*Review* **Linking Brassinosteroid and ABA Signaling in the Context of Stress Acclimation**

**Victor P. Bulgakov 1,\* and Tatiana V. Avramenko 1,2**


Received: 2 July 2020; Accepted: 17 July 2020; Published: 20 July 2020

**Abstract:** The important regulatory role of brassinosteroids (BRs) in the mechanisms of tolerance to multiple stresses is well known. Growing data indicate that the phenomenon of BR-mediated drought stress tolerance can be explained by the generation of stress memory (the process known as 'priming' or 'acclimation'). In this review, we summarize the data on BR and abscisic acid (ABA) signaling to show the interconnection between the pathways in the stress memory acquisition. Starting from brassinosteroid receptors brassinosteroid insensitive 1 (BRI1) and receptor-like protein kinase BRI1-like 3 (BRL3) and propagating through BR-signaling kinases 1 and 3 (BSK1/3) → BRI1 suppressor 1 (BSU1) — brassinosteroid insensitive 2 (BIN2) pathway, BR and ABA signaling are linked through BIN2 kinase. Bioinformatics data sugges<sup>t</sup> possible modules by which BRs can a ffect the memory to drought or cold stresses. These are the BIN2 → SNF1-related protein kinases (SnRK2s) → abscisic acid responsive elements-binding factor 2 (ABF2) module; BRI1-EMS-supressor 1 (BES1) or brassinazole-resistant 1 protein (BZR1)–TOPLESS (TPL)–histone deacetylase 19 (HDA19) repressor complexes, and the BZR1/BES1 → flowering locus C (FLC)/flowering time control protein FCA (FCA) pathway. Acclimation processes can be also regulated by BR signaling associated with stress reactions caused by an accumulation of misfolded proteins in the endoplasmic reticulum.

**Keywords:** ABA signaling; brassinosteroid signaling cascade; drought tolerance; priming; stress adaptation; stress memory
