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At least 19 recordsLinked to original sources
PubMed2004

Shoot branching.

The mature form of a plant shoot system is an expression of several genetically controlled traits, many of which are also environmentally regulated. A major component of this architectural variation is the degree of shoot branching. Recent results indicate conserved mechanisms for shoot branch development across the monocots and eudicots. The existence of a novel long-range branch-inhibiting signal has been inferred from studies of branching mutants in pea and Arabidopsis.

Arabidopsis↗
PubMed2003

MAX4 and RMS1 are orthologous dioxygenase-like genes that regulate shoot branching in Arabidopsis and pea.

Shoot branching is inhibited by auxin transported down the stem from the shoot apex. Auxin does not accumulate in inhibited buds and so must act indirectly. We show that mutations in the MAX4 gene of Arabidopsis result in increased and auxin-resistant bud growth. Increased branching in max4 shoots is restored to wild type by grafting to wild-type rootstocks, suggesting that MAX4 is required to produce a mobile branch-inhibiting signal, acting downstream of auxin. A similar role has been proposed for the pea gene, RMS1. Accordingly, MAX4 and RMS1 were found to encode orthologous, auxin-inducible members of the polyene dioxygenase family.

Arabidopsis↗
PubMed2003

Regulation of shoot branching by auxin.

The idea that apically derived auxin inhibits shoot branching by inhibiting the activity of axillary buds was first proposed 70 years ago, but it soon became clear that its mechanism of action was complex and indirect. Recent advances in the study of axillary bud development and of auxin signal transduction are allowing a better understanding of the role of auxin in controlling shoot branching. These studies have identified a new role for auxin early in bud development as well as some of the second messengers involved in mediating the branch-inhibiting effects of auxin.

Gene Expression Regulation, Developmental↗
PubMed2006

The Arabidopsis MAX pathway controls shoot branching by regulating auxin transport.

BACKGROUND: Plants achieve remarkable plasticity in shoot system architecture by regulating the activity of secondary shoot meristems, laid down in the axil of each leaf. Axillary meristem activity, and hence shoot branching, is regulated by a network of interacting hormonal signals that move through the plant. Among these, auxin, moving down the plant in the main stem, indirectly inhibits axillary bud outgrowth, and an as yet undefined hormone, the synthesis of which in Arabidopsis requires MAX1, MAX3, and MAX4, moves up the plant and also inhibits shoot branching. Since the axillary buds of max4 mutants are resistant to the inhibitory effects of apically supplied auxin, auxin and the MAX-dependent hormone must interact to inhibit branching. RESULTS: Here we show that the resistance of max mutant buds to apically supplied auxin is largely independent of the known, AXR1-mediated, auxin signal transduction pathway. Instead, it is caused by increased capacity for auxin transport in max primary stems, which show increased expression of PIN auxin efflux facilitators. The max phenotype is dependent on PIN1 activity, but it is independent of flavonoids, which are known regulators of PIN-dependent auxin transport. CONCLUSIONS: The MAX-dependent hormone is a novel regulator of auxin transport. Modulation of auxin transport in the stem is sufficient to regulate bud outgrowth, independent of AXR1-mediated auxin signaling. We therefore propose an additional mechanism for long-range signaling by auxin in which bud growth is regulated by competition between auxin sources for auxin transport capacity in the primary stem.

Arabidopsis↗
PubMed2006

AtMBD9: a protein with a methyl-CpG-binding domain regulates flowering time and shoot branching in Arabidopsis.

The functional characterization of mammalian proteins containing a methyl-CpG-binding domain (MBD) has revealed that MBD proteins can decipher the epigenetic information encoded by DNA methylation, and integrate DNA methylation, modification of chromatin structure and repression of gene expression. The Arabidopsis genome has 13 putative genes encoding MBD proteins, and no specific biological function has been defined for any AtMBD genes. In this study, we identified three T-DNA insertion mutant alleles at the AtMBD9 locus, and found that all of them exhibited obvious developmental abnormalities. First, the atmbd9 mutants flowered significantly earlier than wild-type plants. The expression of FLOWERING LOCUS C (FLC), a major repressor of Arabidopsis flowering, was markedly attenuated by the AtMBD9 mutations. This FLC transcription reduction was associated with a significant decrease in the acetylation level in histone H3 and H4 of FLC chromatin in the atmbd9 mutants. Secondly, the atmbd9 mutants produced more shoot branches by increasing the outgrowth of axillary buds when compared with wild-type plants. The two known major factors controlling the outgrowth of axillary buds in Arabidopsis, auxin and the more axillary growth (MAX) pathway, were found not to be involved in producing this enhanced shoot branching phenotype in atmbd9 mutants, indicating that AtMBD9 may regulate a novel pathway to control shoot branching. This pathway is not related to FLC expression as over-expression of FLC in atmbd9-2 restored its flowering time to one similar to that of the wild type, but did not alter the shoot branching phenotype.

