Mapping of bacterial blight resistance gene xa8 in rice (Oryza sativa L.)

Abstract

Bacterial blight (BB) of rice, caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the major diseases causing yield losses in rice worldwide. Development and deployment of resistant rice cultivars and pyramiding two or more resistance genes into elite varieties is the only strategy available to combat the disease. The BB resistance gene, xa8 conferred complete resistance to only one pathotype and partial resistance against two pathotypes at seedling stage while complete resistance against five of the seven pathotypes prevalent in Punjab at adult plant stage. The gene was earlier mapped on rice chromosome 7 at 19.9 cM genetic distance from SSR marker, RM214 using a recombinant inbred line (RIL) population generated from the cross between PR106 and IRBB8. However, due to the paucity of markers in that region, the gap could not be narrowed.With the availability of new SSR markers in that region, the gene was placed between two consecutive SSR markers, RM21044 and RM21045 at 7.0 and 9.9 cM respectively. Analysis of the 9.5 kb DNA sequence harboring the xa8 gene revealed the presence of three intact genes, which codes for putative expressed proteins viz., Zinc finger A20 and AN1 domain-containing protein (LOC_Os07g07400), Oxidoreductase, 2OG-Fe oxygenase family protein (LOC_Os07g07410) and Gibberellin 20 oxidase 1-B protein (LOC_Os07g07420). All the three genes are involved in plant response to various stresses and could be the possible candidate genes for xa8.