Reciprocal inhibition of expression between RAV1 and BES1 modulates plant growth and development in Arabidopsis.

RAV1 (Related to ABI3/VP1) is a plant-specific B3 and AP2 domain-containing transcription factor that acts as a negative regulator of growth in many plant species. The expression of RAV1 is downregulated by brassinosteroids (BRs); large-scale transcriptome analyses have shown that the expression of RAV1 was previously targeted by BRI1-EMS-SUPPRESOR1 (BES1) and BRASSINAZOLE-RESISTANT1 (BZR1), which are critical transcription factors for the BR-signaling process. Using RAV1-overexpressing transgenic plants, we showed that RAV1 overexpression reduced the BR signaling capacity, resulting in the downregulation of BR biosynthetic genes and BES1 expression.

Brassinosteroid-Insensitive 1-Associated Receptor Kinase 1 Modulates Abscisic Acid Signaling by Inducing PYR1 Monomerization and Association With ABI1 in .

Brassinosteroid-Insensitive 1-Associated Receptor Kinase 1 (BAK1) is a versatile kinase involved in many different plant developmental responses. Previously, we showed that BAK1 interacts with open stomata 1 (OST1), a cytoplasmic kinase, to promote abscisic acid (ABA)-induced stomatal closure. ABA is a plant hormone that primarily regulates stress responses and is recognized by the PYRABACTIN RESISTANCE1 (PYR1)/PYR1-LIKE (PYL)/REGULATORY COMPONENT OF ABA RECEPTORS (RCAR), which activates ABA signaling.

BAK1-induced RPK1 phosphorylation is essential for RPK1-mediated cell death in Arabidopsis.

Being sessile, plants must deploy highly exquisite systems to respond to various internal and external signals for modulating growth and development throughout their lifespan. Many studies on Arabidopsis have shown that leucine-rich repeat-containing receptor-like kinases, including BRI1-associated receptor kinase 1 (BAK1) and receptor-like protein kinase 1 (RPK1), are suitable for such pleiotropic demands of plants. Previously, BAK1 and RPK1 were independently proven to be involved in the regulation of premature cell death.

Open stomata 1 exhibits dual serine/threonine and tyrosine kinase activity in regulating abscisic acid signaling.

Open Stomata 1 (OST1)/SnRK2.6 is a critical component connecting abscisic acid (ABA) receptor complexes and downstream components, including anion channels and transcription factors. Because OST1 is a serine/threonine kinase, several autophosphorylation sites have been identified, and S175 is known to be critical for its kinase activity.

Receptor-like protein kinases RPK1 and BAK1 sequentially form complexes with the cytoplasmic kinase OST1 to regulate ABA-induced stomatal closure.

Regulation of plant water status occurs via abscisic acid (ABA)-induced stomatal closure. Open Stomata 1 (OST1) is a critical ABA signaling component regulating this process in guard cells. We previously reported that BRI1-associated receptor kinase 1 (BAK1) positively regulates ABA-induced stomatal closure by interacting with and phosphorylating OST1.

Brassinosteroid reduces ABA accumulation leading to the inhibition of ABA-induced stomatal closure.

Proper regulation of stomatal movement in response to various environmental stresses or developmental status is critical for the adaptation of many plant species to land. In plants, abscisic acid (ABA)-induced stomatal closure is a well-adapted method of regulating water status. In addition to ABA, we previously showed that plant-specific steroidal hormone, brassinosteroid (BR), also induces stomatal closure; however, BR modulates ABA-induced stomatal closure negatively at high concentrations.