Arabidopsis↗
PubMed2005

Shoot branching.

All plant shoots can be described as a series of developmental modules termed phytomers, which are produced from shoot apical meristems. A phytomer generally consists of a leaf, a stem segment, and a secondary shoot meristem. The fate and activity adopted by these secondary, axillary shoot meristems is the major source of evolutionary and environmental diversity in shoot system architecture. Axillary meristem fate and activity are regulated by the interplay of genetic programs with the environment. Recent results show that these inputs are channeled through interacting hormonal and transcription factor regulatory networks. Comparison of the factors involved in regulating the function of diverse axillary meristem types both within and between species is gradually revealing a pattern in which a common basic program has been modified to produce a range of axillary meristem types.

Meristem↗
PubMed2003

LAX and SPA: major regulators of shoot branching in rice.

The aerial architecture of plants is determined primarily by the pattern of shoot branching. Although shoot apical meristem initiation during embryogenesis has been extensively studied by molecular genetic approaches using Arabidopsis, little is known about the genetic mechanisms controlling axillary meristem initiation, mainly because of the insufficient number of mutants that specifically alter it. We identified the LAX PANICLE (LAX) and SMALL PANICLE (SPA) genes as the main regulators of axillary meristem formation in rice. LAX encodes a basic helix-loop-helix transcription factor and is expressed in the boundary between the shoot apical meristem and the region of new meristem formation. This pattern of LAX expression was repeatedly observed in every axillary meristem, consistent with our observation that LAX is involved in the formation of all types of axillary meristems throughout the ontogeny of a rice plant. Ectopic LAX expression in rice caused pleiotropic effects, including dwarfing, an altered pattern of stem elongation, darker color, bending of the lamina joint, absence of the midribs of leaves, and severe sterility.

Amino Acid Sequence↗
PubMed2005

Hormonally controlled expression of the Arabidopsis MAX4 shoot branching regulatory gene.

The Arabidopsis MORE AXILLARY BRANCHING 4 (MAX4) gene is required for the production of a long-range, graft-transmissible signal that inhibits shoot branching. Buds of max4 mutant plants are resistant to the inhibitory effects of apically applied auxin, indicating that MAX4 is required for auxin-mediated bud inhibition. The RAMOSUS 1 (RMS1) and DECREASED APICAL DOMINANCE 1 (DAD1) genes of pea and petunia, respectively, are orthologous to MAX4 and function in a similar way. Here we show that, despite the similarities between these three genes, there are significant differences in the regulation of their expression. RMS1 is known to be upregulated by auxin in the shoot, suggesting a straightforward link between the RMS1-dependent branch-inhibiting signal and auxin, whereas we find that MAX4 is only upregulated by auxin in the root and hypocotyl, and this is not required for the inhibition of shoot branching. Furthermore, both RMS1 and DAD1 are subject to feedback regulation, for which there is no evidence for MAX4. Instead, overexpression studies and reciprocal grafting experiments demonstrate that the most functionally significant point of interaction between auxin and MAX4 is post-transcriptional and indeed post-synthesis of the MAX4-dependent graft-transmissible signal.

Arabidopsis↗
PubMed2000

Measuring and modeling conductances of black spruce at three organizational scales: shoot, branch and canopy.

To investigate the extent to which the energy balance of a globally important ecosystem is controlled by biological and environmental processes, measurements of water vapor flux were made on individual black spruce (Picea mariana [Mill.] B.S.P.) shoots, branches, and a whole canopy at the BOREAS Southern Study Area Old Black Spruce (SSA OBS) site. These measurements were used to estimate stomatal, branch boundary layer and canopy boundary layer conductances to water vapor. On a projected needle area basis, stomatal conductances varied between 14 and 92 mmol m(-2) s(-1), and total branch conductance varied seasonally between zero and about 35 mmol m(-2) s(-1). On a ground area basis, total canopy conductance varied between 24 and 105 mmol m(-2) s(-1). Total canopy conductance was partitioned into aerodynamic and physiological components by using shoot-scale measurements scaled by leaf area index. Good agreement was found with an independent estimate of aerodynamic conductance measured when the canopy was wet. Compared with most coniferous forests, the canopy was relatively uncoupled from the atmosphere, and at the ecosystem scale, the control of water vapor flux was approximately equally divided between physiological and abiotic conductances. Two widely used steady-state models of stomatal conductance were parameterized from the shoot and branch measurements. Parameters varied considerably throughout the growing season. A time-constant term was added to these static models to construct dynamic models of stomatal conductance under naturally varying environmental conditions. The dynamic versions of the models outperformed the static versions in explaining stomatal response to rapidly changing environmental conditions. The length of the time-constant term, derived using the dynamic models, suggested that stomata were slow to respond to changing environmental conditions, and that the speed of the response was strongly temperature-dependent.

