Reduction of light-induced anthocyanin accumulation in inoculated sorghum mesocotyls. Implications for a compensatory role in the defense response.
Sorghum (Sorghum bicolor L. Moench) accumulates the anthocyanin cyanidin 3-dimalonyl glucoside in etiolated mesocotyls in response to light. Inoculation with the nonpathogenic fungus Cochliobolus heterostrophus drastically reduced the light-induced accumulation of anthocyanin by repressing the transcription of the anthocyanin biosynthesis genes encoding flavanone 3-hydroxylase, dihydroflavonol 4-reductase, and anthocyanidin synthase. In contrast to these repression effects, fungal inoculation resulted in the synthesis of the four known 3-deoxyanthocyanidin phytoalexins and a corresponding activation of genes encoding the key branch-point enzymes in the phenylpropanoid pathway, phenylalanine ammonia-lyase and chalcone synthase. In addition, a gene encoding the pathogenesis-related protein PR-10 was strongly induced in response to inoculation. The accumulation of phytoalexins leveled off by 48 h after inoculation and was accompanied by a more rapid increase in the rate of anthocyanin accumulation. The results suggest that the plant represses less essential metabolic activities such as anthocyanin synthesis as a means of compensating for the immediate biochemical and physiological needs for the defense response.
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Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907-1155, USA.
Nicholson
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D000217:Acyltransferases / Q000235:genetics; D000429:Alcohol Oxidoreductases / Q000235:genetics; D000872:Anthocyanins / Q000032:analysis / Q000096:biosynthesis* / Q000528:radiation effects; D001578:Benzopyrans / Q000378:metabolism; D015152:Blotting, Northern; D002851:Chromatography, High Pressure Liquid; D018548:Cotyledon / Q000235:genetics / Q000382:microbiology / Q000528:radiation effects; D002523:Edible Grain / Q000378:metabolism* / Q000382:microbiology / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant; D005960:Glucosides / Q000235:genetics; D005964:Glucosyltransferases / Q000235:genetics; D008027:Light; D006899:Mixed Function Oxygenases / Q000235:genetics; D008969:Molecular Sequence Data; D010650:Phenylalanine Ammonia-Lyase / Q000235:genetics; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology*; D010936:Plant Extracts / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics; D012717:Sesquiterpenes; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013729:Terpenes; D000094162:Phytoalexins
D000872:Anthocyanins; D001578:Benzopyrans; D005960:Glucosides; D010936:Plant Extracts; D010940:Plant Proteins; D012717:Sesquiterpenes; D013729:Terpenes; C053376:pathogenesis-related proteins, plant; C017154:cyanidin; D006899:Mixed Function Oxygenases; D000429:Alcohol Oxidoreductases; C056570:dihydroflavanol 4-reductase; C048797:flavanone 3-dioxygenase; D000217:Acyltransferases; C020141:flavanone synthetase; D005964:Glucosyltransferases; C023249:flavonol 3-O-glucosyltransferase; D010650:Phenylalanine Ammonia-Lyase; D000094162:Phytoalexins