Intellectual merit: Besides cell differentiation, stage-specific and localized cell division is also critical to the formation of normal tissues, organs, and organisms. The highly coordinated cell differentiation and proliferation events during growth and development illustrate the importance of cell-cell communication, which is carried out by cell surface receptors/sensors and intracellular signaling components. In Arabidopsis, ERECTA (ER), a receptor-like kinase, and its homologs (ERL1 and ERL2) play important roles in these processes. Their mutation alters both the architecture and the reproduction of the plant. Similar to er or er/erl1/erl2 mutant plants, loss-of-function of MPK3 and MPK6, two Arabidopsis mitogen-activated protein kinases (MAPKs), or their upstream MAPKKs (MKK4/MKK5) also resulted in similar phenotypes. Genetic analysis demonstrated that the gain-of-function MAPKK transgene can rescue the loss-of-function er or er/erl1/erl2 mutants, suggesting that MPK3/MPK6 function downstream of ER/ERL1/ERL2 receptors. The goal of this project is to understand the molecular mechanism underlying the function of MPK3/MPK6 in the regulation of localized cell division. In addition, the MAPKK kinase(s) upstream of the MKK4/MKK5-MPK3/MPK6 module will be identified. A combinatory approach will be employed to reach these goals. Defining a specific MAPK cascade downstream of the well-characterized ER/ERL1/ERL2 receptor-like kinases is important to our understanding of cell-cell communication. The identification of new components downstream of MPK3/MPK6 in the ER/ERL1/ERL2 pathway will reveal the molecular mechanism underlying their role in the localized cell division. The research will also reveal the functional diversity and signaling specificity of MPK3 and MPK6. The tools generated in this project will have broad applications and will be shared with other groups.
Broader impacts: This project will use an integrative approach to understand the roles of a MAPK cascade and its upstream receptor-like kinases in coordinating plant development, which will serve as an excellent training environment for students and postdoctoral fellows. Training in use of integrative approaches to the study of biological phenomena is critical to the advancement of post-genome biology. In addition to scientific methodology, students/post-docs will also receive training in ethics and career development. Students (both graduate and undergraduate) and post-docs from under-represented groups will be actively recruited by participating in institutional programs that reach out to minorities. Post-docs involved in the project will follow a career development plan supported by the research training in the lab, student mentoring experiences, and professional development training. Understanding the signal transduction pathways and the identification of important regulators of plant growth and development could positively impact food/feed/biofuel production, which is important to sustain the increasing world population.
Plants including all crop species come in different sizes and shapes, i.e. morphology. This is a result of differential regulations of growth and developmental processes in these different plants. Plant growth and development involve two key processes, cell differentiation and cell division. Cell differentiation gives rise to new cell types, and cell division increases the number of cells. In addition, the location and frequency of cell division i.e. stage-specific and localized cell division is also critical to the formation of normal tissues, organs, and organisms. The highly coordinated cell differentiation and proliferation events during growth and development illustrate the importance of cell-cell communication. In Arabidopsis, ERECTA (ER), a receptor-like kinase (RLK), and its paralogs, ER-like 1 (ERL1) and ERL2, play important roles in regulating localized cell proliferation, which influences both the architecture and the reproduction of plants. However, the downstream signaling components was unclear. During this award, we demonstrated that a complete mitogen-activated protein kinase (MAPK) cascade, composed of YDA, a MAPK kinase kinase (MAPKKK), MKK4 and MPK5, two functional redundant MAPK kinases (MAPKKs), and MPK3 and MPK6, two functional redundant MAPKs, functions downstream of ERECTA receptor to control the leaf petiole length, inflorescence stem length, and flower/fruit pedicel length in Arabidopsis. This MAPK cascade acts like a molecular switch in cells to control cell division in these organs, therefore, determining their sizes and shape i.e. their morphological appearance. Additional research was performed to figure out the molecular mechanism underlying the function of this MAPK cascade, including the substrate(s) of MPK3/MPK6, components/genes further downstream, and the involvement of auxin, a key plant hormone known to have an effect on plant cell division and differentiation. The results from this project have been published in five scientific journal articles, and additional results will be included in future manuscripts. The use of an integrative approach in this project provided an excellent training environment for students and post-docs. Several students, including one rotating graduate student, four undergraduate students, and two post-docs were involved in this project. Participation of undergraduate students in this research project sparked their interest in sciences and benefited the training of future generation of scientists. This project also allowed the training of a summer intern from a liberal art college as part of the MU Life Sciences Undergraduate Research Opportunity Program (LSUROP,www.lsurop.missouri.edu/). Hands-on research is an excellent way for students to learn the scientific method, and to collaborate with their peers. Engaging students by allowing them develop and carry out research projects not only helps them understand biological processes, but also develops their critical thinking skills. Studying the regulation of localized cell division is critical to our understanding of plant morphogenesis, which is related to many traits of the crop species. For instance, reducing the cell division along the length of the stem of a crop species will enhance its resistance to lodging. Increasing the cell division in the reproductive organ will increase the crop yield. Arabidopsis is a very useful model plants that allows us to study these basic scientific questions at a much-reduced cost. The knowledge learned could then be used in crop species to enhance their yield, which is important for agriculture to produce enough food/feed and harvestable energy to meet the increasing demand as world population increases.
