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Abstract
Hydroxyproline-rich glycoproteins (HRGPs) accumulation and oxidative cross-linking is one of the earliest defense responses in plants against pathogen infection. In the present study HRGP accumulation in three sorghum genotypes i.e. SC146 (resistant), cv. SC326 (intermediately resistant) and BTx623 (susceptible) as a response to Colletotrichum sublineolum isolate CP2126 infection is elucidated. HRGPs were monitored by hydroxyproline (Hyp) estimation. In genotypes SC146 and genotypes SC326 there was a significantly higher amounts of Hyp at 2 days after inoculation (dai) compared to genotype BTx623, indicating an infection induced accumulation of HRGPs. Western blot analysis of acid-ethanol extracted proteins with polyclonal antibody raised against pearl millet purified HRGPs identified four bands with molecular masses of ~65, 45, 17 and 14 kDa as HRGPs. Insolubilization of the 45 kDa protein in genotypes SC146 and SC326 upon infection with C. sublineolum indicates a role of this protein in cell wall cross-linking, coinciding with heavier accumulation of hydrogen peroxide. In addition, tissue print analysis using polyclonal antibody of pearl millet HRGPs recognized these cross-linked proteins to be HRGPs. These findings indicated that HRGPs in sorghum is a component of defense reaction against C. sublineolum infection.
Acknowledgements
We thank the Danish International Development Assistance (DANIDA) for financial support. This work was supported by a grant for Enhancement of Research Capacity (ENRECA), i.e., ‘Systemic Acquired Resistance – an eco-friendly strategy for managing diseases in rice and pearl millet’. The authors thank Professor V. Raggi, Università di Perugia, Italy, for his valuable comments and suggestions during the preparation of the manuscript. The authors thank K. Reilly for cMeHRGP1 cDNA probe. SS acknowledges the research fellowship received from Council of Scientific and Industrial Research, New Delhi, India.