Journal Article↗
PubMed2002

Photosynthesis and respiration of black spruce at three organizational scales: shoot, branch and canopy.

To gain insight into the function of photosynthesis and respiration as processes operating within a global ecosystem, we measured gas exchange of mature black spruce (Picea mariana (Mill.) B.S.P.) trees at three organizational scales: individual shoots, whole branches and a forest canopy. A biochemical model was fitted to these data, and physiological parameters were extracted. Pronounced seasonal variation in the estimated model parameters was found at all three organizational scales, highlighting the need to make physiological measurements throughout the year. For example, it took over 100 days for physiological activity to increase from zero during the springtime thaw to its yearly maximum. Good agreement was found between parameter values estimated for the different organizational scales, suggesting that, in the case of aerodynamically rough, largely mono-specific forest canopies, physiological parameters can be estimated from eddy covariance flux measurements. The small differences between photosynthetic parameters estimated at the different scales suggest that the overall spatial organization of photosynthetic capacity is nearly optimized for carbon uptake at each scale.

Carbon Dioxide↗
PubMed1999

AXR1 acts after lateral bud formation to inhibit lateral bud growth in Arabidopsis.

The AXR1 gene of Arabidopsis is required for many auxin responses. The highly branched shoot phenotype of mature axr1 mutant plants has been taken as genetic evidence for a role of auxin in the control of shoot branching. We compared the development of lateral shoots in wild-type Columbia and axr1-12 plants. In the wild type, the pattern of lateral shoot development depends on the developmental stage of the plant. During prolonged vegetative growth, axillary shoots arise and develop in a basal-apical sequence. After floral transition, axillary shoots arise rapidly along the primary shoot axis and grow out to form lateral inflorescences in an apical-basal sequence. For both patterns, the axr1 mutation does not affect the timing of axillary meristem formation; however, subsequent lateral shoot development proceeds more rapidly in axr1 plants. The outgrowth of lateral inflorescences from excised cauline nodes of wild-type plants is inhibited by apical auxin. axr1-12 nodes are resistant to this inhibition. These results provide evidence for common control of axillary growth in both patterns, and suggest a role for auxin during the late stages of axillary shoot development following the formation of the axillary bud and several axillary leaf primordia.

Arabidopsis↗
PubMed2002

MAX1 and MAX2 control shoot lateral branching in Arabidopsis.

Plant shoots elaborate their adult form by selective control over the growth of both their primary shoot apical meristem and their axillary shoot meristems. We describe recessive mutations at two loci in Arabidopsis, MAX1 and MAX2, that affect the selective repression of axillary shoots. All the first order (but not higher order) axillary shoots initiated by mutant plants remain active, resulting in bushier shoots than those of wild type. In vegetative plants where axillary shoots develop in a basal to apical sequence, the mutations do not clearly alter node distance, from the shoot apex, at which axillary shoot meristems initiate but shorten the distance at which the first axillary leaf primordium is produced by the axillary shoot meristem. A small number of mutant axillary shoot meristems is enlarged and, later in development, a low proportion of mutant lateral shoots is fasciated. Together, this suggests that MAX1 and MAX2 do not control the timing of axillary meristem initiation but repress primordia formation by the axillary meristem. In addition to shoot branching, mutations at both loci affect leaf shape. The mutations at MAX2 cause increased hypocotyl and petiole elongation in light-grown seedlings. Positional cloning identifies MAX2 as a member of the F-box leucine-rich repeat family of proteins. MAX2 is identical to ORE9, a proposed regulator of leaf senescence ( Woo, H. R., Chung, K. M., Park, J.-H., Oh, S. A., Ahn, T., Hong, S. H., Jang, S. K. and Nam, H. G. (2001) Plant Cell 13, 1779-1790). Our results suggest that selective repression of axillary shoots involves ubiquitin-mediated degradation of as yet unidentified proteins that activate axillary growth.

Amino Acid Sequence↗
PubMed2001

Atmospheric carbon dioxide concentration, nitrogen availability, temperature and the photosynthetic capacity of current-year Norway spruce shoots.

