Shoot growth depends upon meristems, pools of stem cells that are maintained by a negative feedback loop between the CLAVATA pathway and the WUSCHEL transcription factor. 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 is an excellent model system for these studies, because there are many clavata- type mutants that define new functions. For example, we isolated the COMPACT PLANT2 (CT2) gene, and found it encodes G, the predicted subunit of a heterotrimeric GTP binding protein. ct2 mutants have meristem proliferation phenotypes, and multiple assays indicate that CT2/G signaling transmits a stem cell restrictive signal from a maize CLAVATA LRR receptor, suggesting a new function for G in plants. We also characterized a new CLV- related receptor, FASCIATED EAR3 (FEA3), that appears to function in parallel to CLV-WUS to provide a different mode of feedback to the stem cell niche.
Despite these exciting new findings, our understanding of signaling pathways in plants is incomplete, because many factors are obscured by genetic redundancy. I will discuss the application of CRISPR in countering genetic redundancy and in understanding compensation mechanisms in plants. We use single-cell RNA-sequencing to enable a cell-by-cell reconstruction of gene expression in shoot meristems. Multiplex CRISPR knockouts are then used to address redundancy, with guideRNA constructs targeting multiple paralogs at once. We also use CRISPR of promoters to generate weak alleles, corresponding to the type of variation expected to occur in natural plant populations. These weak promoter alleles mildly increase meristem size and enhance seed production, and may be useful in improvement of crop yields.
Dave Jackson is a Professor of Plant Genetics at Cold Spring Harbor Laboratory, NY, USA. His lab finds and studies the genes that control plant growth and architecture. They have discovered genes that control stem cell proliferation, including a heterotrimeric G protein that interacts with a completely different class of receptors than in animals, and other master regulators of development and cell to cell signaling. His work has also demonstrated that weak mutations in developmental genes can enhance seed production in maize, leading to potential crop yield increases, and they are now using genome editing to improve crop yield traits. His lab also develops maize genomics tools and is characterizing global gene expression networks that have revealed new hypotheses in control of inflorescence development. Since 2015, Jackson has also served as a Chang Jiang Visiting Professor at Huazhong Agricultural University, Wuhan, China. Further information is available at http://jacksonlab.labsites.cshl.edu/.