Abstract
Brassinosteroids (BRs) are a group of plant steroid hormones that play important roles in regulating plant development. In addition, BRs show considerable functional redundancy with other plant hormones such as gibberellins (GAs). BRASSINAZOLE RESISTANT1 (BZR1) and BRI1-EMS-SUPPRESSOR1 (BES1) transcription factors are negative feedback regulators of BR biosynthesis. This study provides evidence for the roles of MdBZR1 and MdBZR1-2like in promoting GA production. These results also show that BRs regulate GA biosynthesis to improve salt tolerance in apple calli. Moreover, this research proposes a regulatory model, in which MdBZR1 and MdBZR1-2like bind to the promoters of GA biosynthetic genes to regulate their expression in a BR-dependent manner. The expression of key GA biosynthetic genes, MdGA20ox1, MdGA20ox2, and MdGA3ox1 in yeast helps to maintain normal growth even under intense salt stress. In summary, this study underscores the roles of MdBZR1 and MdBZR1-2like in improving salt tolerance by regulating GA biosynthesis in apple calli.
Highlights
Brassinosteroids (BRs) are sterol-derived phytohormones that regulate plant growth and development; their structures are similar to animal steroid hormones (Mitchell et al, 1970; Husna et al, 2018)
We report that MdBZR1 and MdBZR1-2like could bind to the promoters of both MdGA20ox2 and MdGA3ox1 and enhance their expressions in apple
BR Signaling Regulates the Transcript Levels of MdGA20ox1, MdGA20ox2, and MdGA3ox1 In Arabidopsis, it has long been known that BRs and GAs function redundantly in many developmental programs, and the crosstalk between these two hormonal pathways occurs on the transcriptional level (Gallego-Bartolomé et al, 2012; BernardoGarcía et al, 2014)
Summary
Brassinosteroids (BRs) are sterol-derived phytohormones that regulate plant growth and development; their structures are similar to animal steroid hormones (Mitchell et al, 1970; Husna et al, 2018). In Arabidopsis, the BRASSINOSTEROID INSENSITIVE-1 (BRI1) receptor kinase functions at the first step of BR signaling. In the absence of upstream BR signals, two BR-responsive transcription factors, BRASSINAZOLE RESISTANT-1 (BZR1) and BRI1-EMS-SUPPRESSOR-1 (BES1), are phosphorylated by BIN2, causing BZR1 and BES1 to be trapped in the cytoplasm due to the loss of their DNA binding abilities (Kim et al, 2018). In the presence of BRs, the binding of BR to BRI1 induces the phosphorylation of BRI1 by its receptor kinase BRI1-ASSOCIATED RECEPTOR KINASE1 (BAK1), leading to the disassociation of BKI1 and BRI1. This causes BRI1 to pass the signal to BR SIGNALING KINASE1
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