![]() The sugar signaling pathway and especially the well-known indicator of sucrose availability, trehalose-6-phosphate (T6P), were indicated to have a role in determining AXB fate in maize. In contrast, gibberellic acid (GA) biosynthesis and signaling were reduced in the tb1/ gt1 mutants, suggesting that the genes may promote AXB dormancy by downregulating the GA pathway. In this network, the phytohormonal signaling pathways of jasmonic acid (JA) and abscisic acid (ABA) promote bud dormancy, and are upregulated by TB1 both directly and indirectly via GT1. Using a combination of Chip-seq, RNA-seq, and metabolite measurements, recently showed that the three genes, namely TB1, gt1, and tru1, form a regulatory network in which TB1 is at the top of the hierarchy. The tru1 gene acts downstream of tb1, encodes an ankyrin-repeat domain protein with a BTB/POZ motif necessary for protein–protein interactions, and is directly activated by TB1. However, in some plant species, the role of apical dominance is not that strong and other factors regulate axillary bud (AXB) fate, as seen with the strawberry (see Section 2.4 on the regulation of the strawberry plant architecture). A change in the strength of apical dominance has major influences on plant form, as exemplified by the domestication of maize (see Section 2.1). The major endogenous signal regulating AXM fate is apical dominance, i.e., the inhibitory effect exerted by the SAM over AXMs (processes related to apical dominance are reviewed in Schneider et al. Depending on the plant species, the fates of different meristems are determined by endogenous or exogenous signals, or a mixture of both (reviewed in ). AXMs can develop into vegetative or generative branches, or remain dormant. SAMs can either keep on producing new vegetative plant tissues or, when induced to flower, differentiate into inflorescence meristems. The fates and relative growth rates of different meristems on the plant depend on both endogenous and exogenous factors, and determine the final form of plant architecture. The fundamental above-ground plant form is endogenously dictated at the shoot apical meristem (SAM), which gives rise to phyllotactic patterning, i.e., the arrangement of leaves (recently reviewed in ) each leaf is accompanied by an axillary meristem (AXM), located at leaf axil (for a review on AXM initiation, see, e.g., ). We also explain what is known about the genetic and environmental control of plant architecture in these species, and how further changes in plant architectural traits could benefit the horticultural sector. We focus specifically on the determination of the axillary meristem fate and review how plant architecture may change even drastically because of altered axillary meristem fate. In this review, we select a number of important horticultural and agricultural plant species as examples of how changes in plant architecture affect the cultivation practices of the species. Fortunately, research in many crop species has demonstrated that a relatively small number of genes has a large effect on axillary meristem fates. Knowledge of the genetic mechanisms regulating plant architecture is needed for precision breeding, especially for determining feasible breeding targets. Improving plant architecture by breeding facilitates denser plantations, better resource use efficiency and even mechanical harvesting. However, the fates of axillary meristems located in leaf axils have a great influence on plant architecture and affect the harvest index, yield potential and cultural practices. Shoot apical meristem gives rise to the fundamental plant form by generating new leaves. Above-ground plant architecture is dictated to a large extent by the fates and growth rates of aerial plant meristems. ![]()
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