Programmed Cell Death in Developing Brachypodium distachyon Grain

Abstract

O_LIThe normal developmental sequence in a grass grain entails the death of several maternal and filial tissues in a genetically regulated process termed programmed cell death (PCD). The progression and molecular aspects of PCD in developing grain have been reported for domesticated species like barley, rice, maize and wheat. Here, we report a detailed investigation of PCD in the developing grain of a wild model species, Brachypodium distachyon.\nC_LIO_LIWe detected PCD in developing Brachypodium grains using molecular and histological approaches. We also identified and surveyed the expression of Brachypodium orthologs of protease genes known to contribute to grain PCD.\nC_LIO_LIWe found that Brachypodium nucellus degenerates by PCD in a centrifugal pattern following anthesis, although at a slower rate compared to cultivated cereals. Mesocarp PCD was not coordinated with endosperm development. Brachypodium lacks an expansion of vacuolar processing enzymes known for their roles in nucellar PCD.\nC_LIO_LICombined with existing knowledge on grain PCD, our study suggests the importance of rapid nucellar PCD for grain size and that the pattern of mesocarp PCD affects grain shape.\nC_LI