Grass meristems I: shoot apical meristem maintenance, axillary meristem determinacy and the floral transition.

The vegetative and reproductive shoot architectures displayed by members of the grass family are critical to reproductive success, and thus agronomic yield. Variation in shoot architecture is explained by the maintenance, activity and determinacy of meristems, pools of pluripotent stem cells responsible for post-embryonic plant growth. This review summarizes recent progress in understanding the major properties of grass shoot meristems, focusing on vegetative phase meristems and the floral transition, primarily in rice and maize. Major areas of interest include: the control of meristem homeostasis by the CLAVATA-WUSCHEL pathway and by hormones such as cytokinin; the initiation of axillary meristems and the control of axillary meristem dormancy; and the environmental and endogenous cues that regulate flowering time. In an accompanying paper, Tanaka et al. review subsequent stages of shoot development, including current knowledge of reproductive meristem determinacy and the fate transitions associated with these meristems.