Branches of field-grown Norway spruce (Picea abies (L.) Karst.) trees were exposed to either long-term ambient or to elevated CO2 concentrations ([CO2]) using the branch bag technique. The light-saturated photosynthetic rates (A(max)) of current-year shoots differing in nitrogen (N) status were measured at various temperatures and at either ambient (360 micromol mol(-1), AMB) or elevated (ambient + 350 micromol mol(-1), EL) [CO2]. The value of A(max) was determined at various intercellular [CO2]s (A/Ci curves) and used to normalize photosynthetic rates to the mean treatment C(i) values, which were 200 micromol mol(-1) (AMB) and 450 micromol mol(-1) (EL), respectively. Needle N status and temperature strongly affected A(max). The response to N increased with temperature, and the photosynthetic temperature optimum increased with N status. This was assumed to be a result of reduced mesophyll CO2 conductance. The relative increase of Amax in the EL treatment compared to the AMB treatment varied from 15 to 90%, and increased with temperature, but decreased with N status. Nevertheless, the absolute photosynthetic response to EL increased with shoot N status. The relative increase in the instantaneous response of A(max) to elevated [CO2] was about 20% higher than the long-term response, i.e., there was downward acclimation in Amax in response to elevated [CO2]. The photosynthetic temperature optimum increased 4 degrees C with either a short- or a long-term increase in [CO2]. The bag treatment itself increased A(max) by approximately 16% and the temperature optimum of A(max) by approximately 3 degrees C.

Carbon Dioxide↗
PubMed2005

The branching gene RAMOSUS1 mediates interactions among two novel signals and auxin in pea.

In Pisum sativum, the RAMOSUS genes RMS1, RMS2, and RMS5 regulate shoot branching via physiologically defined mobile signals. RMS1 is most likely a carotenoid cleavage enzyme and acts with RMS5 to control levels of an as yet unidentified mobile branching inhibitor required for auxin inhibition of branching. Our work provides molecular, genetic, and physiological evidence that RMS1 plays a central role in a shoot-to-root-to-shoot feedback system that regulates shoot branching in pea. Indole-3-acetic acid (IAA) positively regulates RMS1 transcript level, a potentially important mechanism for regulation of shoot branching by IAA. In addition, RMS1 transcript levels are dramatically elevated in rms3, rms4, and rms5 plants, which do not contain elevated IAA levels. This degree of upregulation of RMS1 expression cannot be achieved in wild-type plants by exogenous IAA application. Grafting studies indicate that an IAA-independent mobile feedback signal contributes to the elevated RMS1 transcript levels in rms4 plants. Therefore, the long-distance signaling network controlling branching in pea involves IAA, the RMS1 inhibitor, and an IAA-independent feedback signal. Consistent with physiological studies that predict an interaction between RMS2 and RMS1, rms2 mutations appear to disrupt this IAA-independent regulation of RMS1 expression.

Alleles↗
PubMed2004

MAX3/CCD7 is a carotenoid cleavage dioxygenase required for the synthesis of a novel plant signaling molecule.

BACKGROUND: Plant development is exquisitely environmentally sensitive, with plant hormones acting as long-range signals that integrate developmental, genetic, and environmental inputs to regulate development. A good example of this is in the control of shoot branching, where wide variation in plant form can be generated in a single genotype in response to environmental and developmental cues. RESULTS: Here we present evidence for a novel plant signaling molecule involved in the regulation of shoot branching. We show that the MAX3 gene of Arabidopsis is required for the production of a graft-transmissible, highly active branch inhibitor that is distinct from any of the previously characterized branch-inhibiting hormones. Consistent with its proposed function in the synthesis of a novel signaling molecule, we show that MAX3 encodes a plastidic dioxygenase that can cleave multiple carotenoids. CONCLUSIONS: We conclude that MAX3 is required for the synthesis of a novel carotenoid-derived long-range signal that regulates shoot branching.

Abscisic Acid↗
PubMed2006

The origin, initiation and development of axillary shoot meristems in Lotus japonicus.

BACKGROUND AND AIMS: Lotus japonicus 'Gifu' develops multiple axillary shoots in the cotyledonary node region throughout the growth of the plant. The origin, initiation and development of these axillary meristems were investigated. METHODS: Morphological, histological and mRNA in situ analyses were done to characterize the ontogeny of cotyledonary axillary shoot meristems in Lotus. Morphological characterization of a putative Lotus shoot branching mutant (super-accessory branches) sac, is presented. KEY RESULTS: By using expression of an L. japonicus STM-like gene as a marker for meristematic tissues, it was demonstrated that groups of cells maintained in the meristematic state at the cotyledonary axil region coincide with the sites where additional axillary meristems (accessory meristems) form. A Lotus shoot branching mutant, sac, is a putative Lotus branching mutant characterized by increased proliferation of accessory shoots in all leaf axils including the cotyledons. CONCLUSION: In Lotus, axillary shoot meristems continually develop at the cotyledonary node region throughout the growth of the plant. These cotyledonary primary and accessory axillaries arise from the position of a meristematic zone of tissue at the cotyledonary node axil region.

Amino Acid Sequence↗