RESUMO
Plants generate reactive oxygen species (ROS) in the apoplast in response to pathogen attack, especially following resistance (R) gene-mediated pathogen recognition; however, the mechanisms activating ROS generation remain unknown. Here, we demonstrate that RKN (Meloidogyne incognita) infection rapidly induces ROS accumulation in the roots of tomato (Solanum lycopersicum) plants that contain the R gene Mi-1.2 but rarely induces ROS accumulation in the susceptible or Mi-1.2-silenced resistant genotypes. RNK also induces the hypersensitive response, a form of programmed cell death, in Mi-1.2 plants. RKN induces the expression of numerous class-A heat shock factor (HsfA) genes in resistant tomato plants. Silencing HsfA1a compromises Mi-1.2-mediated resistance, apoplastic H2O2 accumulation, and the transcription of whitefly induced 1 (Wfi1), which encodes a respiratory burst oxidase homolog. HsfA1a regulates Wfi1 transcription by binding to the Wfi1 promoter, and silencing of Wfi1 compromises Mi-1.2-mediated resistance. HsfA1a and Wfi1 are involved in Mi-1.2-triggered Hsp90 accumulation and basal defense in susceptible tomato. Thus, HsfA-1aWfi1-dependent ROS signaling functions as a crucial regulator of plant defense responses.
Assuntos
Fatores de Transcrição de Choque Térmico/metabolismo , Proteínas de Plantas/genética , Solanum lycopersicum/genética , Solanum lycopersicum/parasitologia , Tylenchoidea/patogenicidade , Animais , Regulação da Expressão Gênica de Plantas , Proteínas de Choque Térmico HSP90/genética , Proteínas de Choque Térmico HSP90/metabolismo , Fatores de Transcrição de Choque Térmico/genética , Interações Hospedeiro-Parasita/genética , Peróxido de Hidrogênio/metabolismo , Proteínas de Plantas/metabolismo , Raízes de Plantas/genética , Raízes de Plantas/metabolismo , Raízes de Plantas/parasitologia , Plantas Geneticamente Modificadas , Regiões Promotoras Genéticas , Espécies Reativas de Oxigênio/metabolismoRESUMO
Interplay of hormones with reactive oxygen species (ROS) fine-tunes the response of plants to stress; however, the crosstalk between brassinosteroids (BRs) and ROS in nematode resistance is unclear. In this study, we found that low BR biosynthesis or lack of BR receptor increased, whilst exogenous BR decreased the susceptibility of tomato plants to Meloidogyne incognita. Hormone quantification coupled with hormone mutant complementation experiments revealed that BR did not induce the defence response by triggering salicylic acid (SA), jasmonic acid/ethylene (JA/ET) or abscisic acid (ABA) signalling pathway. Notably, roots of BR-deficient plants had decreased apoplastic ROS accumulation, transcript of RESPIRATORY BURST OXIDASE HOMOLOG1 (RBOH1) and WHITEFLY INDUCED1 (WFI1), and reduced activation of mitogen-activated protein kinase 1/2 (MPK1/2) and MPK3. Silencing of RBOH1, WFI1, MPK1, MPK2 and MPK3 all increased the root susceptibility to nematode and attenuated BR-induced resistance against the nematode. Significantly, suppressed transcript of RBOH1 compromised BR-induced activation of MPK1/2 and MPK3. These results strongly suggest that RBOH-dependent MPK activation is involved in the BR-induced systemic resistance against the nematode.