Phytochrome A mediates blue light and UV-A-dependent chloroplast gene transcription in green leaves.
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.
Chun
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Department of Molecular Biosciences and Biosystems Engineering, University of Hawaii, 1955 East-West Road, AgSciences III, Room 218, Honolulu, Hawaii 96822, USA.
Kawakami
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A
Christopher
D A
DA
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D018548:Cotyledon / Q000378:metabolism / Q000528:radiation effects; D003624:Darkness; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D008027:Light; D010834:Phytochrome / Q000378:metabolism*; D051942:Phytochrome A; D018515:Plant Leaves / Q000378:metabolism* / Q000528:radiation effects; D010947:Plants, Toxic; D011401:Promoter Regions, Genetic / Q000528:radiation effects; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D014158:Transcription, Genetic / Q000528:radiation effects*; D014466:Ultraviolet Rays
D029681:Arabidopsis Proteins; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; D010834:Phytochrome