamilies toward light intensity or light quality were found. However, within subfamilies and even closely related Lhc genes may show very different responses. Es an example, whereas Lhcb1.4 mRNA is strongly down-regulated by increasing FR irradiation, this is not the case at all for Lhcb1.5.
