Cold Spring Harbor Lab, New York, NY 11724, USA
Shoot growth depends upon meristems, pools of stem cells that are maintained in a number of ways, including a negative feedback loop between the CLAVATA pathway and the WUSCHEL homeobox gene. CLAVATA signaling involves a secreted peptide, CLAVATA3 (CLV3), and its perception by cell surface leucine-rich repeat (LRR) receptors, including the CLV1 receptor kinase, and an LRR receptor-like protein, CLV2. We are interested in finding novel players in the CLV-WUS pathway, as well as new regulators that could affect meristem size in parallel pathways. Maize provides a rich source of new information, because there are many clavata-type mutants, and their isolation is becoming routine. We isolated the maize COMPACT PLANT2 (CT2) gene, and it encodes the predicted α subunit (Gα) of a heterotrimeric GTP binding protein. ct2 mutants have CLAVATA-like meristem proliferation phenotypes, and genetic, biochemical and functional assays indicate that CT2/Gα signaling transmits a stem cell restrictive signal from a maize CLAVATA LRR receptor, suggesting a new function for Gα signaling in plants. Recent studies have questioned the idea that plant heterotrimeric G proteins interact with canonical GPCRs, and our findings suggest that single pass LRR receptors act as GPCRs in plants, challenging the dogma that GPCRs are exclusively 7TM proteins. We have also identified new regulators of maize shoot meristem size, including a new CLV-related receptor, FEA3, that appears to function in a different pathway to control meristem size in parallel to CLV-WUS. We believe that FEA3 responds to a CLV3-related ligand that is expressed in differentiating cells, so it could provide a feedback from primordia to the meristem, The roles of these genes will be discussed, as well as their potential use in improvement of maize yields, for example through control of seed yield.