Role of H⁺-ATPase in pearl millet downy mildew disease resistance

Abstract

Downy mildew disease is a major devastating disease caused by Sclerospora graminicola in pearl millet. Although disease management studies have indicated several biological as well as chemical control measures, the durability of resistance appears to be a major problem and has been attributed to the lack of understanding of pathogenic or resistance processes at molecular levels. Present study reveals the involvement of plasma membrane H⁺-ATPase in downy mildew disease resistance and offer H⁺-ATPase assay as a tool to evaluate downy mildew disease resistance in host cultivars resistant to all existing pathotypes, pathotypes 1-5. H⁺-ATPase was activated by fungal attack in all resistant cultivars but not in susceptible cultivars. The level of H⁺-ATPase was correlated with the degree of resistance as evaluated by field screening studies. Upregulation of H⁺-ATPase was specifically in the coleoptile region, which is the susceptible site for the attack by the downy mildew pathogen. The upregulated levels of H⁺-ATPase activity were also observed in resistant cell suspension and correlated with acidification of the extracellular medium. There was no change in either H⁺-ATPase activity or acidification in susceptible cell suspensions. Serological evidence for the upregulation of H⁺-ATPase activity only in resistant pearl millet has also been provided using a monoclonal antibody (MAb 46E5B11F6) against maize H⁺-ATPase by ELISA as well as immunoblot. A 100-kDa band was specifically increased 3-fold in the resistant cultivar. The results of the investigation suggest that plasma membrane H⁺-ATPase activity may be involved in the initial step of resistance to the downy mildew disease pathogen and the increase in activity could be due to activation by post translational modification as well as by upregulating the enzyme synthesis.