Abstract
Shoot branching is regulated by the complex interactions among hormones, development, and environ- mental factors. Recent studies into the regulatory mecha- nisms of shoot branching have focused on strigolactones, which is a new area of investigation in shoot branching regulation. Elucidation of the function of the D53 gene has allowed exploration of detailed mechanisms of action of strigolactones in regulating shoot branching. In addition, the recent discovery that sucrose is key for axillary bud release has challenged the established auxin theory, in which auxin is the principal agent in the control of apical dominance. These developments increase our understan- ding of branching control and indicate that regulation of shoot branching involves a complex network. Here, we first summarize advances in the systematic regulatory network of plant shoot branching based on current information. Then we describe recent developments in the synthesis and signal transduction of strigolactones. Based on these considerations, we further summarize the plant shoot branching regulatory network, including long distance systemic signals and local gene activity mediated by strigolactones following perception of external envi- ronmental signals, such as shading, in order to provide a comprehensive overview of plant shoot branching.
Highlights
1.1 Significance of plant shoot branchingBranching characteristics, including the number of lateral branches, their length and location on the stem, determine1.2 Stages of lateral branch developmentGenerally, plant lateral branch development consists of two phases: the initiation of meristems in the axil and elongation of the axillary bud[4]
These results indicated that auxin may function by regulating a signal that can move directly into the axillary buds by upregulating the expression of RMS1/ MAX4, a signal dependent on RMS1/MAX4 to inhibit shoot branching[37]
The study suggested that the localization of Petunia axillaries PLEIOTROPIC DRUG RESISTANCE 1 (PaPDR1) is determined by strigolactones and auxin. Another novel Nicotiana tabacum ATP binding cassette (ABC) transporter NtPDR6 was discovered in tobacco, which might function as a strigolactones transporter to regulate shoot branching[80] (Fig. 1)
Summary
Plant lateral branch development consists of two phases: the initiation of meristems in the axil and elongation of the axillary bud[4]. Axillary meristems are first initiated in axils, and form axillary buds. Buds either choose to continue in a dormant state or grow to form lateral branches. Axillary buds in dormancy can be activated into growth by the interaction between internal developmental signals and external environmental factors. The final number of branches depends on the number of axillary meristems and activity of the axillary buds. The plasticity of shoot branching depend on axillary buds activity (i.e., elongation of the axillary bud)[6]. We summarize the shoot branching regulatory network involved in long distance systemic signaling and local gene activity, mediated by strigolactones after plants receive external environment signals
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