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.
Highlights
Eukaryotic protein kinases form a large superfamily, and are associated essentially with all cellular functions
Cell-to-cell communication as well as innate immunity rely on plant receptor-like kinases (RLKs), which account for more than half of protein kinases in Arabidopsis (>600 RLK genes out of >1000 kinase-coding genes)
RLKs exhibit serine/threonine kinase specificity in contrast to animal receptor kinases that are almost exclusively tyrosine kinases. This indicates that ancient RLK/Pelle kinases were co-opted for transmembrane signalling in plants after their divergence from animals
Summary
Eukaryotic protein kinases form a large superfamily, and are associated essentially with all cellular functions. The number of protein kinase coding genes is especially high in plant genomes. 2% in Homo sapiens [1] This high number of protein kinases is likely due to the importance of cell-to-cell communication during the post-embryonic development of plants that is strongly influenced by the environment. Cell-to-cell communication as well as innate immunity rely on plant receptor-like kinases (RLKs), which account for more than half of protein kinases in Arabidopsis (>600 RLK genes out of >1000 kinase-coding genes). RLKs exhibit serine/threonine kinase specificity in contrast to animal receptor kinases that are almost exclusively tyrosine kinases. This indicates that ancient RLK/Pelle kinases were co-opted for transmembrane signalling in plants after their divergence from animals
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