**1. Introduction**

Transcription factors (TFs), also known as trans-acting factors, are proteins with special structures that regulate plant growth and development. Transcription factors bind to specific DNA sequences (cis-acting elements) in the upstream promoter region of target genes through their DNA-binding domain (DBD), thereby regulating the specific expression of target genes in different cell types of plants or under different environmental conditions [1]. In plant morphogenesis, selective expression of genes leads to the differentiation of phenotypes, and transcription factors play an important regulatory role in these processes. TFs are divided into different gene families, such as the bHLH, TCP, MADS, bZIP, KNOX, WOX, AP2/ERF, NAC, GATA and ARF families, according to differences in DNA-binding domains and conserved motifs.

Shoot branching is a common phenomenon in plant growth and plays a very important role in plant morphogenesis. Branching also affects plant competitiveness against weeds or pests [2,3]. Therefore, research on branching mechanisms has become a popular topic worldwide. Studies have shown that axillary meristems initiate from cell groups detached from the primary SAM that retain their meristematic identity (Figure 1). Alternatively, axillary meristems may originate de novo later in development from partially or fully differentiated cells. Development of the lateral branch involves two important processes, axillary meristem formation and axillary bud growth [4,5].

**Citation:** Zhang, L.; Fang, W.; Chen, F.; Song, A. The Role of Transcription Factors in the Regulation of Plant Shoot Branching. *Plants* **2022**, *11*, 1997. https://doi.org/10.3390/ plants11151997

Academic Editor: Giovanna Frugis

Received: 7 July 2022 Accepted: 29 July 2022 Published: 31 July 2022

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**Figure 1.** Steps of plant shoot branching. (**a**) indicates the axillary meristem at the leaf primordium axils. (**b**) indicates the formation of axillary meristems (area shown in yellow box in (**a**)). (**c**) represents the development of plant axillary meristem into young branches.

Through a study on the regulatory mechanism of plant branching, a series of branchingrelated transcription factors (Table 1) have been isolated from *Oryza sativa*, *Arabidopsis thaliana*, *Lycopersicon esculentum*, *Zea mays* and other plants. However, the nomenclature of homologous genes in different species is confusing, and related studies on transcription factors involved in the regulation of branching development are lacking in systematic elaboration. Branch formation is regulated at two developmental stages: axillary bud meristem formation and axillary bud emergence. The latter is induced by bud dormancy release and regulated by the synergistic effect of plant hormones such as auxin (IAA), strigolactones (SLs), cytokinins (CKs), abscisic acid (ABA) and brassinosteroids (BRs) [6,7]. Of course, many endogenous and developmental signals can be integrated to determine the fate of buds and the number and location of new buds growing on plants. This regulation is also strongly dependent on environmental factors, and plants adjust their branching ability according to their environmental conditions [8].


**Table 1.** Transcription factors involved in regulating plant branching.

*Plants* **2022**, *11*, 1997


#### **Table 1.** *Cont.*


**Table 1.** *Cont.*

Note: The transcription factor prefix indicates the species to which it belongs. At—Arabidopsis thaliana; Os— Oryza sativa; Ha—Helianthus annuus; Cr—Ceratopteris richardii; Zm—Zea mays; Sl—Solanum lycopersicum; Md—Malus pumila; Vv—Vitis vinifera.

In this review, we begin with the formation and growth of axillary meristems to elaborate on the research progress of transcription factors involved in regulating plant branching development to provide target genes for manipulating plant branching.
