The brown planthopper (Nilaparvata lugens Stål, BPH) is the most destructive insect pest of rice (Oryza sativa), that can cause leaf wilting and complete drying of whole rice plants. It is a migratory pest and has developed high resistance to pesticide. The increased importance of BPH as a pest has prompted world-wide efforts to identify sources of resistance for breeding resistant varieties. Understanding the molecular mechanism of rice resistance to BPH will help to develop high yield and resistant rice.
We have developed a BPH-resistant rice line derived from a wide-hybridization of wild rice O. officinalis and cultivated rice. Then we isolated the BPH resistance gene Bph14 from the line via the map-based cloning strategy. Bph14 encodes a CC-NB-LRR receptor. BPH14 forms a homocomplex and enhances WRKY transcription factor activity to confer resistance to BPH. During it feeding on rice plant, BPH secretes saliva, which contains different kinds of proteins, into rice cells. Through yeast two-hybrid screening, we identified a BPH salivary protein, BISP, that interacts with BPH14. In the common susceptible rice, BISP interacts with OsRLCK185 and suppresses its phosphorylation activity, thereby inhibiting basal defence and promoting BPH feeding on the rice plant. However, in resistant rice carrying Bph14, BISP binds directly to the LRR domain of BPH14 and triggers strong host plant resistance, which suppresses the insect feeding by occlusion of sieve tube.
We observed that continuous activation of Bph14-mediated immunity negatively impacts plant growth and yield. Rice fine-tunes this resistance through autophagy. Upon BISP-BPH14 complex formation, both proteins interact with the selective autophagy receptor OsNBR1, which recruits OsATG8 to deliver BISP into autophagosomes for degradation. This mechanism fine tunes the resistance and allow us to develop high-yield, insect-resistant varieties to control BPH insect.
We have isolated several BPH resistance genes. Bph14, Bph15, Bph6, Bph9 and Bph30 are widely employed in rice breeding programs. A number of BPH-resistant rice varieties are developed and released to farmers. The results show that the growing of resistant rice varieties has significantly reduced the field density of BPH insects. The promotion of these new varieties has effectively enhanced pest resistance while reducing pesticides and improving yield.
