Constitutively expressed small heat shock protein LsHsp21.5 not only enhances heat tolerance but also helps to maintain reproduction in female Laodelphax striatellus.

Coping with stressful conditions and maintaining reproduction are two key biological processes that affect insect population dynamics. Small heat shock proteins (sHSPs) are involved in the stress response and the development of insects. The sHsp gene Laodelphax striatellus (Hemiptera: Delphacidae) sHsp 21.5 (LsHsp21.5) showed constitutive, stage- and organ-specific expression in L. striatellus, a pest that damages cultivated rice in east Asia. The expression of LsHsp21.5 was highest in the ovary, with 43.60, 12.99 and 1.45 time higher expression here than in the head, gut and female fat bodies, respectively. The expression of this gene was weakly affected by heat or cold shock. The gene provided in vitro protection against heat damage to malate dehydrogenase and in vivo protection against heat stress in Escherichia coli (Enterobacteriales: Enterobacteriaceae) BL21(DE3) and L. striatellus. Moreover, L. striatellus reproduction decreased by 1.85 times when the expression of LsHsp21.5 was inhibited by RNA interference. The expression of some genes related to reproduction, such as the homologous gene of chorion protein, also declined. These results suggest that LsHsp21.5 expression not only protects other proteins against stress but also helps maintain the stable expression of some reproduction-related genes under non-stressful conditions, with impacts on L. striatellus fecundity.

Planthopper-Secreted Salivary Calmodulin Acts as an Effector for Defense Responses in Rice.

The brown planthopper (Nilaparvata lugens, BPH) and small brown planthopper (Laodelphax striatellus, SBPH) are major pests of rice (Oryza sativa) in Asia. These piercing-sucking insects secrete saliva into the host during feeding. Nevertheless, it is largely unknown how planthoppers use salivary effectors to enable continuous feeding on rice. Here, we screened their salivary proteomes and selected eight salivary proteins conserved between SBPH and BPH as candidate effectors. Silencing calmodulin (CaM) impeded BPH and SBPH from penetrating the phloem. Hence, their food intake, survival, and fecundity on rice plants were reduced. By contrast, CaM silencing had a small effect on the survival rate of BPH and SBPH raised on artificial diet. The CaM amino acid sequences were the same for both BPH and SBPH. CaM was highly expressed in their salivary glands and secreted into the rice plants during feeding. Bacterially expressed recombinant CaM protein exhibited calcium-binding activity. In planta expression disclosed that CaM was localized to the plant cytoplasms and nuclei and suppressed plant defenses such as hydrogen peroxide (H2O2) accumulation and callose deposition. CaM-silenced BPH and SBPH nymphs elicited relatively high levels of H2O2 and callose accumulation in rice plants. The foregoing results reveal that CaM is an effector as it enables the planthopper to reach the phloem by suppressing callose deposition and H2O2 accumulation in rice.