Abstract
Brassinosteroids (BRs), plant steroid hormones, play essential roles in modulating cell elongation, vascular differentiation, senescence, and stress responses. However, the mechanisms by which BRs regulate plant mitochondria and resistance to abiotic stress remain largely unclear. Mitochondrial alternative oxidase (AOX) is involved in the plant response to a variety of environmental stresses. In this report, the role of AOX in BR-induced tolerance against cold, polyethylene glycol (PEG), and high-light stresses was investigated. Exogenous applied brassinolide (BL, the most active BR) induced, while brassinazole (BRZ, a BR biosynthesis inhibitor) reduced alternative respiration and AOX1 expression in Nicotiana benthamiana. Chemical scavenging of H2O2 and virus-induced gene silencing (VIGS) of NbRBOHB compromised the BR-induced alternative respiratory pathway, and this result was further confirmed by NbAOX1 promoter analysis. Furthermore, inhibition of AOX activity by chemical treatment or a VIGS-based approach decreased plant resistance to environmental stresses and compromised BR-induced stress tolerance. Taken together, our results indicate that BR-induced AOX capability might contribute to the avoidance of superfluous reactive oxygen species accumulation and the protection of photosystems under stress conditions in N. benthamiana.
Highlights
During growth and development, plants have to cope with a variety of biotic and abiotic stresses
In order to investigate the relationship between reactive oxygen species (ROS) and alternative pathway in BR signalling, we compared the time course of changes on Valt, H2O2 accumulation, and transcripts levels of NbAOX1, NbRBOHA, and NbRBOHB after BL treatment in N. benthamiana
To determine the role of the alternative oxidase (AOX) pathway in BR-induced stress tolerance, we investigated the function of photosystem II (PSII) under stress conditions, as chlorophyll fluorescence quenching analysis has been proven to be a powerful and reliable method to assess changes in the function of PSII in the alleviated the significant decline of Fv/Fm and increase of non-photochemical quenching (NPQ) in Tobacco rattle virus (TRV):00 plants under stress conditions, and these protective effects were again blocked in TRV:NbAOX1 plants (Fig. 7)
Summary
Plants have to cope with a variety of biotic (i.e. viruses, bacteria, fungi, and insects) and abiotic (i.e. drought, salt, wounding, and changes in temperature and light) stresses To survive such environmental stress, plants have developed elaborate mechanisms to perceive external signals and manifest adaptive responses to environmental changes. BRs signal through receptor kinase BRI1, co-receptor BAK1, and several other signalling components to control BRI1 EMS suppressor 1 (BES1) and brassinazole resistant 1 (BZR1) family transcription factors that modulate thousands of target genes (Wang et al, 2002; Yin et al, 2002; Yu et al, 2011; Zhang et al, 2014a) In addition to their pivotal role in plant growth and development, BRs appear to protect plants from a variety of environmental stresses. The mechanisms by which BRs enhance plant stress tolerance have so far remained largely unknown
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