A carotenoid-derived hormonal signal that inhibits shoot branching in plants has long escaped identification. Strigolactones are compounds thought to be derived from carotenoids and are known to trigger the germination of parasitic plant seeds and stimulate symbiotic fungi. Here we present evidence that carotenoid cleavage dioxygenase 8 shoot branching mutants of pea are strigolactone deficient and that strigolactone application restores the wild-type branching phenotype to ccd8 mutants. Moreover, we show that other branching mutants previously characterized as lacking a response to the branching inhibition signal also lack strigolactone response, and are not deficient in strigolactones. These responses are conserved in Arabidopsis. In agreement with the expected properties of the hormonal signal, exogenous strigolactone can be transported in shoots and act at low concentrations. We suggest that endogenous strigolactones or related compounds inhibit shoot branching in plants. Furthermore, ccd8 mutants demonstrate the diverse effects of strigolactones in shoot branching, mycorrhizal symbiosis and parasitic weed interaction.

Strigolactone inhibition of shoot branching

Shoot branching is a major determinant of plant architecture and is highly regulated by endogenous and environmental cues. Two classes of hormones, auxin and cytokinin, have long been known to have an important involvement in controlling shoot branching. Previous studies using a series of mutants with enhanced shoot branching suggested the existence of a third class of hormone(s) that is derived from carotenoids, but its chemical identity has been unknown. Here we show that levels of strigolactones, a group of terpenoid lactones, are significantly reduced in some of the branching mutants. Furthermore, application of strigolactones inhibits shoot branching in these mutants. Strigolactones were previously found in root exudates acting as communication chemicals with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Thus, we propose that strigolactones act as a new hormone class-or their biosynthetic precursors-in regulating above-ground plant architecture, and also have a function in underground communication with other neighbouring organisms.

Inhibition of shoot branching by new terpenoid plant hormones

Vascular plants appeared ~410 million years ago, then diverged into several lineages of which only two survive: the euphyllophytes (ferns and seed plants) and the lycophytes. We report here the genome sequence of the lycophyte Selaginella moellendorffii (Selaginella), the first nonseed vascular plant genome reported. By comparing gene content in evolutionarily diverse taxa, we found that the transition from a gametophyte- to a sporophyte-dominated life cycle required far fewer new genes than the transition from a nonseed vascular to a flowering plant, whereas secondary metabolic genes expanded extensively and in parallel in the lycophyte and angiosperm lineages. Selaginella differs in posttranscriptional gene regulation, including small RNA regulation of repetitive elements, an absence of the trans-acting small interfering RNA pathway, and extensive RNA editing of organellar genes.

https://science.sciencemag.org/content/sci/332/6032/960.full.pdf

The Selaginella genome identifies genetic changes associated with the evolution of vascular plants.

Carotenoids and tocopherols are the two most abundant groups of lipid-soluble antioxidants in chloroplasts. In addition to their many functional roles in photosynthetic organisms, these compounds are also essential components of animal diets, including humans. During the past decade, a near complete set of genes required for the synthesis of both classes of compounds in photosynthetic tissues has been identified, primarily as a result of molecular genetic and biochemical genomics-based approaches in the model organisms Arabidopsis thaliana and Synechocystis sp. PCC6803. Mutant analysis and transgenic studies in these and other systems have provided important insight into the regulation, activities, integration, and evolution of individual enzymes and are already providing a knowledge base for breeding and transgenic approaches to modify the types and levels of these important compounds in agricultural crops.

Vitamin synthesis in plants: tocopherols and carotenoids.

Shoot branching patterns depend on a key developmental decision: whether axillary buds grow out to give a branch or whether they remain dormant in the axils of leaves. This decision is controlled by endogenous and environmental stimuli mediated by hormonal signals. Although genes involved in the long-distance signaling of this process have been identified, the genes responding inside the buds to cause growth arrest remained unknown in Arabidopsis thaliana. Here, we describe an Arabidopsis gene encoding a TCP transcription factor closely related to teosinte branched1 (tb1) from maize (Zea mays), BRANCHED1 (BRC1), which represents a key point at which signals controlling branching are integrated within axillary buds. BRC1 is expressed in developing buds, where it arrests bud development. BRC1 downregulation leads to branch outgrowth. BRC1 responds to developmental and environmental stimuli controlling branching and mediates the response to these stimuli. Mutant and expression analyses suggest that BRC1 is downstream of the MORE AXILLARY GROWTH pathway and that it is required for auxin-induced apical dominance. Therefore, BRC1 acts inside the buds as an integrator of signals controlling bud outgrowth and translates them into a response of cell growth arrest. The conservation of BRC1/tb1 function among distantly related angiosperm species suggests that a single ancestral mechanism of branching control integration evolved before the radiation of flowering plants.

/pdf/arabidopsis-branched1-acts-as-an-integrator-of-branching-1xx4jn8egr.pdf

Arabidopsis BRANCHED1 Acts as an Integrator of Branching Signals within Axillary Buds

https://www.cell.com/developmental-cell/pdf/S1534-5807(05)00013-4.pdf

MAX1 encodes a cytochrome P450 family member that acts downstream of MAX3/4 to produce a carotenoid-derived branch-inhibiting hormone

The overall input of nitrogen into global agriculture for food and feed production is estimated to be approximately 120 million tonnes/yr. Biological nitrogen fixation (BNF) accounts for 40 million tonnes/yr and 80 million tonnes/yr is accounted for by N-fertiliser production from ammonia. In cereal production fertiliser use dominates. If cereals were able to fix their own nitrogen the situation could be very different. However, this is unlikely to be realised in the near future unless the technological complexities of inducing BNF in non-legume crops can be overcome. Traditionally, work in this area has tended to focus on the transfer of legume-like BNF characteristics to non-legumes and so far commercially, this strategy has not been successful. More promising may be work that has purported to show that some species of endophytic bacteria living within non-legumes (e.g. grasses) can supply nitrogen to their host plants. The potential of this approach is discussed here based upon current experience with the use of bacterial inoculants for legume production (in particular Soya production). The relative merits of N-inoculants and N-fertilisers are discussed along with issues that are relevant for the future development of BNF in non-legumes as seen from an industrial perspective. Many of the current environmental concerns about the use of mineral fertilisers can also be applied to the use of N-inoculants. It is concluded that if N-inoculants for non-legume crops are developed then these will have to be at least as convenient, safe, reliable and effective in growing crop for an ever-increasing global population as N-fertilisers are today.

Review article What can be Learnt From the Current Use of Inoculants in Legume Production? The Relative Merits of Mineral Fertilisers and N-Inoculants

What can be learnt from the current use of inoculants in legume production? The relative merits of mineral fertilisers and N-inoculants

A fusion protein comprising: a cellulose binding domain peptide; and a cell surface polypeptide. The cell surface polypeptide is capable of causing the cellulose binding domain peptide to be exposed on the surface of a cell. The present invention also relates to a nucleic acid encoding the fusion protein and a vector that includes the nucleic acid. In addition, the present invention relates to a cell transformed with the nucleic acid and to a method of increasing cellular adhesion of cells. Furthermore, the present invention relates to a method of improving plant growth or health.

A fusion protein comprising a cellulose binding domain

A fusion protein comprising: a cellulose binding domain peptide; and a cell surface polypeptide. The cell surface polypeptide is capable of causing the cellulose binding domain peptide to be exposed on the surface of a cell.

A fusion protein

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