Auxin, cytokinin and the control of shoot branching
TL;DR: It has been known for many decades that auxin inhibits the activation of axillary buds, and hence shoot branching, while cytokinin has the opposite effect as mentioned in this paper. But the modes of action of these two hormones in branching control is still a matter of debate, and their mechanisms of interaction are equally unresolved.
About: This article is published in Annals of Botany.The article was published on 2011-05-01 and is currently open access. It has received 404 citations till now. The article focuses on the topics: Auxin & Cytokinin.
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TL;DR: Within a higher plant, strigolactones appear to be involved in controlling the balance of resource distribution via strategic modification of growth and development, which changes root growth and promotes fungal symbiosis to enhance phosphate intake.
306 citations
TL;DR: The complex nature of plant stress signaling network is discussed, with a specific attention to ROS as the primary source of the signaling battery in plants and the interaction between ROS and other signaling components, e.g., redox homeostasis, MAPKs, and plant hormones has been assessed.
251 citations
TL;DR: Current knowledge on the function of auxin and cytokinin in redirecting growth induced by abiotic stress is reviewed in order to deduce their potential points of crosstalk.
Abstract: Plant growth and development are critically influenced by unpredictable abiotic factors. To survive fluctuating changes in their environments, plants have had to develop robust adaptive mechanisms. The dynamic and complementary actions of the auxin and cytokinin pathways regulate a plethora of developmental processes, and their ability to crosstalk makes them ideal candidates for mediating stress-adaptation responses. Other crucial signaling molecules responsible for the tremendous plasticity observed in plant morphology and in response to abiotic stress are reactive oxygen species (ROS). Proper temporal and spatial distribution of ROS and hormone gradients is crucial for plant survival in response to unfavorable environments. In this regard, the convergence of ROS with phytohormone pathways acts as an integrator of external and developmental signals into systemic responses organized to adapt plants to their environments. Auxin and cytokinin signaling pathways have been studied extensively. Nevertheless, we do not yet understand the impact on plant stress tolerance of the sophisticated crosstalk between the two hormones. Here, we review current knowledge on the function of auxin and cytokinin in redirecting growth induced by abiotic stress in order to deduce their potential points of crosstalk.
209 citations
TL;DR: Transcriptional profiling of shade-treated wild-type and brc1 axillary buds of plants treated with simulated shade revealed a group of ABA response genes and a network of cell cycle– and ribosome-related genes whose mRNA levels are dependent on BRC1 function, which may play a key role in the growth-to-dormancy transition in buds.
Abstract: Plants interpret a decrease in the red to far-red light ratio (R:FR) as a sign of impending shading by neighboring vegetation. This triggers a set of developmental responses known as shade avoidance syndrome. One of these responses is reduced branching through suppression of axillary bud outgrowth. The Arabidopsis thaliana gene BRANCHED1 (BRC1), expressed in axillary buds, is required for branch suppression in response to shade. Unlike wild-type plants, brc1 mutants develop several branches after a shade treatment. BRC1 transcription is positively regulated 4 h after exposure to low R:FR. Consistently, BRC1 is negatively regulated by phytochrome B. Transcriptional profiling of wild-type and brc1 buds of plants treated with simulated shade has revealed groups of genes whose mRNA levels are dependent on BRC1, among them a set of upregulated abscisic acid response genes and two networks of cell cycle– and ribosome-related downregulated genes. The downregulated genes have promoters enriched in TEOSINTE BRANCHED1, CYCLOIDEA, and PCF (TCP) binding sites, suggesting that they could be transcriptionally regulated by TCP factors. Some of these genes respond to BRC1 in seedlings and buds, supporting their close relationship with BRC1 activity. This response may allow the rapid adaptation of plants to fluctuations in the ratio of R:FR light.
199 citations
TL;DR: This work has highlighted that auxin export from a bud is important for its subsequent growth, and perception of the recently discovered hormone strigolactone is now quite well understood, while the downstream targets remain largely unknown.
186 citations
References
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TL;DR: This work shows that five PIN genes collectively control auxin distribution to regulate cell division and cell expansion in the primary root and reveals an interaction network of auxin transport facilitators and root fate determinants that control patterning and growth of the root primordium.
