Application of Brown Planthopper Salivary Gland Extract to Rice Plants Induces Systemic Host mRNA Patterns Associated with Nutrient Remobilization

Insect saliva plays an important role in modulation of plant-insect interactions. Although this area of research has generated much attention in recent years, mechanisms of how saliva affects plant responses remain poorly understood. To address this void, the present study investigated the impact of the brown planthopper (Nilaparvata lugens, Stål; hereafter BPH) salivary gland extract (SGE) on rice (Oryza sativa) systemic responses at the mRNA level. Differentially expressed rice mRNAs were generated through suppression subtractive hybridization (SSH) and classified into six functional groups. Those with the most representatives were from the primary metabolism (28%), signaling-defense (22%) and transcription-translation-regulation group (16%). To validate SSH library results, six genes were further analyzed by One-Step Real-Time Reverse Transcriptase-PCR. Five of these genes exhibited up-regulation levels of more than 150% of those in the control group in at least one post-application time point. Results of this study allow assignment of at least two putative roles of BPH saliva: First, application of SGE induces immediate systemic responses at the mRNA level, suggesting that altering of the rice transcriptome at sites distant to hoppers feeding locations may play an important role in BPH-rice interactions. Second, 58% of SGE-responsive up-regulated genes have a secondary function associated with senescence, a process characterized by remobilization of nutrients. This suggests that BPH salivary secretions may reprogram the rice transcriptome for nutritional enhancement. When these findings are translated onto ‘whole plant’ scale, they indicate that BPH saliva may play the ‘wise investment’ role of ‘minimum input today, maximum output tomorrow’.