Inflorescence abscission zones in grasses: Diversity and genetic regulation

Abscission of the fruit and associated floral structures, also called shattering, is a crucial survival strategy for propagation of wild grasses, and the loss of shattering in cereal crops is one of the most important domestication traits. Abscission occurs in specialised cell layers called the abscission zone (AZ). The fruit and floral AZs in different grass species are morphologically and anatomically diverse. In this article, we take a comparative approach and summarise our knowledge of the AZs in grasses at morphological, anatomical, and genetic levels.We show that the AZs in different grass species differ in terms of the position along the inflorescence, cell shapes of the AZ, and cell wall properties in the AZ, indicating distinctive mechanisms of abscission in these species. We further review the progress in illuminating the genetic regulation of AZ development in a few cereal crops. Current data suggest both conserved regulatorymolecular mechanisms within grasses and between grass and dicot models, as well as unique gene functions currently found only in certain grass species. The rapid growth of genomic sequencing and molecular technologies will further advance our understanding of the molecular regulatory network and evolution of the AZ development.