Interactions of plant transcription factors regulate coordinated 3D patterning of grass leaves

About This Grant

Plant leaves perform vital photosynthetic functions, converting solar energy into sugars that empower all plant processes and directly impact crop yield. Leaves are multicellular organs that develop from meristematic, precursor stem cells, eventually forming complex, three-dimensional shapes that are critical for leaf function. Leaves of maize, a model plant for developmental research, comprise several grass-specific structures and features that maximize photosynthesis and provide structural support to the maize plant. This project will investigate the functional interactions of plant-specific genes with profound impacts on grass leaf development. The LIGULESS1 (LG1) gene functions to direct expression of other genes (i.e. transcription factors) that are involved in leaf width, length, and angle, with direct impacts on photosynthesis and leaf morphology. Three members of the WUSCHEL-related homeobox3 (WOX3) family of plant transcription factors are required to make leaves grow wide. Mutations in these wox3 genes give rise to short, mutant plants with leaves that fail to wrap-around and support the grass stems, which are thereby susceptible to lodging. Recent work has revealed that LG1 and WOX3 transcription factors interact during three-dimensional patterning of leaf angle and leaf wrapping. Genetic analyses of mosaic plants that have lost LG1 or WOX3 gene expression in specific plant regions during plant growth will reveal the timing, and cell/tissue/organ specificity of their respective functions. Candidate genes required for leaf-wrapping will be identified, and interactions between LG1 and WOX3 proteins will be analyzed in transgenic plants from a related grass, to better understand the mechanisms of grass leaf development. The PI will train undergraduate summer interns through a Research Experiences for Undergraduates (REU) program and provide training in state of the art molecular genetics research to a graduate student. The PI will teach a 3 credit science course for incarcerated students seeking an Associate Degree at a NY state penitentiary. A fundamental question in developmental biology is how growth and differentiation of lateral organs are coordinated along three-dimensions, comprising the dorsiventral, proximodistal, and mediolateral axes. Leaves arise from stem-cell pools called shoot apical meristems (SAMs) and are dorsiventrally-asymmetrical from their inception. Juxtaposition of dorsal and ventral domains organizes leaf-primordial outgrowth from the SAM along the mediolateral and proximodistal axes, creating a leaf that is tall, wide and flat. The maize leaf is an excellent model system for genetic, genomic, and cell-biological investigations of the mechanisms whereby axial development is spatially-regulated and coordinated. At maturity, the maize leaf is a strap-like structure with a distal, photosynthetic blade and a proximal sheath that wraps-around and supports the stem. Patterning of sheath wrapping is decidedly non-random in grasses. At the boundary between the blade and sheath, grass leaves develop a membranous outgrowth of epidermally-derived ligule, and a wedge-shaped auricle that function as a hinge to create leaf angle. Mutations in the grass transcription factor LIGULESS1 (LG1) remove the ligule and auricle, whereas mutations in WUSCHEL-related homeobox3 (WOX3) genes disrupt mediolateral leaf outgrowth and disrupt patterning of sheath margin wrapping. Higher-order wox3 and lg1 mutants reveal that LG1 and WOX3 transcription factors interact during proximo-distal and mediolateral patterning and leaf wrapping. Clonal sector analyses will reveal the ontogenetic timing, tissue-layer specificity, and cell-autonomy of LG1 and WOX3 function. State-of-the-art transcriptomics will identify candidate genes involved in sheath wrapping, and interactions of LG1 and WOX3 proteins will be examined in planta during ontogeny. 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.