Leafhopper salivary carboxylesterase suppresses JA-Ile synthesis to facilitate initial arbovirus transmission in rice phloem

Abstract

Plant jasmonoyl-L-isoleucine (JA-Ile) is a major defense signal against insect feeding, but whether or how insect salivary effectors suppress JA-Ile synthesis and thus facilitate viral transmission in plant phloem remains elusive. Insect carboxylesterases (CarEs) are the third major family of detoxification enzymes. Here, we identify a new leafhopper CarE10 that specifically expressed in salivary glands and is secreted into rice phloem as the saliva component. Leafhopper CarE10 directly binds and promotes rice Jasmonate resistant 1 (JAR1) degradation by the proteasome system. Moreover, the direct association of CarE10 with JAR1 obviously impairs JAR1 enzyme activity for JA conversion to JA-Ile in in-vitro JA-Ile synthesis system. A devastating rice reovirus activates and promotes co-secretion of virions and CarE10 by virus-induced vesicles into saliva-stored salivary cavities of leafhopper vectors and ultimately into rice phloem to establish initial infection. Furthermore, virus-mediated increase of CarE10 secretion or overexpression of CarE10 in transgenic rice plants causes the reduced levels of JAR1 and thus suppresses JA-Ile synthesis, thereby promoting host attractiveness to insect vectors and facilitating initial viral transmission. Our findings provide insights into how insect salivary protein CarE10 suppresses host JA-Ile synthesis to benefit initial virus transmission in rice phloem.