We hypothesize that these homo- and heteromeric complexes may differentially regulate distal root meristem maintenance. We conclude that essential components of the ancestral shoot stemness regulatory system also act in the root and that the specific interaction of CLV1 with ACR4 serves to moderate and control stemness homeostasis in the root meristem. The structural differences between these two meristem types may have necessitated this recruitment of ACR4 for signaling by CLV1.

Stem cell homeostasis in plant shoot meristems requires tight coordiantion between stem cell proliferation and cell differentiation. In Arabidopsis, stem cells express the secreted dodecapeptide CLAVATA3 (CLV3), which signals through the leucine-rich repeat (LRR)-receptor kinase CLAVATA1 (CLV1) and related CLV1-family members to downregulate expression of the homeodomain transcription factor WUSCHEL (WUS). WUS protein moves from cells below the stem cell domain to the meristem tip and promotes stem cell identity, together with CLV3 expression, generating a negative feedback loop. How stem cell activity in the meristem centre is coordinated with organ initiation and cell differentiation at the periphery is unknown. We show here that the CLE40 gene, encoding a secreted peptide closely related to CLV3, is expressed in the SAM in differentiating cells in a pattern complementary to that of CLV3. CLE40 promotes WUS expression via BAM1, a CLV1-family receptor, and CLE40 expression is in turn repressed in a WUS-dependent manner. Together, CLE40-BAM1-WUS establish a second negative feedback loop. We propose that stem cell homeostasis is achieved through two intertwined pathways that adjust WUS activity and incorporate information on the size of the stem cell domain, via CLV3-CLV1, and on cell differentiation via CLE40-BAM1.

HighlightInformation collected using antagonistic peptide approaches can be very useful, but these approaches do not work in all cases and require insight on ligand-receptor interactions and peptide ligand structure.

The receptor-like kinases (RLKs) CLAVATA1 (CLV1) and BARELY ANY MERISTEMs (BAM1–BAM3) form the CLV1 family (CLV1f), which perceives peptides of the CLV3/EMBRYO SURROUNDING REGION (ESR)-related (CLE) family within various signaling pathways of Arabidopsis thaliana. CLE peptide signaling, which is required for meristem size control, vascular development, and pathogen responses, involves the formation of receptor complexes at the plasma membrane. These complexes comprise RLKs and co-receptors in varying compositions depending on the signaling context, and regulate expression of target genes, such as WUSCHEL (WUS). How the CLE signal is transmitted intracellularly after perception at the plasma membrane is not known in detail. Here, we found that the membrane-associated receptor-like cytoplasmic kinase (RLCK) MAZZA (MAZ) and additional members of the Pti1-like protein family interact in vivo with CLV1f receptors. MAZ, which is widely expressed throughout the plant, localizes to the plasma membrane via post-translational palmitoylation, potentially enabling stimulus-triggered protein re-localization. We identified a role for a CLV1–MAZ signaling module during stomatal and root development, and redundancy could potentially mask other phenotypes of maz mutants. We propose that MAZ, and related RLCKs, mediate CLV1f signaling in a variety of developmental contexts, paving the way towards understanding the intracellular processes after CLE peptide perception.

Stem cell homeostasis in plant shoot meristems requires tight coordination between stem cell proliferation and cell differentiation. In Arabidopsis, stem cells express the secreted dodecapeptide CLAVATA3 (CLV3), which signals through the leucine-rich repeat (LRR)–receptor kinase CLAVATA1 (CLV1) and related CLV1-family members to downregulate expression of the homeodomain transcription factor WUSCHEL (WUS). WUS protein moves from cells below the stem cell domain to the meristem tip and promotes stem cell identity, together with CLV3 expression, generating a negative feedback loop. How stem cell activity in the meristem centre is coordinated with organ initiation and cell differentiation at the periphery is unknown. We show here that the CLE40 gene, encoding a secreted peptide closely related to CLV3, is expressed in the SAM in differentiating cells in a pattern complementary to that of CLV3. CLE40 promotes WUS expression via BAM1, a CLV1-family receptor, and CLE40 expression is in turn repressed in a WUS-dependent manner. Together, CLE40-BAM1-WUS establish a second negative feedback loop. We propose that stem cell homeostasis is achieved through two intertwined pathways that adjust WUS activity and incorporate information on the size of the stem cell domain, via CLV3-CLV1, and on cell differentiation via CLE40-BAM1.

The interaction between phosphorus (P) and other media components alters root development and masks the plant response and thus limits the ability to correctly identify P-deficiency response (pdr) mutants. This study aims to assess changes in root development caused by different composition of growth media normally used in Arabidopsis research and to study their effects on pdr-mutant screening. Primary root growth of four genotypes was analyzed in media differing in P concentrations: half-strength Murashige and Skoog (½ MS) and Somerville and Ogren (SO). The effects of nitrogen source and Fe on root growth were investigated in each medium separately and in a mixture. We found that the primary root length of all genotypes grown on ½ MS was reduced in comparison with plants grown on SO medium. The mutant pdr9 was the most sensitive in ½ MS, This mutant was also hypersensitive to Fe that intensified its sensitivity to ammonium. Ammonium increased the root inhibition caused by Fe also in wild-type plants. In conclusion, on the basis of our study we recommend to use SO medium, which ensures an efficient selection to screen for pdr mutants through root growth. Moreover, nitrogen sources in the media other than nitrate should be taken carefully.

The receptor-like kinases (RLKs) CLAVATA1 (CLV1) and BARELY ANY MERISTEMs (BAM1 – 3) form the CLV-family (CLVf), which perceives peptides of the CLV3/EMBRYO SURROUNDING REGION (ESR)-related (CLE) family within various signaling pathways of Arabidopsis thaliana. CLE peptide signaling, which is required for meristem size control, vascular development, or pathogen responses, involves the formation of receptor complexes at the plasma membrane (PM). These complexes comprise RLKs and co-receptors in varying compositions depending on the signaling context and regulate target gene expression, such as WUSCHEL (WUS). How the CLE signal is transmitted intracellularly after perception at the PM is not known.Here, we found that the membrane-associated receptor-like cytoplasmic kinase (RLCK) MAZZA (MAZ) MAZ and additional members of the Pti1-like protein family interact in vivo with CLVf receptors. MAZ, which is widely expressed throughout the plant, localizes to the PM via posttranslational palmitoylation potentially enabling stimulus-triggered protein re-localization. We identified a role for a CLV1/MAZ signaling module during stomatal and root development, and redundancy could potentially mask other phenotypes of maz-1 mutants. We propose that RLCKs such as MAZ mediate CLVf signaling in a variety of developmental contexts, paving the way towards understanding the intracellular processes after CLE peptide perception.

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