Increased pod shattering of Caragana species adapted to arid environments

Pod shattering, in which mature pods split along their dorsal and ventral sutures, has been widely reported in legume crops due to yield losses. However, the pod-shattering behavior of native legumes that have adapted to decreasing precipitation remains poorly understood. In this study, pod-shattering rates, histology, pod wall components, hydrolase activity and transcriptome of the pod ventral sutures were measured in six Caragana species adapted to a wide range of mean annual precipitation (MAP) conditions and growing in a common garden. Species from low-MAP environments presented higher pod-shattering rates, which were associated with a more pronounced abscission zone (AZ), more pod wall torsion laps, lower contents of cellulose and pectin, and increased activities and gene expression levels of polygalacturonase (PG) and cellulase (CE). In contrast, species from high-MAP environments presented lower pod-shattering rates, which were associated with the absence of an AZ, lower pod wall torsion laps, higher cellulose and pectin contents, and reduced activities and gene expression levels of PG and CE. This study hypothesizes that pod-shattering synchronizes seed release to match rainfall patterns, offering a new perspective for understanding the natural distribution of legumes adapted to arid environments.