Abstract
Stem cell maintenance in plants depends on the activity of small secreted signaling peptides of the CLAVATA3/EMBRYO SURROUNDING REGION (CLE) family, which, in the shoot, act through at least three kinds of receptor complexes, CLAVATA1 (CLV1) homomers, CLAVATA2 (CLV2) / CORYNE (CRN) heteromers, and CLV1/CLV2/CRN multimers. In the root, the CLV2/CRN receptor complexes function in the proximal meristem to transmit signals from the CLE peptide CLE40. While CLV1 consists of an extracellular receptor domain and an intracellular kinase domain, CLV2, a leucine-rich repeat (LRR) receptor-like protein, and CRN, a protein kinase, have to interact to form a receptor-kinase complex. The kinase domain of CRN has been reported to be catalytically inactive, and it is not yet known how the CLV2/CRN complex can relay the perceived signal into the cells, and whether the kinase domain is necessary for signal transduction at all. In this study we show that the kinase domain of CRN is actively involved in CLV3 signal transduction in the shoot apical meristem of Arabidopsis, but it is dispensable for CRN protein function in root meristem maintenance. Hence, we provide an example of a catalytically inactive pseudokinase that is involved in two homologous pathways, but functions in distinctively different ways in each of them.
Highlights
In Arabidopsis thaliana all tissues are derived from the activities of the stem cell populations of the meristem (Nägeli, 1858)
In this study we show that the kinase domain of CRN is actively involved in CLV3 signal transduction in the shoot apical meristem of Arabidopsis, but it is dispensable for CRN protein function in root meristem maintenance
A second available mutant crn allele is crn-3, which is in the Columbia-0 (Col) background. This line was identified as an EMS-induced mutant in the Arabidopsis TILLING project and subsequently backcrossed three times to clean-up the genetic background for any additional mutations (Till et al, 2003). clv mutants in the Col background typically exhibit weaker phenotypes compared to alleles in the Landsberg erecta (Ler) background (Müller et al, 2008)
Summary
In Arabidopsis thaliana all tissues are derived from the activities of the stem cell populations of the meristem (Nägeli, 1858). Stem cell homeostasis in the shoot apical meristem (SAM) depends on the activity of the CLAVATA (CLV)– WUSCHEL (WUS) negative feedback loop (Brand et al, 2000; Schoof et al, 2000). CLV3 signals from the stem cell domain mainly through the receptors CLAVATA1 (CLV1), CLAVATA2 (CLV2) and CORYNE (CRN) to restrict WUS expression, establishing a negative feedback loop (Brand et al, 2000; Schoof et al, 2000). Plants carrying mutations in CLV1, CLV2, or CRN generate more stem cells due to less restricted WUS expression, which results in a larger meristem that subsequently
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