Phytochrome Control of Levels of mRNA Complementar...
Abstract
The involvement of phytochrome in the control of the levels of RNA transcribed from maize plastid and nuclear genes was examined.The effects of illumination with red light，farred light，or red light followed by farred light on relative amounts of RNAs complementary to maize plastid genes for the large subunit of ribulose bisphosphate carboxylase（RuBPCase）；the 32-kDa thylakoid membrane triazine herbicide binding B protein of photosystem Ⅱ；the a，β and ∈ subunits of CF1；subunit Ⅲ（protontranslocating）of CF0；the reaction center proteins Al and A2 of photosystem I；two other light-induced genes for membrane proteins of photosystem Ⅱ（ORFs 353 and 473）；and one gene for an unidentified membrane protein（UORF 443）were measured by hybridization of labeled DNA probes to samples of leaf RNA.Transcripts of two nuclear-encoded genes，the genes for the small subunit of RuBPCase and the light-harvesting chlorophyll a/b binding protein，were studied in the same way.The levels of RNA complementary to all of these light induced genes were significantly increased within 3 to 6 hours after brief illumination with red light.The stimulatory effects of red light were largely reversed by subsequent illumination with farred light.It is concluded that phytochrome controls increases in the levels of mRNAs complementary to certain plastid and nuclear genes in dark-grown maize seedlings.
①Yu S.Zhu，Present address：Deparlment of Microbiology，University of Illinois at Urbana-Champaign，Urbana，IL 61801.
② Shain D.Kung，Permanent address：Department of Biological Sciences，University of Maryland Baltimore County，Catonsville，MD 21228.
③ Lawrence Bogorad
Department of Cellular and Developmemal Biology，The Biological Laboratories，Harvard University，Cambridge，Massachusetts 02138(https://www.daowen.com)
Various segments of this research were supported in part by research grants from the National Science Foundation，the Competitive Research Grants Office of the United States Department of Agriculture，and the National Institute of General Medical Sciences（L.B.）.It was also aided by the Maria Moors Cabot Foundation for Botanical Research of Harvard University.
During light-induced development of etioplasts into chloroplasts，morphological，structural and biochemical changes occur，including the accumulation of Chl，the formation of thylakoid membrane proteins and lipids，increases in levels of some enzymes，an increase in chloroplast RNA polymerase activity，and increases in various RNA species［1，5，6，10，14，17，25，28］.The first major plastid DNA sequence whose transcript level was shown to increase during greening was photogene 32，the gene for a 32-kDa thylakoid membrane polypeptide in maize［3，17］.This polypeptide has been shown to bind triazine herbicides and appears to be the B protein of PSII；thus，the gene is designated ps2B［23］.（It has also been designated psbA［18］.）Photo-regulation of ps2B transcription has also been reported in other plants［12，20，28］.Recently，a number of other photoregulated genes have been mapped on the maize chloroplast chromosome and characterized in this laboratory（Castroveijo K M T，Muskavitch E T，Krebbers H，Roy D R，Russell L，Bogorad，unpublished data）［8，25］.These include，in addition to ps2B：rcL—encoding the large subunit of ribulose biphosphate carboxylase［19］；cf1 A B and E—encoding the α，β，and ∈ subunits，respectively of CF14（Rodermel S，Bogorad L，unpublished data）the coupling factor 1 for photosynthetic phosphorylation［25］；cfoⅢ-encoding subunit Ⅲ of CF0［25］；pslA1 and ps1A2—encoding polypeptides of P700—the reaction center of PSI［13，25］；ORFs 473，353—encoding PSⅡproteins of 473 and 353 amino acids，respectively-and UORF 443-encoding an unidentified membrane polypeptide（Krebbers E T，Muskavitch K M，Orr E A，Schantz R，Castroveijo M and Bogorad L，unpublished data）.In addition，expression of nuclear genes rcS（encoding the small subunit of ribulose biphosphate carboxylase）and/or cab（encoding the light harvesting Chl a/b binding protein）have been demonstrated to be induced by light in barley，Lemna，pea，bean，and maize［2，16，25，28，29］.For convenience，the term‘photogene’is used to designate a gene whose transcript level increases significantly during light-induced development.
The major photomorphogenic system of plants is driven by the R and FR reversible phytochrome receptor［11，21，22，27］.In some cases，a blue light receptor may be involved in photomorphogenesis［21，24］.Phytochrome is a bile pigment-protein complex that has two photointerconvertible forms：Pr and Pfr with absorption maxima at 660 and 730 nm，respectively［11］.Photoconversion of Pr to Pfr by R potentiates a diverse array of morphogenic responses that are not exhibited if the Pfr is promptly reconverted to Pr by illumination with FR.
To understand the molecular mechanisms that govern light-dependent changes during greening，it is necessary to identify the photoreceptor（or photoreceptors）that regulate expression of maize photogenes.It has been shown by others［2，16，20，26，28，29］that RNA levels of rcS，cab，ps2B，and rcL are affected by phytochrome in at least one plant species.The results presented here demonstrate that the levels of RNAs complementary to these and several other sets of photoregulated plastid and nuclear genes of maize are controlled by phytochrome.
