Sogatella furcifera Saliva Mucin-like Protein Is Required for Feeding and Induces Rice Defences.

The white-backed planthopper (WBPH), Sogatella furcifera, is one of the most important piercing-sucking pests of rice (Oryza sativa) in Asia. Mucin-like salivary protein (SFMLP) is highly expressed in the salivary glands of WBPH, which plays an important role in WBPH feeding. In this study, WBPH injected with dsSFMLP had difficulty in sucking phloem sap from rice plants, which significantly reduced their food intake, weight, and survival. In contrast, the knockdown of the SFMLP gene had only a marginal effect on the survival of WBPH fed an artificial diet. Further studies showed that silencing SFMLP resulted in the short and single-branched salivary sheaths secretion and less formation of salivary flanges in rice. These data suggest that SFMLP is involved in the formation of the salivary sheath and is essential for feeding in WBPH. Overexpression of the SFMLP gene in rice plants promoted the feeding of WBPH, whereas silencing the gene in rice plants significantly decreased WBPH performance. Additionally, it was found that overexpression of SFMLP in rice plants elicited the signalling pathway of SA (salicylic acid) while suppressing JA (jasmonic acid); in contrast, silencing of the SFMLP gene in rice plants showed the opposite results. This study clarified the function of SFMLP in WBPH feeding as well as mediating rice defences.

Transcriptomic and Expression Analysis of the Salivary Glands in Brown Planthoppers, Nilaparvata lugens (Hemiptera: Delphacidae).

The brown planthopper (BPH), Nilaparvata lugens Stål (Hemiptera: Delphacidae), is a serious rice pest because of its destructive feeding. The salivary glands of the BPH play a key role in successful feeding. In this study, we explored the salivary gland transcriptome (sialotranscriptome) of adult BPHs using Illumina sequencing and a total of 55,913 transcripts and 45,421 unigenes were obtained. We identified one reference gene RPL9 (Ribosomal protein L9) and 19 salivary protein genes from the BPH sialotranscripome, which were categorized as those involved in sugar metabolism, extra-oral digestion of cell wall components, detoxification, and suppression of plant defenses. Tissue expression profiles of 19 salivary protein genes analysis revealed that the expression level of alpha-glucosidase family 31 had no difference in five tissues, suggesting that it may have functions in the whole-body parts. Glucose dehydrogenase (flavine adenine dinucleotide, quinone)-like was expressed highly in the salivary gland, which might play putative role in insect feeding. Glucose dehydrogenase (acceptor) was expressed the highest level in head without salivary gland. Other salivary protein genes were highly expressed in gut or malpighian tubule, suggesting that they may play roles in digestive and detoxification mechanism. Moreover, we detected RPL9 is one of the genes that is most consistently present for acquisition of gene expression in different tissues. Thus, RPL9 can be a new reference for expression studies of BPH. The obtained BPH sialotranscripome provides a list of genes that have potential roles in feeding and interaction between BPHs and rice plants.

Proteomic analysis of watery saliva secreted by white-backed planthopper, Sogatella furcifera.

The white-backed planthopper, Sogatella furcifera, is a phloem sap feeder that secretes watery and gelling saliva during feeding. In this study, we identified the major proteins in watery saliva of S. furcifera by shotgun LC-MS/MS analysis combined with transcriptomic analysis. A total of 161 proteins were identified, which were divided into 8 function categories, including enzymes, transporter, calcium ion binding protein, salivary sheath protein, cytoskeleton protein, DNA-, RNA-, and protein-binding or regulating proteins, other non-enzyme proteins and unknown proteins. Gene expression pattern of 11 secretory proteins were analyzed by real time quantitative-PCR. We detected the mucin-like protein, which had a unique expression level in salivary gland, most likely to be a candidate effector involved in regulation of plant defense. This study identified the watery saliva component of S. furcifera and it provided a list of proteins which may play a role in interaction between S. furcifera and rice.