Phytochrome A Mediates Blue Light and UV-A-Dependent Chloroplast Gene Transcription in Green Leaves

Abstract

We characterized the photobiology of light-activated chloroplast transcription and transcript abundance in mature primary leaves by using the following two systems: transplastomic promoter-reporter gene fusions in tobacco (Nicotiana tabacum), and phytochrome (phyA, phyB, and hy2) and cryptochrome (cry1) mutants of Arabidopsis. In both dicots, blue light and UV-A radiation were the major signals that activated total chloroplast and psbA, rbcL, and 16S rrn transcription. In contrast, transcription activities in plants exposed to red and far-red light were 30% to 85% less than in blue light/UV-A, depending on the gene and plant species. Total chloroplast, psbA, and 16S rrn transcription were 60% to 80% less in the Arabidopsis phyA mutant exposed to blue light/UV-A relative to wild type, thus definitively linking phyA signaling to these photoresponses. To our knowledge, the major role of phyA in mediating the blue light/UV-A photoresponses is a new function for phyA in chloroplast biogenesis at this stage of leaf development. Although rbcL expression in plants exposed to UV-A was 50% less in the phyA mutant relative to wild type, blue light-induced rbcL expression was not significantly affected in the phyA, phyB, and cry1 mutants. However, rbcL expression in blue light was 60% less in the phytochrome chromophore mutant, hy2, relative to wild type, indicating that another phytochrome species (phyC, D, or E) was involved in blue light-induced rbcL transcription. Therefore, at least two different phytochromes, as well as phytochrome-independent photosensory pathways, mediated blue light/UV-A-induced transcription of chloroplast genes in mature leaves.

Protein Disulfide Isomerase-2 of Arabidopsis Mediates Protein Folding and Localizes to Both the Secretory Pathway and Nucleus, Where It Interacts with Maternal Effect Embryo Arrest Factor

“…RNA concentration was determined spectrophotometrically and its integrity was verified using denaturing gel electrophoresis (Chun et al, 2001). For RT-PCR, the RNA was treated with RNase-free DNase (Promega Inc., USA) and used to produce the first-strand cDNA with M-MLV reverse transcriptase (Promega, USA).…”

Tissue- and isoform-specific phytochrome regulation of light-dependent anthocyanin accumulation in Arabidopsis thaliana

“…22 Additionally, phyA has been shown to have a role in regulating photoresponses under B illumination. [23][24][25][26][27][28][29][30] The remaining phytochromes, phyB through phyE, contribute to changes in growth and development, primarily in response to R wavelengths. 19,[31][32][33][34][35][36] Notably, spatially localized…”

Spatial-specific phytochrome responses during de-etiolation in <span style="font-style

“…15,18,[20][21][22] It has been shown that phyA has additional roles under Bc, including activation of chloroplast transcription in mature leaves under B. 23 Furthermore, it was reported recently that phyA has a major role in the early induction of gene expression for GUN4 and CHLH in Bc light. 24 Results from prior studies demonstrated that 35S::pBVR lines exhibit elongated hypocotyls under Bc light.…”