Abstract
Mitogen-activated protein kinases (MPKs) play a central role not only in plant growth and development, but also in plant responses to abiotic and biotic stresses, including pathogens. Yet, their role in herbivore-induced plant defenses and their underlying mechanisms remain largely unknown. Here, we cloned a rice MPK gene, OsMPK4, whose expression was induced by mechanical wounding, infestation of the striped stem borer (SSB) Chilo suppressalis, and treatment with jasmonic acid (JA), but not by treatment with salicylic acid (SA). The overexpression of OsMPK4 (oe-MPK4) enhanced constitutive and/or SSB-induced levels of JA, jasmonoyl-l-isoleucine (JA-Ile), ethylene (ET), and SA, as well as the activity of elicited trypsin proteinase inhibitors (TrypPIs), and reduced SSB performance. On the other hand, compared to wild-type plants, oe-MPK4 lines in the greenhouse showed growth retardation. These findings suggest that OsMPK4, by regulating JA-, ET-, and SA-mediated signaling pathways, functions as a positive regulator of rice resistance to the SSB and a negative regulator of rice growth.
Highlights
In their natural habitats, plants often face infestations by various herbivores
Sci. 2018, 19, 1182 from different species revealed that OsMPK4 is homologous to BdMPK6 in Brachypodium distachyon, to SiMPK6 in Setaria italica and to SbMPK6 in Sorghum bicolor; all of these proteins share more than 94% amino acid sequence identity with OsMPK4
OsMPK4 shows homologous to well characterized MPK4 in Arabidopsis thaliana (AtMPK4) [22], Brassica napus (BnMPK4) [41], and Nicotiana tabacum (NtMPK4) [42] (Figure S2), whose amino acid sequence similarities to OsMPK4 were 81.12%, 82.18%, and 81.91%, respectively
Summary
Plants often face infestations by various herbivores. To protect themselves, plants have developed constitutive and induced defensive mechanisms [1,2,3]. In response to the signals, plants activate a defense-related signaling network consisting mainly of jasmonic acid (JA)-, salicylic acid (SA)-, and ethylene (ET)-mediated pathways, and induce the production of defensive compounds; as a result, herbivore resistance in plants increases [4,5,6,7]. During this process, mitogen-activated protein kinase (MPK) cascades play vital roles in the signaling network, functioning upstream and downstream of defense-related signaling pathways [8,9,10,11]. OsMPK3 has been found to negatively regulate the resistance of rice to Magnaporthe oryzae and positively regulate the plant’s tolerance to both drought and submergence [20,21]
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