Shoot branching
Introduction
Changes in plant architecture have been central to the domestication of wild species; for example, the ‘Green Revolution’ saw the introduction of wheat varieties that had modified architecture that increased yield and improved resistance to wind and rain damage [1]. The architecture of the shoot system affects a plant’s light-harvesting potential, the synchrony of flowering and seed set, and ultimately the reproductive success a plant. Flowering plants display a remarkable range of inflorescence architectures, which are defined by the degree of branching, internodal elongation and shoot determinancy. In this review, we discuss only the role of axillary meristems in influencing shoot architecture.
Shoot branches arise from axillary shoot meristems, which form in the axils of leaves on the primary shoot axis. After initiation, axillary meristems produce a few leaves to form a bud. At this stage, the bud may either develop as a vegetative branch immediately or remain dormant indefinitely until outgrowth is triggered. Hence, the degree of branching depends not only on the establishment of an axillary meristem but also upon its subsequent activity. In this review, we focus on recent studies that illustrate the importance of auxin, cytokinin and an as yet unidentified substance in regulating axillary meristem activity. We also discuss the genetic regulation of axillary meristem initiation, highlighting recent studies that have identified common components from eudicots and monocots.
Section snippets
Axillary meristem initiation
Mutants that have altered patterns of shoot branching have been described in several species, including tomato, pea, maize and Arabidopsis. They fall into three classes on the basis of whether they affect meristem initiation (e.g. revoluta, pinhead, lateral suppressor [ls] and blind/torosa), meristem outgrowth (e.g. more axillary growth [max], ramosus [rms] and decreased apical dominance [dad]) or both (e.g. supershoot/bushy and Teosinte branched1 [Tb1]) [2]. In this section, we highlight the
Axillary meristem activity
During vegetative development in Arabidopsis, axillary meristems are initiated and released in an acropetal gradient at a distance from the SAM. The converse is true following floral transition, when axillary meristems are released in a basipetal sequence in close proximity to the SAM 14., 15.. Arabidopsis has a monopodial growth habit, which is characterised by the SAM’s remaining active throughout the life span of the plant. In other species, such as tomato and Petunia, a sympodial growth
Site of auxin action
The weight of evidence shows that auxin does not act directly in the bud to inhibit outgrowth. It must, therefore, act elsewhere to control the synthesis, transport or metabolism of one or more second messengers. Two sites for auxin action have been proposed in two recent studies. First, auxin resistant1 (axr1) mutations result in increased shoot branching [21]. The axr1-12 mutation promotes the growth of axillary buds. Analysis of the response of axr1-12 buds to apically applied auxin in
Second messengers for auxin action
In addition to several potential sites of action for auxin, there are several proposed second messengers that could relay the auxin signal into the bud. Each of these is also likely to have auxin-independent roles in regulating bud growth. The possible role of cytokinin has already been mentioned above. It is clear that cytokinin can promote bud outgrowth; for example, the application of basal cytokinin can overcome the effects of apical auxin in the Arabidopsis excised node assay [19].
Conclusions
This review focusses on recent developments in understanding the control of shoot branching. Two major themes are apparent. First, it is clear that the use of a range of different approaches and techniques offers the best opportunity for progress. Grafting techniques and classical physiological approaches have been successfully combined with molecular genetic and transgenic approaches. This trend will no doubt continue with the addition of high-throughput genomics approaches, which have already
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
- •
of special interest
- ••
of outstanding interest
Acknowledgements
We would like to acknowledge funding from the Biotechnology and Biological Sciences Research Council (BBSRC) of the UK. We thank members of the Leyser lab for critical reading of the manuscript and helpful discussions.
References (40)
- et al.
Seed and fruit set of the lateral suppressor mutant of tomato
Sci Hortic (Amsterdam)
(1994) - et al.
Control of tillering in rice
Nature
(2003) - Klee HJ, Lanahan MB: Transgenic plants in plant biology. In Plant Hormones: Physiology, Biochemistry and Molecular...
- et al.
‘Green revolution’ genes encode mutant gibberellin response modulators
Nature
(1999) - et al.
Control of outgrowth and dormancy in axillary buds
Plant Physiol
(2001) - et al.
The Lateral suppressor (Ls) gene of tomato encodes a new member of the VHIID protein family
Proc Natl Acad Sci USA
(1999) - et al.
Molecular analysis of the LATERAL SUPPRESSOR gene in Arabidopsis reveals a conserved control mechanism for axillary meristem formation
Genes Dev
(2003) - et al.
Initiation of axillary and floral meristems in Arabidopsis
Dev Biol
(2000) - et al.
The evolution of apical dominance in maize
Nature
(1997) - et al.
DNA binding and dimerization specificity and potential targets for the TCP protein family
Plant J
(2002)
Expression patterns and mutant phenotype of teosinte branched1 correlate with growth suppression in maize and teosinte
Genetics
The OsTB1 gene negatively regulates lateral branching in rice
Plant J
Origin of floral asymmetry in Antirrhinum
Nature
The TCP domain: a motif found in proteins regulating plant growth and development
Plant J
Bi-directional inflorescence development in Arabidopsis thaliana: acropetal initiation of flowers and basipetal initiation of paraclades
Planta
An altered body plan is conferred on Arabidopsis plants carrying dominant alleles of two genes
Development
Genetic control of branching in Arabidopsis and tomato
Curr Opin Plant Biol
Studies on the growth hormone of plants. III. The inhibiting action of the growth substance on bud development
Proc Natl Acad Sci USA
Hormonal regulation of bud growth in Arabidopsis
Plant J
Cited by (107)
Effect of the mode and time of gibberellic acid treatment on plant architecture and bulb structure in garlic (Allium sativum L.)
2019, Scientia HorticulturaeCitation Excerpt :Hence, soluble sugar significantly decreased during axillary bud release (at 32 days after GA3 treatment). Meanwhile, soluble protein also participated in the process of axillary bud outgrowth (Ward and Leyser, 2004). Axillary meristem formation and bud growth result in an increase in soluble protein (Lv et al., 2017), which is similar to our results.
PzTAC and PzLAZY from a narrow-crown poplar contribute to regulation of branch angles
2017, Plant Physiology and BiochemistryCitation Excerpt :In recent years, researchers have paid much attention to plant architecture, from analysis of its structure to elucidation of regulatory molecular mechanisms, in herbaceous crops and fruit trees (Wang and Li, 2005; Schneider et al., 2012). Many factors, such as leaf dimensions, internodal elongation, and branch angle, influence plant architecture (Ward and Leyser, 2004; Dardick et al., 2013). Branch angle has been examined in diverse tree species (Wilson, 2000; Dardick et al., 2013).
Identification of candidate genes for dissecting complex branch number trait in chickpea
2016, Plant ScienceCitation Excerpt :Branching exerts its impact on dry matter accumulation and assimilates partitioning into the vegetative compartment and the reproductive growth [3]. Branching also affects developmental phenotypes, including flowering time and reproductive success in plant [4]. The process of axillary shoot branch formation is controlled by a complex interaction between genetically regulated developmental process and the environment [5,6].
Progress of research on hormone regulation of branching or tillering in plants
2024, Acta Prataculturae SinicaRice husk-derived biogenic silica nanoparticles and zinc oxide nanoparticles as nano-additives for improving in vitro quince rootstock propagation
2023, Plant Cell, Tissue and Organ Culture