An Arabidopsis Mutant Hypersensitive to Red and Far-Red Light Signals

Abstract

A new mutant called psi2 (for p hytochrome si gnaling) was isolated by screening for elevated activity of a chlorophyll a / b binding protein-luciferase ( CAB2-LUC ) transgene in Arabidopsis. This mutant exhibited hypersensitive induction of CAB1 , CAB2 , and the small subunit of ribulose-1,5-bisphosphate carboxylase ( RBCS ) promoters in the very low fluence range of red light and a hypersensitive response in hypocotyl growth in continuous red light of higher fluences. In addition, at high-but not low-light fluence rates, the mutant showed light-dependent superinduction of the pathogenrelated protein gene PR-1a and developed spontaneous necrotic lesions in the absence of any pathogen. Expression of genes responding to various hormone and environmental stress pathways in the mutant was not significantly different from that of the wild type. Analysis of double mutants demonstrated that the effects of the psi2 mutation are dependent on both phytochromes phyA and phyB. The mutation is recessive and maps to the bottom of chromosome 5. Together, our results suggest that PSI2 specifically and negatively regulates both phyA and phyB phototransduction pathways. The induction of cell death by deregulated signaling pathways observed in psi2 is reminiscent of retinal degenerative diseases in animals and humans. INTRODUCTIONBecause light provides the energy source for photosynthesis, plants must adapt to changes in ambient light quantity and quality to optimize the efficiency of this important process. The results of this adaptation are apparent: almost every step of plant development, from seed germination to fruit maturation, is dependent on light. Moreover, light regulates the circadian rhythm, the adaptative size modification of tissue and organs, and the expression of photosynthetic genes and many other known and unknown genes (Terzaghi and Cashmore, 1995).To date, what we know about light information processing and signal transduction concerns the nature and function of photoreceptors. A family of photoreceptors called phytochromes has been shown to be involved in the perception of red and far-red light. Their biochemical and molecular properties and physiological roles are now well described (reviewed in Quail et al., 1995;Smith, 1995). In addition, a longpostulated UV and blue light receptor (cryptochrome) was recently characterized by Ahmad and Cashmore (1993). Mutants lacking one or several of these receptors have provided useful information concerning the role of individual photoreceptors and their interaction in transducing light signals (reviewed in Barnes et al., 1997).Much less is known concerning molecules that link light perception to gene activation. The CONSTITUTIVE PHOTO-MORPHOGENIC/DEETIOLATED/FUSCA (COP/DET/FUS) class of proteins has been suggested to play an important role in regulating the repression of light-inducible genes and the maintenance of skotomorphogenesis (Chory et al., 1989). For some of these proteins, the genes have been cloned and include COP1 (Deng et al., 1992), DET1 (Pepper et al., ...

The Protein Phosphatase 7 Regulates Phytochrome Signaling in Arabidopsis

“…In this double mutant, a clear reversion of the phenotypic reduction of cell elongation in the psi2-DS1 mutant was observed in continuous white light (Figure 4A), as well as in continuous low red light (Figure 4B), a discriminating condition for the involvement of both phyA and phyB in the psi2 phenotype [26]. This reversion notably affected both the expression of the PR1 gene after treatment with 250 µM SA (Figure 4C) and the formation of HR at high light (data not shown).…”

“…The psi2 mutant contains wild type levels of these phytochromes and shows an apparently unaltered sensitivity to blue light [26]. We have now isolated and identified the wild type gene corresponding to psi2 and studied how the related protein regulates the levels of phyA and phyB signals.…”

Seduced by the dark side: integrating molecular and ecological perspectives on the influence of light on plant defence against pests and pathogens

“…First is the observation that lesion formation in many of these mutants is light‐dependent (e.g. Johal et al ., 1995; Genoud et al ., 1998; Brodersen et al ., 2002). Secondly, cloning of several of the genes defined by these mutations has identified a number of genes involved in chlorophyll biosynthesis or degradation (e.g.…”

“…Evidence for this type of regulation has been recently uncovered in Arabidopsis. Genoud et al . (1998) identified an Arabidopsis light signalling mutant, psi2 (phytochrome signalling), which, in addition to effects on light‐dependent expression of photosynthetic genes, displayed light‐dependent development of spontaneous necrotic lesions and increased PR1 gene expression.…”

Circadian control of abscisic acid biosynthesis and signalling pathways revealed by genome‐wide analysis of LHY binding targets

“…The oscillatory mechanism of the clock is based on a transcriptional–translational feedback loop composed of three inhibitory steps (Pokhilko et al ., ; Carré & Veflingstad, ). The LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED‐1 (CCA1) transcription factors are expressed in the early morning (Genoud et al ., ; Wang & Tobin, ) and bind to Evening Element (EE) motifs (AAAATATCT) in the promoters of PSEUDO ‐ RESPONSE REGULATOR 9 , 7 and 5 ( PRR9 , ‐ 7 and ‐ 5 ) and of PRR1 , also known as TIMING OF CAB2 EXPRESSION1 ( TOC1 ; Harmer et al ., ; Matsushika et al ., ; Strayer et al ., ; Alabadi et al ., ; Adams et al ., ). As LHY and CCA1 protein levels decline in the afternoon, the PRR proteins are expressed in successive waves and act to repress LHY and CCA1 transcription until the following morning (Nakamichi et al ., ).…”