Article

Differential regulation of wheat quinone reductases in response to powdery mildew infection.

Department of Biology, University of Saskatchewan, Saskatoon, SK, S7N 5E2, Canada.
Planta (Impact Factor: 3.38). 12/2005; 222(5):867-75. DOI: 10.1007/s00425-005-0029-7
Source: PubMed

ABSTRACT At least two types of quinone reductases are present in plants: (1) the zeta-crystallin-like quinone reductases (QR1, EC 1.6.5.5) that catalyze the univalent reduction of quinones to semiquinone radicals, and (2) the DT-diaphorase-like quinone reductases (QR2, EC 1.6.99.2) that catalyze the divalent reduction of quinones to hydroquinones. QR2s protect cells from oxidative stress by making the quinones available for conjugation, thereby releasing them from the superoxide-generating one electron redox cycling, catalyzed by QR1s. Two genes, putatively encoding a QR1 and a QR2, respectively, were isolated from an expressed sequence tag collection derived from the epidermis of a diploid wheat Triticum monococcum L. 24 h after inoculation with the powdery mildew fungus Blumeria graminis (DC) EO Speer f. sp. tritici Em. Marchal. Northern analysis and tissue-specific RT-PCR showed that TmQR1 was repressed while TmQR2 was induced in the epidermis during powdery mildew infection. Heterologous expression of TmQR2 in Escherichia coli confirmed that the gene encoded a functional, dicumarol-inhibitable QR2 that could use either NADH or NADPH as an electron donor. The localization of dicumarol-inhibitable QR2 activity around powdery mildew infection sites was accomplished using a histochemical technique, based on tetrazolium dye reduction.

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    ABSTRACT: Quinone reductases (EC 1.5.6.2) are flavoproteins that protect organisms from oxidative stress. The function of plant quinone reductases has not as yet been addressed in vivo despite biochemical evidence for their involvement in redox reactions. Here, using knock-out and over-expressing lines, we studied the protective role of two groups of Arabidopsis thaliana cytosolic quinone reductases, Nqr and Fqr, in response to infection by necrotrophic fungi. The knock-out lines nqr- and fqr1- displayed significantly slower development of lesions of Botrytis cinerea and Sclerotinia sclerotium in comparison to the WT. Consistent with this observation, the over-expressing line FQR1+ was hypersensitive to the pathogens. Both the nqr- and fqr1- displayed increased fluorescence of 2',7'-dichlorofluorescein,‬ a reporter for reactive oxygen species in response to B. cinerea. Infection by B. cinerea was accompanied with increased Nqr and Fqr1 protein levels in the WT as revealed by western blotting. In addition, a marked stimulation of salicylic acid-sensitive transcripts and supression of jasmonate-sensitive transcripts was observed in moderately wounded QR KO mutant leaves, a condition mimicking the early stage of infection. In contrast to the above observations, germination of conidia was accelerated on leaves of QR KO mutants in comparison with the WT and FQR1+ . The same effect was observed in water-soluble leaf surface extracts. It is proposed that the altered interaction between B. cinerea and the quinone reductase mutants is a consequence of subtly altered redox state of the host, which perturbs host gene expression in response to environmental stress such as fungal growth.‬‬‬‬‬‬
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