Kleine T, Kindgren P, Benedict C, Hendrickson L, Strand Å
Genome-wide gene expression analysis reveals a critical role for CRYPTOCHROME1 in response of Arabidopsis to high irradiance
Plant Physiology: 2007 144:1391-1406

Exposure to high irradiance results in dramatic changes in nucleargene expression in plants. However, little is known about themechanisms by which changes in irradiance are sensed and howthe information is transduced to the nucleus to initiate thegenetic response. To investigate whether the photoreceptorsare involved in the response to high irradiance, we analyzedexpression of EARLY LIGHT-INDUCIBLE PROTEIN1 (ELIP1), ELIP2,ASCORBATE PEROXIDASE2 (APX2), and LIGHT-HARVESTING CHLOROPHYLLA/B-BINDING PROTEIN2.4 (LHCB2.4) in the phytochrome A (phyA),phyB, cryptochrome1 (cry1), and cry2 photoreceptor mutants andlong hypocotyl5 (hy5) and HY5 homolog (hyh) transcription factormutants. Following exposure to high intensity white light for3 h (1,000 µmol quanta m–2 s–1) expressionof ELIP1/2 and APX2 was strongly induced and LHCB2.4 expressionrepressed in wild type. The cry1 and hy5 mutants showed specificmisregulation of ELIP1/2, and we show that the induction ofELIP1/2 expression is mediated via CRY1 in a blue light intensity-dependentmanner. Furthermore, using the Affymetrix Arabidopsis (Arabidopsisthaliana) 24 K Gene-Chip, we showed that 77 of the high light-responsivegenes are regulated via CRY1, and 26 of those genes were alsoHY5 dependent. As a consequence of the misregulation of thesegenes, the cry1 mutant displayed a high irradiance-sensitivephenotype with significant photoinactivation of photosystemII, indicated by reduced maximal fluorescence ratio. Thus, wedescribe a novel function of CRY1 in mediating plant responsesto high irradiances that is essential to the induction of photoprotectivemechanisms. This indicates that high irradiance can be sensedin a chloroplast-independent manner by a cytosolic/nucleic component.

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