Abstract text: Plants anchor to soil and acquire water and nutrients through root branching. Lateral root initiation and emergence occur under the biomechanical constraints of overlying tissue layers, which shrink or separate to make way for the newly growing organ. Pectic homogalacturonan in the cell wall and middle lamella can be degraded by polygalacturonases (PGs) that function in developmental processes requiring cell elongation and/or separation. Expression analyses in Arabidopsis thaliana point to endo-PGs, which cleave the middle of homogalacturonan chains, functioning in lateral root development. However, how pectin degradation by different PGs enables lateral root emergence is poorly understood. We found that an insertional mutant of an exo-PG that degrades pectin from chain ends shows a reduction in lateral root density and a delay in lateral root emergence. We hypothesize that this PG plays a unique role in the separation of overlying tissue to facilitate lateral root emergence. Using confocal microscopy on roots immunolabeled for different forms of pectin, we are currently analyzing the spatiotemporal dynamics of PG activity at the cellular level. With this work we aim to address the longstanding question of how PGs with specific biochemical properties and cellular dynamics conduct the development and outgrowth of an organ.