The shoot apical meristem (SAM) is responsible for development of all above ground organs in the plant. SAM structure and function correlates with agronomically-important adult traits in the maize plant, and is also affected by planting density and shade stresses induced by agricultural environments. The ultimate goal of this project is to increase understanding of the regulatory networks controlling SAM structure and function and the responses of these networks to environmental stresses. The specific objectives are to: 1) describe the SAM allometric space in maize and its relatives using nanoscale computer tomographic scanning to provide 3-dimensional images of the phenotypic diversity of SAM structure and identify adult plant traits correlated with SAM structure; 2) identify differentially expressed genes in SAM size/shape outliers and mutants with abnormal SAM structures and generate a co-expression network of key genes implicated during SAM structure and function; 3) perform quantitative genetic analyses to identify specific variations within genes that correlate with variations in SAM structure/function and adult plant traits, and test functions of 40 key genes using reverse genetic aaproaches; 4) analyze the shade avoidance response and its effects on SAM structure and function; and 5) investigate epigenetic changes of SAM functional domains in response to shade avoidance using novel protocols that distinguish the stem cell organizing regions from the organogenic domains in the maize SAM.
These studies will provide the framework for scientific training and the public release of original data. Undergraduates at Truman State University, a small liberal arts institution, will be trained in morphological and LM-RNAseq analyses of maize mutants. REU students and undergraduates enrolled in Plant Physiology courses at Cornell University will participate in physiological experiments. This project will generate extensive transcriptomic data and vector constructs for tissue-specific epigenetic analyses which will be available to the scientific research community. Molecular markers and phenotypic data for diverse maize lines will be supplied to Panzea. Genetic mapping associations, physiological shade-avoidance response data, transcriptomic and phenotypic data will be curated at MaizeGDB, and seed stocks for maize shoot mutants and SAM size variants will be released through the Maize Genetics Cooperation Stock Center.