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Title: The signaling peptide-encoding genes CLE16, CLE17 and CLE27 are dispensable for Arabidopsis shoot apical meristem activity

item GREGORY, ELLEN - University Of California
item ALEXANDER, MARTIN - University Of California
item MILLER, MARK - University Of California
item Fletcher, Jennifer

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2018
Publication Date: 8/17/2018
Citation: Gregory, E., Alexander, M., Miller, M.J., Fletcher, J.C. 2018. The signaling peptide-encoding genes CLE16, CLE17 and CLE27 are dispensable for Arabidopsis shoot apical meristem activity. PLoS One. 13(8):e0202595.

Interpretive Summary: The entire above-ground architecture of a plant, all of the leaves, stems and flowers, are generated by the activity of a pool of stem cells at the growing tip, called the shoot meristem. Our previous research has shown that the CLAVATA3 (CLV3) gene plays a key role in controlling the number of stem cells in the shoot meristem. Knocking out CLV3 activity increases flower, fruit and seed number in the model plant Arabidopsis as well as in corn, rice and tomato, significantly elevating crop plant yield. In this work we identified three Arabidopsis CLV3-related genes, CLE16, CLE17 and CLE27, whose function in controlling shoot meristem activity had not been previously studied. Using the powerful new CRISPR-Cas9 genome editing technology we generated knockout mutations in the three genes and studied their functions during plant development. We found no role for CLE16 or CLE17 in the shoot meristem, whereas CLE27 had a minor function in delaying the transition of the shoot from making leaves to making flowers. Our results indicate that knocking out homologs of CLE16, CLE17 or CLE27 in agricultural plant species one by one is unlikely to be sufficient to improve yield, but that generating knockouts of the genes in combination may prove a more effective strategy for crop improvement.

Technical Abstract: The shoot apical meristem produces all of the leaves, stems and flowers of a flowering plant from a reservoir of stem cells at its growing tip. In Arabidopsis, the small polypeptide signaling molecule CLAVATA3 (CLV3), a member of the CLV3/EMBRYO SURROUNDING REGION-RELATED (CLE) gene family, is a key component of a negative feedback loop that maintains stem cell activity in shoot and floral meristems throughout development. Because in some plant species multiple CLE genes are involved in regulating shoot meristem activity, we tested the hypothesis that CLE genes other than CLV3 might function in stem cell homeostasis in Arabidopsis. We identified three Arabidopsis CLE genes expressed in the post-embryonic SAM, generated loss-of-function alleles using genome editing, and analyzed the meristem phenotypes of the resulting mutant plants. We found that neither CLE16 nor CLE17 affected vegetative or reproductive meristem activity under normal growth conditions. The third gene, CLE27, had no discernable affect on stem cell homeostasis in the shoot apical meristem but played a minor role in repressing the floral transition and inducing axillary meristem formation. Our results indicate that the CLE16, CLE17 and CLE27 genes have largely redundant roles in the Arabidopsis SAM and/or regulate meristem activity only under specific environmental conditions.