Abstract: Local accumulation of the plant growth regulator auxin mediates pattern formation in Arabidopsis roots and influences outgrowth and development of lateral root- and shoot-derived primordia. However, it has remained unclear how auxin can simultaneously regulate patterning and organ outgrowth and how its distribution is stabilized in a primordium-specific manner. Here we show that five PIN genes collectively control auxin distribution to regulate cell division and cell expansion in the primary root. Furthermore, the joint action of these genes has an important role in pattern formation by focusing the auxin maximum and restricting the expression domain of PLETHORA (PLT) genes, major determinants for root stem cell specification. In turn, PLT genes are required for PIN gene transcription to stabilize the auxin maximum at the distal root tip. Our data reveal an interaction network of auxin transport facilitators and root fate determinants that control patterning and growth of the root primordium.
1,794 citations
TL;DR: The results are consistent with the hypothesis that cytokinins have central, but opposite, regulatory functions in root and shoot meristems and indicate that a fine-tuned control of catabolism plays an important role in ensuring the proper regulation of cytokinin functions.
Abstract: Cytokinins are hormones that regulate cell division and development. As a result of a lack of specific mutants and biochemical tools, it has not been possible to study the consequences of cytokinin deficiency. Cytokinin-deficient plants are expected to yield information about processes in which cytokinins are limiting and that, therefore, they might regulate. We have engineered transgenic Arabidopsis plants that overexpress individually six different members of the cytokinin oxidase/dehydrogenase (AtCKX) gene family and have undertaken a detailed phenotypic analysis. Transgenic plants had increased cytokinin breakdown (30 to 45% of wild-type cytokinin content) and reduced expression of the cytokinin reporter gene ARR5:GUS (beta-glucuronidase). Cytokinin deficiency resulted in diminished activity of the vegetative and floral shoot apical meristems and leaf primordia, indicating an absolute requirement for the hormone. By contrast, cytokinins are negative regulators of root growth and lateral root formation. We show that the increased growth of the primary root is linked to an enhanced meristematic cell number, suggesting that cytokinins control the exit of cells from the root meristem. Different AtCKX-green fluorescent protein fusion proteins were localized to the vacuoles or the endoplasmic reticulum and possibly to the extracellular space, indicating that subcellular compartmentation plays an important role in cytokinin biology. Analyses of promoter:GUS fusion genes showed differential expression of AtCKX genes during plant development, the activity being confined predominantly to zones of active growth. Our results are consistent with the hypothesis that cytokinins have central, but opposite, regulatory functions in root and shoot meristems and indicate that a fine-tuned control of catabolism plays an important role in ensuring the proper regulation of cytokinin functions.
1,365 citations
TL;DR: The cloned teosinte branched1 (tb1) gene encodes a protein with homology to the cycloidea gene of snapdragon and suggests that tb1 acts both to repress the growth of axillary organs and to enable the formation of female inflorescences.
Abstract: The domestication of crop plants has often involved an increase in apical dominance (the concentration of resources in the main stem of the plant and a corresponding suppression of axillary branches). A striking example of this phenomenon is seen in maize (Zea mays spp. mays), which exhibits a profound increase in apical dominance compared with its probable wild ancestor, teosinte (Zea mays ssp. parviglumis). Previous research has identified the teosinte branched1 (tb1) gene as a major contributor to this evolutionary change in maize. We have cloned tb1 by transposon tagging and show here that it encodes a protein with homology to the cycloidea gene of snapdragon. The pattern of tb1 expression and the morphology of tb1 mutant plants suggest that tb1 acts both to repress the growth of axillary organs and to enable the formation of female inflorescences. The maize allele of tb1 is expressed at twice the level of the teosinte allele, suggesting that gene regulatory changes underlie the evolutionary divergence of maize from teosinte.
1,316 citations
TL;DR: Results from tryptophan analog feeding experiments and biochemical assays indicate that YUCCA catalyzes hydroxylation of the amino group of tryptamine, a rate-limiting step in tryptophile-dependent auxin biosynthesis.
Abstract: Although auxin is known to regulate many processes in plant development and has been studied for over a century, the mechanisms whereby plants produce it have remained elusive. Here we report the characterization of a dominant Arabidopsis mutant, yucca, which contains elevated levels of free auxin. YUCCA encodes a flavin monooxygenase-like enzyme and belongs to a family that includes at least nine other homologous Arabidopsis genes, a subset of which appears to have redundant functions. Results from tryptophan analog feeding experiments and biochemical assays indicate that YUCCA catalyzes hydroxylation of the amino group of tryptamine, a rate-limiting step in tryptophan-dependent auxin biosynthesis.
1,089 citations
TL;DR: These results provide new insight into auxin transport dynamics during primordial positioning and suggest a role for Auxin transport in influencing primordial cell type.
1,064 citations