UNDERSTANDING THE MOLECULAR MECHANISM OF PROGRAMMED CELL DEATH AND ITS RELATIONSHIP WITH DISEASE RESISTANCE IN RICE

¹ Department of Plant Pathology, The Ohio State University, Kottman Hall, 2021 Coffey Road, Columbus, Ohio 43210-1087, USA

² Institute of Molecular Agrobiology, The National University of Singapore, 1 Research Link, Singapore 117604, Republic of Singapore

³ Singapore Polytechnic, 500 Dover Road, Singapore 139651, Republic of Singapore

⁴ International Rice Research Institute, PO Box 3127, Makati City, Philippines

One of the most common features in host and pathogen interaction is the localized death of the host cells at the infection site, known as hypersensitive response (HR). The HR is correlated with a transient burst of active oxygen species, activation of specific defense-related genes, accumulation of antimicrobial compounds and alterations of the plant cell wall. HR appears to be so intimately involved in resistance that considerable efforts have been made to identify the events that trigger this response, and to define the steps culminating in cell death. We investigated the relationship between spontaneous cell death and disease resistance using nine rice lesion mimic mutants. Trypan blue staining revealed that the lesion mimics which appeared on the leaves of these mutants were due to cell death. Activation of six defense-related genes was observed in most of the mutants when the lesions developed. Three mutants exhibited significant enhanced resistance to rice blast. One of the mutants, spl11, confers non-race specific resistance not only to blast but also to bacterial blight. The level of resistance in spl11 mutant to the two pathogens correlates with the defense-related gene expression and lesion development on the leaves. The results suggest that lesion mimic mutations in rice may provide a clue to developing broad-spectrum resistance to unrelated pathogens. To isolate the gene using a map-based cloning strategy, three RAPD markers tightly-linked to spl11 were identified and mapped onto the rice chromosome 12. High-resolution map at the spl11 locus will be presented.