Rice brown spot resistance gene bsr1 also confers resistance to bacterial blight by suppressing sucrose efflux

Brown spot (BS), caused by the fungal pathogen Bipolaris oryzae , is a major disease threatening global rice production. However, the genetic basis of host BS resistance remains unclear. Here, we identified brown spot resistance 1 ( bsr1 ), a quantitative trait locus conferring BS resistance, by map-based cloning. We show that bsr1 encodes a sucrose transporter and that a near-isogenic line carrying bsr1 ( bsr1 -NIL) in the susceptible Koshihikari genetic background exhibited resistance to BS by suppressing sucrose efflux into the apoplast after pathogen attack. Furthermore, bsr1 -NIL also showed strain-specific resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae through the same mechanism. These findings demonstrate that bsr1 confers dual resistance to fungal and bacterial diseases by regulating sucrose efflux. Our study identifies a previously unrecognized mechanism underlying resistance to both BS and bacterial blight and highlights bsr1 as a promising target for breeding disease-resistance rice cultivars. Rice ( Oryza sativa L.) is a staple food for more than half of the world’s population ¹ . Brown spot (BS), caused by the fungus Bipolaris oryzae , is one of the most prevalent fungal diseases of rice, and its incidence has increased under global warming ² . BS infects coleoptiles, leaves, leaf sheaths, panicle branches, glumes, and spikelets, and severe infection can substantially reduce grain yield.