Deformation of Root Cortex Cells during Rice Lateral Root Emergence: Examination of Cell Wall Remodeling during Development

Lateral roots (LR) represent the horizontal component of plant root systems and provide structural stability, increased nutrient uptake, and water absorption via extension of root system boundaries. In rice seedlings, LRs initiate through cellular division of the pericycle and must grow through or past several layers of extant tissues, including 3-5 cortex files, the schlerenchyma, the exodermis, and the epidermis. Comprehension of cell wall changes that occur during emergence and the regulation of this process might improve plant biomass deconstruction and lead to optimization of root architecture. This study seeks to characterize the cell wall and transcriptional changes in cells overlying the LR primordium. Propidium iodide (PI)-stained rice root tissue visualized with confocal light microscopy shows significant cell shape deformation, but not shearing, in cortex cells adjacent to the LR primordium. Preliminary data from immunofluorescence with primary antibodies targeting the cell wall matrix polysaccharides arabinoxylan and rhamnogalacturonan I suggest differences in cell wall composition between rice LR primordia and adjacent tissue in an 180^o forward arc near the primordia. Light microscopy images of LR will be utilized to generate a detailed 3D model of cell structure alterations toward understanding the timing of cellular changes during LR emergence. This information lays the groundwork for applying laser capture microdissection (LCM) to tissues overlying the primordia for transcriptome analysis. Changes in gene expression will provide insight into the regulatory cascades that control cell wall remodeling.