Ultimately, all of the world’s food supply, as well as many other crucial products, depend on energy harvested from sunlight by plants. This sunlight is captured by leaves that have shapes optimized for light harvesting while minimizing water loss. Leaves of some plants are also adapted to growing in extreme environments such as high stress or high salt conditions, showing that there are genetic controls of growth responses to the environment. Understanding how leaves adapt to the environment through cell growth will provide foundational information for a resilient and sustainable agriculture in the face of changing environments. Leaves generally grow by increasing cell number through division followed by an increase in cell size by expansion. It is not clear how these two processes of division and expansion are controlled to give rise to the final shape of a leaf. This research explores the function of a family of regulators that restrict cell division and promote the switch to cell expansion in the genetic model plant Arabidopsis thaliana. The findings are then applied to study how cell expansion is controlled in response to salt exposure in leaves of the salt-adapted plant Schrenkiella parvula. Understanding how plants can grow in extreme salt-stressed conditions will provide basic information about how plants respond and adapt to the environment. The next generation of scientists will be trained in hands-on research through experience in the laboratory and by developing course-based undergraduate research projects in plant biology.
The SIAMESE-RELATED (SMR) family of cyclin-dependent kinase inhibitors, first discovered in the Larkin lab, are key regulators of the transition from cell proliferation to endoreplication, an alternate version of the cell cycle in which DNA replication continues without subsequent division. Two family members, SMR1 and SMR2, have distinct effects on leaf cell number, cell size and overall leaf size in Arabidopsis thaliana. Our central hypothesis is that SMRs serve as key regulators of leaf growth for both developmental and environmental cues by controlling the timing and extent of endoreplication during leaf development. This hypothesis will be tested by examining the regulation and functional roles of the SMR1 and SMR2 genes during leaf development, and by examining the role of SMRs in Schrenkiella parvula leaf development in response to salt treatment. This work will contribute to the identification of regulatory networks controlling the onset of endoreplication in leaves, and to understanding the role of endoreplication in leaf function and stress adaptation, and will develop resources for the extremophyte model S. parvula. The proposed work will play a role in the education of three graduate students and several undergraduates from a wide diversity of backgrounds. A course-based undergraduate research experience (CURE) lab focusing on gene expression is also planned, using SMR promoter:reporter fusion transgenic lines that will be produced as part of the proposed research.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
