Upstairs, Downstairs - conserved and divergent CLAVATA signalling in shoot meristem development and root symbioses.

Background: The CLV3/EMBRYO-SURROUNDING REGION (CLE) peptides control plant development and response to the environment. Key conserved roles include the regulation of shoot apical meristems and the long-distance control of root colonisation by nutrient-acquiring microbes, including the widespread symbioses with arbuscular mycorrhizal fungi and nodulation with nitrogen-fixing bacteria in legumes. At least some signalling elements appear to operate across both processes but clear gaps in our understanding remain.

Cell-layer specific roles for gibberellins in nodulation and root development.

Gibberellins (GA) have a profound influence on the formation of lateral root organs. However, the precise role this hormone plays in the cell-specific events during lateral root formation, rhizobial infection and nodule organogenesis, including interactions with auxin and cytokinin (CK), is not clear. We performed epidermal- and endodermal-specific complementation of the severely GA-deficient na pea (Pisum sativum) mutant with Agrobacterium rhizogenes.

The Role of CLE Peptides in the Suppression of Mycorrhizal Colonization of Tomato.

Symbioses with beneficial microbes are widespread in plants, but these relationships must balance the energy invested by the plants with the nutrients acquired. Symbiosis with arbuscular mycorrhizal (AM) fungi occurs throughout land plants, but our understanding of the genes and signals that regulate colonization levels is limited, especially in non-legumes. Here, we demonstrate that in tomato, two CLV3/EMBRYO-SURROUNDING REGION (CLE) peptides, SlCLE10 and SlCLE11, act to suppress AM colonization of roots.

Tangerine tomato roots show increased accumulation of acyclic carotenoids, less abscisic acid, drought sensitivity, and impaired endomycorrhizal colonization.

The Heirloom Golden tangerine tomato fruit variety is highly nutritious due to accumulation of tetra-cis-lycopene, that has a higher bioavailability and recognised health benefits in treating anti-inflammatory diseases compared to all-trans-lycopene isomers found in red tomatoes. We investigated if photoisomerization of tetra-cis-lycopene occurs in roots of the MicroTom tangerine (tang) tomato and how this affects root to shoot biomass, mycorrhizal colonization, abscisic acid accumulation, and responses to drought. tang plants grown in soil under glasshouse conditions displayed a reduction in height, number of flowers, fruit yield, and root length compared to wild-type (WT).

Right time, right place: The dynamic role of hormones in rhizobial infection and nodulation of legumes.

Many legume plants form beneficial associations with rhizobial bacteria that are hosted in new plant root organs, nodules, in which atmospheric nitrogen is fixed. This association requires the precise coordination of two separate programs, infection in the epidermis and nodule organogenesis in the cortex. There is extensive literature indicating key roles for plant hormones during nodulation, but a detailed analysis of the spatial and temporal roles of plant hormones during the different stages of nodulation is required.

Application of Strigolactones to Plant Roots to Influence Formation of Symbioses.

Strigolactones play a potent role in the rhizosphere as a signal to symbiotic microbes including arbuscular mycorrhizal fungi and rhizobial bacteria. This chapter outlines guidelines for application of strigolactones to pea roots to influence symbiotic relationships, and includes careful consideration of type of strigolactones applied, solvent use, frequency of application and nutrient regime to optimize experimental conditions.

The influence of ethylene, gibberellins and brassinosteroids on energy and nitrogen-fixation metabolites in nodule tissue.

Legume nodules are a unique plant organ that contain nitrogen-fixing rhizobial bacteria. For this interaction to be mutually beneficial, plant and bacterial metabolism must be precisely co-ordinated. Plant hormones are known to play essential roles during the establishment of legume-rhizobial symbioses but their role in subsequent nodule metabolism has not been explored in any depth.

The role of CLAVATA signalling in the negative regulation of mycorrhizal colonization and nitrogen response of tomato.

Plants form mutualistic nutrient-acquiring symbioses with microbes, including arbuscular mycorrhizal fungi. The formation of these symbioses is costly, and plants employ a negative feedback loop termed autoregulation of mycorrhizae (AOM) to limit formation of arbuscular mycorrhizae (AM). We provide evidence for the role of one leucine-rich repeat receptor-like kinase (FAB), a hydroxyproline O-arabinosyltransferase enzyme (FIN), and additional evidence for one receptor-like protein (SlCLV2) in the negative regulation of AM formation in tomato.

Brassinosteroids play multiple roles in nodulation of pea via interactions with ethylene and auxin.

A comprehensive analysis of the role of brassinosteroids in nodulation, including their interactions with auxin and ethylene revealed that brassinosteroids inhibit infection, promote nodule initiation but do not influence nodule organogenesis or function. Nodulation, the symbiosis between legumes and rhizobial bacteria, is regulated by a suite of hormones including brassinosteroids. Previous studies have found that brassinosteroids promote nodule number by inhibiting ethylene biosynthesis.

Overgrowth mutants determine the causal role of gibberellin GA2oxidaseA13 in Rht12 dwarfism of wheat.

The induced dwarf mutant Rht12 was previously shown to have agronomic potential to replace the conventional DELLA mutants Rht-B1b/Rht-D1b in wheat. The Rht12 dwarfing gene is not associated with reduced coleoptile length (unlike the DELLA mutants) and it is dominant, characteristics which are shared with the previously characterized dwarfing genes Rht18 and Rht14. Using the Rht18/Rht14 model, a gibberellin (GA) 2-oxidase gene was identified in the Rht12 region on chromosome 5A.

The role of CLV1, CLV2 and HPAT homologues in the nitrogen-regulation of root development.

