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Title:   Author  item
                                            ADHIKARI, TIKA - N. DAKOTA STATE UNIV.item
                                            BALAJI, BOOVARAGHAN - UNIV. OF MISSOURIitem
                                            BREEDEN, JILL - PURDUE UNIV.item
                                            Goodwin, Stephen

                                                         - *Steve*
  Submitted to: Physiological and Molecular Plant Pathology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/19/2007
                                    Publication  Date: 10/19/2007
                                    Citation: Adhikari, T.B., Balaji, B., Breeden, J., Goodwin, S.B. 2007. Resistance of wheat to Mycosphaerella graminicola involves early and late peaks of gene expression. Physiological and Molecular Plant Pathology. 71:55-68.Interpretive Summary: Septoria tritici blotch (STB), caused by the fungus Mycosphaerella graminicola, is one of the most common and destructive diseases of wheat worldwide. More than 12 resistance genes occur, but almost nothing is known about the mechanisms of resistance or the timing of gene expression in response to the pathogen. To test for differences between resistant and susceptible plants, expression of 14 genes previously associated with the resistance response in wheat was measured from 0 to 27 days after inoculation (DAI) in two resistant and two susceptible cultivars. Four genes only showed an early response to the pathogen from about 3 hours to 1 DAI in the two resistant lines but were not expressed at later time points. Nine other genes had bimodal patterns with both early and late peaks of expression in at least one of the resistant cultivars, but low if any expression in the two susceptible cultivars. The final gene had a trimodal pattern of expression in one resistant cultivar only. This work showed that the resistance response of wheat to M. graminicola is not completed during the first 24 hours after contact with the pathogen, but instead can extend into the period from 18 to 24 DAI when fungal growth increases dramatically in susceptible plants. Expression of one gene at 12 hours after inoculation was much higher in resistant compared to susceptible wheat lines, so could provide a fast method for separating resistant from susceptible lines in breeding programs. This information will be useful to molecular biologists to understand the genetic basis of host-pathogen interactions between wheat and this fungus, to plant pathologists trying to devise better methods of disease control, and to plant breeders to develop new cultivars with improved resistance to STB.
                                Technical Abstract: Expression of 14 genes associated with the resistance response of wheat to the Septoria tritici blotch fungus, Mycosphaerella graminicola, was measured from 0 to 27 days after inoculation (DAI) in two resistant and two susceptible cultivars by real-time quantitative PCR. The four genes chitinase, phenylalanine ammonia lyase, pathogenesis-related protein PR-1, and peroxidase were induced from about 10 to 60 fold at early stages (3 h-1 DAI) during the incompatible interactions but were not expressed at later time points. Nine other genes (ATPase, brassinosteroid-6-oxidase, peptidylprolyl isomerase, peroxidase, 40S ribosomal protein, ADP-glucose pyrophosphorylase, putative protease inhibitor, methionine sulfoxide reductase, and an RNase S-like protein precursor) had bimodal patterns with both early and late peaks of expression in at least one of the resistant cultivars, but low if any induction in the two susceptible cultivars. A serine carboxypeptidase had a trimodal pattern of expression in the resistant cultivar Tadinia. The resistance response of wheat to M. graminicola is not completed during the first 24 hours after contact with the pathogen, but instead can extend into the period from 18 to 24 DAI when fungal growth increases dramatically in compatible interactions. Expression of the PR-1 gene at 12 hours after inoculation was much higher in resistant compared to susceptible recombinant–inbred lines (RILs) segregating for resistance, so could provide a faster method for separating resistant from susceptible lines in plant breeding programs. Significant differential expression in the resistant and susceptible wheat cultivars and RILs after inoculation with M. graminicola suggests that these genes may play a major role in the resistance mechanisms of wheat.


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