The SELF-PRUNING gene of tomato regulates vegetative to reproductive switching of sympodial meristems and is the ortholog of CEN and TFL1

LEAF DEVELOPMENT IN ANGIOSPERMS

Leaves are produced in succession on the shoot apical meristem (SAM) of a plant. The three landmark stages in leaf morphogenesis include initiation, acquisition of suborgan identities, and tissue differentiation. The expression of various genes relative to these steps in leaf morphogenesis is described. KNOTTED-like homeobox (KNOX) genes, FLO/LFY, and floral homeotic genes may be involved in generation of leaf shape and complexity. The differences between compound leaves and simple leaves in gene expression characteristics and morphogenetic patterns are discussed.

Separation of shoot and floral identity in Arabidopsis

The overall morphology of an Arabidopsis plant depends on the behaviour of its meristems. Meristems derived from the shoot apex can develop into either shoots or flowers. The distinction between these alternative fates requires separation between the function of floral meristem identity genes and the function of an antagonistic group of genes, which includes TERMINAL FLOWER 1. We show that the activities of these genes are restricted to separate domains of the shoot apex by different mechanisms. Meristem identity genes, such as LEAFY, APETALA 1 and CAULIFLOWER, prevent TERMINAL FLOWER 1 transcription in floral meristems on the apex periphery. TERMINAL FLOWER 1, in turn, can inhibit the activity of meristem identity genes at the centre of the shoot apex in two ways; first by delaying their upregulation, and second, by preventing the meristem from responding to LEAFY or APETALA 1. We suggest that the wild-type pattern of TERMINAL FLOWER 1 and floral meristem identity gene expression depends on the relative timing of their upregulation.

Genetic control of branching in Arabidopsis and tomato

The patterns of axillary bud formation and the growth characteristics of side-shoots determine to a large extent the form of plants. Characterization of mutants in the monopodial plant Arabidopsis thaliana and in the sympodial tomato, as well as cloning of some of the respective genes, contributes to a better understanding of side-shoot development. Genes have been identified that influence the initiation of axillary meristems and the pattern of their subsequent development.

The making of a flower: control of floral meristem identity in IT>Arabidopsis/IT>

During the reproductive phase of a plant, shoot meristems follow one of two developmental programs to produce either flowers or vegetative shoots. The decision as to which meristems give rise to flowers, and when they do so, determines the general morphology of an inflorescence. Molecular and genetic research in Arabidopsis and other model species has identified several genes that control the identity that a meristem will adopt. These meristem identity genes are activated in response to developmental and environmental cues, and can be assigned to three basic categories: those required either to initiate or maintain the floral program in some meristems and those required to maintain the vegetative program in others.