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

Abstract

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.

Keywords: Sogatella furcifera; mucin-like protein; plant-insect interaction; rice defense response; salivary proteins.

Figure 1

Relative expression level of SFMLP in WBPH after injection of dsRNA. dsGFP indicates WBPH injected with GFP-dsRNA; dsSFMLP indicates WBPH injected with SFMLP-dsRNA. The mRNA expression level in the dsGFP group is designated as 1.0. ** indicates statistically significant differences (t-test: p < 0.01). Bars, ±SEM.

Figure 2

Effects of SFMLP silencing on WBPH performance. (A) The excreted honeydew of WBPH after injection of dsRNA; (B) the body weight gains of newly emerged WBPH females and males injected with dsRNA. dsGFP indicates WBPH injected with GFP-dsRNA; dsSFMLP indicates WBPH injected with SFMLP-dsRNA. * and ** indicate statistically significant differences (t-test: p < 0.05 and p < 0.01). Bars, ±SEM.

Figure 3

Effects of SFMLP knockdown on the survival rates of WBPH. dsGFP indicates WBPH injected with GFP-dsRNA; dsSFMLP indicates WBPH injected with SFMLP-dsRNA. (A) The survival rates of WBPH feeding on TN1; (B) the survival rates of WBPH feeding on artificial diet. “**” indicates statistically significant differences (t test: p < 0.01). Bars, ±SEM.

Figure 4

Effects of SFMLP knockdown on feeding behaviour of WBPH dsGFP indicates WBPH injected with GFP-dsRNA; dsSFMLP indicates WBPH injected with SFMLP-dsRNA. * and ** indicate statistically significant differences (t-test: p < 0.05 and p < 0.01). Bars, ±SEM.

Figure 5

Effects of SFMLP knockdown on the morphology of the salivary gland of WBPH. (A) WBPH injected with dsGFP; (B) WBPH injected with dsSFMLP. PG indicates the principal gland. The arrow indicates the A-follicle of the principal gland.

Figure 6

Effects of SFMLP knockdown on the morphology of the salivary sheath of WBPH (A) and (B) WBPH injected with dsGFP; (C) WBPH injected with dsSFMLP.

Figure 7

Effects of SFMLP knockdown on the probing trace of WBPH. (A) WBPH injected with dsGFP; (B) WBPH injected with dsSFMLP; (C) enlargement of the probing trace. SS, salivary sheath; SH, stylet hole; SF, salivary flange; (D) the flange number of WBPH injected with dsSFMLP. After feeding on rice for 24 h, the salivary sheaths were collected and observed under SEM. ** indicates statistically significant differences (t-test: p < 0.01). Bars, ±SEM.

Figure 8

Relative expression levels of SFMLP in WBPHs feeding on transgenic plants. (A) SFMLP expression levels of WBPH feeding on SFMLP-dsRNA-transgenic plants (Silence) for 48 h and 64 h. (B) SFMLP expression levels of WBPH feeding on SFMLP-overexpressing transgenic plants (Overexpression) for 48 h and 64 h. * indicates statistically significant differences (t-test: p < 0.05). Bars, ±SEM.

Figure 9

Effects on performance for WBPH feeding on transgenic plants. (A) Honeydew and (B) weight gains of WBPH feeding on SFMLP-dsRNA-transgenic plants (silence). (C) Honeydew and (D) weight gain of WBPH feeding on SFMLP-overexpressing transgenic plants (overexpression). ** indicates statistically significant differences (t-test: p < 0.01). Bars, ±SEM.

Figure 10

Relative expression levels of JA marker and SA marker genes in transgenic rice. (A) The expression levels of four genes in SFMLP-dsRNA-transgenic plants (dsSFMLP) and wild-type plants (WT); (B) the expression levels of four genes in SFMLP-overexpressing transgenic plants (SFMLP) and WT plants. * and ** indicate statistically significant differences (t-test: p < 0.05 and p < 0.01). Bars, ±SEM.

Figure 11

Relative expression levels of JA marker and SA marker genes in rice plants infested by WBPH. (A) The expression levels of genes in the WT plants and WT plants infested by WBPH (WT-infested); (B) the expression levels of genes in the SFMLP-dsRNA-transgenic plants (dsSFMLP) and dsSFMLP plants infested by WBPH (SFMLP-infested); (C) the expression levels of genes in the SFMLP-overexpressing-transgenic plants (SFMLP) and SFMLP plants infested by WBPH (SFMLP-infested). * and ** indicate statistically significant differences (t-test: p < 0.05 and p < 0.01). Bars, ±SEM.