Abstract
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.
Highlights
All post-embryonic plant tissues are derived from meristems, structures that harbor pluripotent stem cells
The genetic relationship and molecular function of FON1 and FON2 in rice are very similar to those of CLV1 and CLV3. These studies in both maize and rice suggest that the CLV pathway that negatively regulates stem cell maintenance is conserved in grasses
One of the first indications of the role of cytokinin in meristem maintenance came from the maize mutant aberrant phyllotaxy1, which has a defect in phyllotaxy and the geometric pattern of leaf initiation, and an enlarged meristem (Jackson and Hake 1999)
Summary
All post-embryonic plant tissues are derived from meristems, structures that harbor pluripotent stem cells. The genetic relationship and molecular function of FON1 and FON2 in rice are very similar to those of CLV1 and CLV3 These studies in both maize and rice suggest that the CLV pathway that negatively regulates stem cell maintenance is conserved in grasses. FCP1 and FOS1 probably act through a receptor other than FON1, because constitutive expression of either FCP1 or FOS1 shows a similar effect on shoot regeneration in the fon mutant to that observed in the wild type (Suzaki et al 2008, Suzaki et al 2009) These observations demonstrate that stem cell maintenance is likely to be regulated by at least three related negative pathways in rice, and each pathway seems to contribute differently to this regulation depending on the type of meristem
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