BRASSINAZOLE RESISTANT 1 (BZR1), the critical regulator of brassinosteroid (BR) response, participates in various BR-mediated developmental processes. However, the roles of BZR1 in stress tolerance are less clear. Here, we found that BZR1-like protein in tomato controls BR response and is involved in thermotolerance by regulating the FERONIA (FER) homologs. The CRISPR-bzr1 mutant showed reduced growth and was not responsive to 24-epibrassinolide (EBR) with regard to the promotion of plant growth. Mutation in BZR1 impaired the induction of RESPIRATORY BURST OXIDASE HOMOLOG1 (RBOH1), production of H2O2 in the apoplast and heat tolerance. Exogenous H2O2 recovered the heat tolerance of the tomato bzr1 mutant. Overexpression of BZR1 enhanced the production of apoplastic H2O2 and heat stress responses. However, silencing of RBOH1 abolished the BZR1-mediated heat tolerance. Further analysis showed that BZR1 bound to the promoters of FERONIA2 (FER2) and FER3 and induced their expression. Silencing of FER2/3 suppressed BZR1-dependent BR signaling for the induction of RBOH1 transcripts, accumulation of apoplastic H2O2 and heat tolerance. These results indicate that BZR1 regulates heat stress responses in tomato through RBOH1-dependent reactive oxygen species (ROS) signaling, which is at least partially mediated by FER2 and FER3.
BackgroundPlants attenuate their responses to a variety of bacterial and fungal pathogens, leading to higher incidences of pathogen infection at night. However, little is known about the molecular mechanism responsible for the light-induced defence response; transcriptome data would likely facilitate the elucidation of this mechanism.ResultsIn this study, we observed diurnal changes in tomato resistance to Pseudomonas syringae pv. tomato DC3000 (Pto DC3000), with the greatest susceptibility before midnight. Nightly light treatment, particularly red light treatment, significantly enhanced the resistance; this effect was correlated with increased salicylic acid (SA) accumulation and defence-related gene transcription. RNA-seq analysis revealed that red light induced a set of circadian rhythm-related genes involved in the phytochrome and SA-regulated resistance response. The biosynthesis and signalling pathways of multiple plant hormones (auxin, SA, jasmonate, and ethylene) were co-ordinately regulated following Pto DC3000 infection and red light, and the SA pathway was most significantly affected by red light and Pto DC3000 infection. This result indicates that SA-mediated signalling pathways are involved in red light-induced resistance to pathogens. Importantly, silencing of nonexpressor of pathogensis-related genes 1 (NPR1) partially compromised red light-induced resistance against Pto DC3000. Furthermore, sets of genes involved in redox homeostasis (respiratory burst oxidase homologue, RBOH; glutathione S-transferases, GSTs; glycosyltransferase, GTs), calcium (calmodulin, CAM; calmodulin-binding protein, CBP), and defence (polyphenol oxidase, PPO; nudix hydrolase1, NUDX1) as well as transcription factors (WRKY18, WRKY53, WRKY60, WRKY70) and cellulose synthase were differentially induced at the transcriptional level by red light in response to pathogen challenge.ConclusionsTaken together, our results suggest that there is a diurnal change in susceptibility to Pto DC3000 with greatest susceptibility in the evening. The red light induced-resistance to Pto DC3000 at night is associated with enhancement of the SA pathway, cellulose synthase, and reduced redox homeostasis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1228-7) contains supplementary material, which is available to authorized users.
The control of apical dominance involves auxin, strigolactones (SLs), cytokinins (CKs), and sugars, but the mechanistic controls of this regulatory network are not fully understood. Here, we show that brassinosteroid (BR) promotes bud outgrowth in tomato through the direct transcriptional regulation of BRANCHED1 (BRC1) by the BR signaling component BRASSINAZOLE-RESISTANT1 (BZR1). Attenuated responses to the removal of the apical bud, the inhibition of auxin, SLs or gibberellin synthesis, or treatment with CK and sucrose, were observed in bud outgrowth and the levels of BRC1 transcripts in the BR-deficient or bzr1 mutants. Furthermore, the accumulation of BR and the dephosphorylated form of BZR1 were increased by apical bud removal, inhibition of auxin, and SLs synthesis or treatment with CK and sucrose. These responses were decreased in the DELLA-deficient mutant. In addition, CK accumulation was inhibited by auxin and SLs, and decreased in the DELLA-deficient mutant, but it was increased in response to sucrose treatment. CK promoted BR synthesis in axillary buds through the action of the type-B response regulator, RR10. Our results demonstrate that BR signaling integrates multiple pathways that control shoot branching. Local BR signaling in axillary buds is therefore a potential target for shaping plant architecture.
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