The Arabidopsis RLCK VI_A2 Kinase Controls Seedling and Plant Growth in Parallel with Gibberellin

Abstract

The plant-specific receptor-like cytoplasmic kinases (RLCKs) form a large, poorly characterized family. Members of the RLCK VI_A class of dicots have a unique characteristic: their activity is regulated by Rho-of-plants (ROP) GTPases. The biological function of one of these kinases was investigated using a T-DNA insertion mutant and RNA interference. Loss of RLCK VI_A2 function resulted in restricted cell expansion and seedling growth. Although these phenotypes could be rescued by exogenous gibberellin, the mutant did not exhibit lower levels of active gibberellins nor decreased gibberellin sensitivity. Transcriptome analysis confirmed that gibberellin is not the direct target of the kinase; its absence rather affected the metabolism and signalling of other hormones such as auxin. It is hypothesized that gibberellins and the RLCK VI_A2 kinase act in parallel to regulate cell expansion and plant growth. Gene expression studies also indicated that the kinase might have an overlapping role with the transcription factor circuit (PIF4-BZR1-ARF6) controlling skotomorphogenesis-related hypocotyl/cotyledon elongation. Furthermore, the transcriptomic changes revealed that the loss of RLCK VI_A2 function alters cellular processes that are associated with cell membranes, take place at the cell periphery or in the apoplast, and are related to cellular transport and/or cell wall reorganisation.

Advances in the Molecular Mechanisms of Abscisic Acid and Gibberellins Functions in Plants

“…The reviews published in this issue focus on the interaction between ABA and GAs in regulating non climacteric fruit development and maturation [ 7 ], current knowledge on the role of ABA in mediating mechanisms whereby grapevine deals with abiotic stresses [ 8 ], the analysis of the role of ABA in flowering transition [ 9 ], the mechanism by which the type 2C Protein Phosphatases (PP2C) gene transcription modulates ABA signaling [ 10 ], and the role of the Mediator complex on the ABA signaling pathway and abiotic stress response [ 11 ]. The original research articles investigate the causes and consequences of the kaolin-induced modulation of ABA biosynthesis in grapevines when faced with a water deficit [ 12 ], the involvement of ABA in plant immune responses [ 13 ], and the relation between GAs and Arabidopsis receptor-like cytoplasmic kinase (RLCK) VI_A2 [ 14 ]. In this editorial, I summarize the main findings of these eight insightful works.…”

“…Valkai et al [ 14 ] investigate the biological function of the Arabidopsis RLCK VI_A2 gene in the regulation of plant growth and skotomorphogenesis. RLCK VI_A2 is a member of the plant-specific receptor-like cytoplasmic kinases (RLCKs) that form a large and barely characterized family.…”

“…The activity of the RLCK VI_A class of dicots is regulated by Rho-of-plants (ROP) GTPases. Valkai et al [ 14 ] show that loss of the RLCK VI_A2 function leads to reduced cell expansion and seedling growth. These mutant phenotypes can be rescued by the exogenous application of GAs.…”