Plant & Animal Genomes XIV Conference

January 14-18, 2006
Town & Country Convention Center
San Diego, CA

Suppression Of Basal Defense Influences The Timing Of Mla-Mediated Response To Barley Powdery Mildew

Rico A. Caldo¹ , Dan Nettleton² , Jiqing Peng³ , Roger P. Wise^1,4

¹  Department of Plant Pathology and Center for Plant Responses to Environmental Stresses, Iowa State University, Ames, Iowa, 50011-1020, USA

²  Department of Statistics, Iowa State University, Ames, Iowa, 50011-1120, USA

³  Gene Chip Facility, Office of Biotechnology, Iowa State University, Ames, Iowa 50011-3260, USA

⁴  Corn Insects and Crop Genetic Research, USDA-ARS, Iowa State University, Ames, Iowa, 50011-1020, USA

Basal defense is part of all plant-pathogen interactions, yet little is known about its influence on the onset of gene-specific resistance. We performed a meta-analysis of GeneChip mRNA expression for 155 basal defense-related genes of barley (Hordeum vulgare) challenged with Blumeria graminis f. sp. hordei (Bgh) in order to determine how these genes influence responses of plants containing fast and delayed-acting Mla alleles. Transcript accumulation of these genes at early stages of infection was found to be independent of specific Mla powdery mildew resistance alleles, or of the Rar1 co-chaperone, indicating their involvement in non-specific pathogen recognition by the host. In plants undergoing rapid resistance conferred by Mla1, Mla6 or Mla13, transcripts hyper-accumulated from 0 to 16 hai. By contrast, in plants undergoing delayed resistance controlled by Mla12, an early hyper-induction of transcripts from 0 to 8 hai was observed but the expression of many of these genes is markedly suppressed from 8 to 16 hai. Thus, similar to mammalian immunity wherein an innate mechanism influences the expression of the acquired immune response, modulation of basal defense at the early stages of infection may precondition barley epidermal cells to become accessible to the pathogen, thus, impacting the fundamental mechanisms of Mla-specified rapid and delayed resistance to powdery mildew. Research supported in part by USDA-IFAFS grant no. 2001-52100-11346.