Joe Kieber: Cytokinin signaling and function across the monocot/dicot divide

Cytokinin is a phytohormone that plays a major role in the growth, development, and reproduction of plants. Most of the work aimed at understanding this pathway has been done in the dicot model system Arabidopsis thaliana, but the world’s major cereal species are monocots. Following up on our work in Arabidopsis, we are using rice as a model system to explore cytokinin signaling and function in a monocot. Using a CRISPR/Cas9 approach, we have disrupted all predicted cytokinin signaling elements in rice in various multiple mutant combinations and are characterizing the effects of these mutations on rice growth and development. One focus has been on the four-member cytokinin HK receptor gene family. The HKs redundantly regulate cytokinin sensitivity in rice. We find that the four HKs play distinct but overlapping roles in multiple aspects of rice development; some of these roles are shared with Arabidopsis, some are similar but more prominent in rice, and some are unique to rice. Finally, unlike what we observe in Arabidopsis, disruption of all four cytokinin receptor HKs in rice results in shootless phenotype, and the HKs, and by inference cytokinin, is essential for the establishment of the shoot apical meristem in rice embryos. Finally, we are using single nuclei approaches to discern how cytokinin regulates the vegetative and inflorescence meristems.