RESUMO
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.
Assuntos
Brassinosteroides/metabolismo , Resistência à Doença , Doenças das Plantas/imunologia , Reguladores de Crescimento de Plantas/metabolismo , Proteínas de Plantas/metabolismo , Solanum lycopersicum/fisiologia , Tylenchoidea/fisiologia , Ácido Abscísico/metabolismo , Animais , Ciclopentanos/metabolismo , Etilenos/metabolismo , Regulação da Expressão Gênica de Plantas , Solanum lycopersicum/enzimologia , Solanum lycopersicum/genética , Solanum lycopersicum/imunologia , Proteínas Quinases Ativadas por Mitógeno/genética , Proteínas Quinases Ativadas por Mitógeno/metabolismo , NADPH Oxidases/genética , NADPH Oxidases/metabolismo , Oxilipinas/metabolismo , Doenças das Plantas/parasitologia , Proteínas de Plantas/genética , Espécies Reativas de Oxigênio/metabolismo , Ácido Salicílico/metabolismo , Transdução de SinaisRESUMO
Brassinosteroids (BRs) are essential for plant growth and development; however, their roles in the regulation of stomatal opening or closure remain obscure. Here, the mechanism underlying BR-induced stomatal movements is studied. The effects of 24-epibrassinolide (EBR) on the stomatal apertures of tomato (Solanum lycopersicum) were measured by light microscopy using epidermal strips of wild type (WT), the abscisic acid (ABA)-deficient notabilis (not) mutant, and plants silenced for SlBRI1, SlRBOH1 and SlGSH1. EBR induced stomatal opening within an appropriate range of concentrations, whereas high concentrations of EBR induced stomatal closure. EBR-induced stomatal movements were closely related to dynamic changes in H(2)O(2) and redox status in guard cells. The stomata of SlRBOH1-silenced plants showed a significant loss of sensitivity to EBR. However, ABA deficiency abolished EBR-induced stomatal closure but did not affect EBR-induced stomatal opening. Silencing of SlGSH1, the critical gene involved in glutathione biosynthesis, disrupted glutathione redox homeostasis and abolished EBR-induced stomatal opening. The results suggest that transient H(2)O(2) production is essential for poising the cellular redox status of glutathione, which plays an important role in BR-induced stomatal opening. However, a prolonged increase in H(2)O(2) facilitated ABA signalling and stomatal closure.
Assuntos
Brassinosteroides/farmacologia , Peróxido de Hidrogênio/metabolismo , Estômatos de Plantas/fisiologia , Solanum lycopersicum/fisiologia , Esteroides Heterocíclicos/farmacologia , Ácido Abscísico/farmacologia , Inativação Gênica/efeitos dos fármacos , Glutationa/farmacologia , Solanum lycopersicum/efeitos dos fármacos , Solanum lycopersicum/enzimologia , Modelos Biológicos , Movimento/efeitos dos fármacos , NADPH Oxidases/metabolismo , Oxirredução/efeitos dos fármacos , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Estômatos de Plantas/citologia , Estômatos de Plantas/efeitos dos fármacos , Estômatos de Plantas/enzimologiaRESUMO
Negative plant-soil feedbacks play an important role in soil sickness, which is one of the factors limiting the sustainable development of intensive agriculture. Various factors, such as the buildup of pests in the soil, disorder in physico-chemical soil properties, autotoxicity, and other unknown factors may contribute to soil sickness. A range of autotoxins have been identified, and these exhibit their allelopathic potential by influencing cell division, water and ion uptake, dark respiration, ATP synthesis, redox homeostasis, gene expression, and defense responses. Meanwhile, there are great interspecific and intraspecific differences in the uptake and accumulation of autotoxins, which contribute to the specific differences in growth in response to different autotoxins. Importantly, the autotoxins also influence soil microbes and vice versa, leading to an increased or decreased degree of soil sickness. In many cases, autotoxins may enhance soilborne diseases by predisposing the roots to infection by soilborne pathogens through a direct biochemical and physiological effect. Some approaches, such as screening for low autotoxic potential and disease-resistant genotypes, proper rotation and intercropping, proper soil and plant residue management, adoption of resistant plant species as rootstocks, introduction of beneficial microbes, physical removal of phytotoxins, and soil sterilization, are proposed. We discuss the challenges that we are facing and possible approaches to these.
