Rapid intracellular acidification is a novel plant defense response countered by the brown planthopper

SUMMARY The brown planthopper (BPH) is the most destructive insect pest in rice. Through a stylet, BPH secrets a plethora of salivary proteins into rice phloem cells as a crucial step of infestation. However, how various salivary proteins function in rice cells to promote insect infestation is poorly understood. Among them, one of the salivary proteins is predicted to be a carbonic anhydrase (NlCA). The survival rate of the NlCA- RNA interference (RNAi) BPH insects was extremely low on rice, indicating a vital role of this salivary protein in BPH infestation. We generated NICA transgenic rice plants and found that NlCA expressed in rice plants could restore the ability of NlCA- RNAi BPH to survive on rice. Next, we produced rice plants expressing the ratiometric pH sensor pHusion and found that NlCA- RNAi BPH induced rapid intracellular acidification of rice cells during feeding. Further analysis revealed that both NlCA- RNAi BPH feeding and artificial of lowering intracellular pH activated plant defense responses, and that NICA-mediated intracellular pH stabilization is linked to diminished defense responses, including reduced callose deposition at the phloem sieve plates and suppressed defense gene expression. Given the importance of pH homeostasis across the kingdoms of life, discovery of NICA-mediated intracellular pH modulation uncovered a new dimension in the interaction between plants and piecing/sucking insect pests. The crucial role of NICA for BPH infestation of rice suggests that NICA is a promising target for chemical or trans-kingdom RNAi-based inactivation for BPH control strategies in plants. Highlights Rapid intracellular acidification is a novel plant defense response. Brown planthopper delivers into rice tissues a major virulence protein, carbonic anhydrase ( Nl CA), critical for survival. NlCA counters intracellular acidification to suppress plant defense. Results implicate existence of pH-responsive regulators of defense responses in the rice-brown planthopper interaction. In brief The brown planthopper (BPH) is the most devasting insect pest in rice. Jiang et al . discovered that BPH secretes a salivary carbonic anhydrase ( NI CA) to regulate the intracellular pH of the rice cell to facilitate its feeding and survival on rice plants and that NICA-counters host intracellular pH acidification to diminished defense responses. These findings uncovered that intracellular pH homeostasis is a previously uncharacterized battleground in plant-insect interactions, but also open a door to future discovery of pH-responsive intracellular regulators of defense responses, which could add a new research dimension in the study of plant-biotic interactions.