Plants use a variety of signals to control root development, including in modifying root development in response to nutrient stress. For example, in response to nitrogen (N) stress, plants dramatically modulate root development, including the formation of N-fixing nodules in legumes. Recently, specific CLE peptides and/or receptors important for their perception, including CLV1 and CLV2, have been found to play roles in root development, including in response to N supply.

What drives interspecies graft union success? Exploring the role of phylogenetic relatedness and stem anatomy.

The underlying mechanisms that determine whether two species can form a successful graft union (graft compatibility) remain obscure. Two prominent hypotheses are (1) the more closely related species are, the higher the graft success and (2) the vascular anatomy at the graft junction influences graft success. In this paper these two hypotheses are examined in a systematic way using graft combinations selected from a range of (a) phylogenetically close and more distant legume species, (b) species displaying different germination patterns and (c) scions and rootstocks possessing contrasting stem tissues and vascular patterns.

The DELLA Proteins Influence the Expression of Cytokinin Biosynthesis and Response Genes During Nodulation.

The key event that initiates nodule organogenesis is the perception of bacterial signal molecules, the Nod factors, triggering a complex of responses in epidermal and cortical cells of the root. The Nod factor signaling pathway interacts with plant hormones, including cytokinins and gibberellins. Activation of cytokinin signaling through the homeodomain-containing transcription factors KNOX is essential for nodule formation.

The Role of Gibberellins and Brassinosteroids in Nodulation and Arbuscular Mycorrhizal Associations.

Plant hormones play key roles in nodulation and arbuscular mycorrhizal (AM) associations. These two agriculturally and ecologically important symbioses enable plants to gain access to nutrients, in particular, nitrogen in the case of nodulation and phosphorous in the case of AM. Work over the past few decades has revealed how symbioses with nitrogen-fixing rhizobia, restricted almost exclusively to legumes, evolved in part from ancient AM symbioses formed by more than 80% of land plants.

Auxin transport and stem vascular reconnection - has our thinking become canalized?

Background: The presence of a polar auxin transport stream has long been correlated with the differentiation and patterning of vascular cells across vascular plants. As our understanding of auxin transport and vascular development has grown, so too has evidence for the correlation between these processes. However, a clear understanding of the cellular and molecular mechanisms driving this correlation has not been elucidated.

The Art of Self-Control - Autoregulation of Plant-Microbe Symbioses.

Plants interact with diverse microbes including those that result in nutrient-acquiring symbioses. In order to balance the energy cost with the benefit gained, plants employ a systemic negative feedback loop to control the formation of these symbioses. This is particularly well-understood in nodulation, the symbiosis between legumes and nitrogen-fixing rhizobia, and is known as autoregulation of nodulation (AON).

Semidwarfism in Wheat Is Due to Increased Expression and Reduced GA Content.

Semidwarfing genes have improved crop yield by reducing height, improving lodging resistance, and allowing plants to allocate more assimilates to grain growth. In wheat (), the semidwarfing gene was identified and deployed in durum wheat before it was transferred into bread wheat, where it was shown to have agronomic potential. , a dominant and gibberellin (GA) responsive mutant, is genetically and functionally distinct from the widely used GA-insensitive semidwarfing genes and In this study, the gene was identified by mutagenizing the semidwarf durum cultivar Icaro () and generating mutants with a range of tall phenotypes.

Gibberellins promote nodule organogenesis but inhibit the infection stages of nodulation.

Leguminous plant roots can form a symbiosis with soil-dwelling nitrogen-fixing rhizobia, leading to the formation of a new root organ, the nodule. Successful nodulation requires co-ordination of spatially separated events in the root, including infection in the root epidermis and nodule organogenesis deep in the root cortex. We show that the hormone gibberellin plays distinct roles in these epidermal and cortical programmes.

Cytokinins and the CRE1 receptor influence endogenous gibberellin levels in Medicago truncatula.

Gibberellins (GAs) and cytokinins (CKs) are hormones that play antagonistic roles in several developmental processes in plants. However, there has been little exploration of their reciprocal interactions. Recent work in Medicago truncatula has revealed that GA signalling can regulate CK levels and response in roots.

Determining the Site of Action of Strigolactones during Nodulation.

Strigolactones (SLs) influence the ability of legumes to associate with nitrogen-fixing bacteria. In this study, we determine the precise stage at which SLs influence nodulation. We show that SLs promote infection thread formation, as a null SL-deficient pea () mutant forms significantly fewer infection threads than wild-type plants, and this reduction can be overcome by the application of the synthetic SL GR24.

Strigolactones in Plant Interactions with Beneficial and Detrimental Organisms: The Yin and Yang.

Strigolactones (SLs) are plant hormones that have important roles as modulators of plant development. They were originally described as ex planta signaling molecules in the rhizosphere that induce the germination of parasitic plants, a role that was later linked to encouraging the beneficial symbiosis with arbuscular mycorrhizal (AM) fungi. Recently, the focus has shifted to examining the role of SLs in plant-microbe interactions, and has revealed roles for SLs in the association of legumes with nitrogen-fixing rhizobacteria and in interactions with disease-causing pathogens.

Farnesylation mediates brassinosteroid biosynthesis to regulate abscisic acid responses.

Protein farnesylation is a post-translational modification involving the addition of a 15-carbon farnesyl isoprenoid to the carboxy terminus of select proteins(1-3). Although the roles of this lipid modification are clear in both fungal and animal signalling, many of the mechanistic functions of farnesylation in plant signalling are still unknown. Here, we show that CYP85A2, the cytochrome P450 enzyme that performs the last step in brassinosteroid biosynthesis (conversion of castasterone to brassinolide)(4), must be farnesylated to function in Arabidopsis.

Interactions between ethylene, gibberellins, and brassinosteroids in the development of rhizobial and mycorrhizal symbioses of pea.

The regulation of arbuscular mycorrhizal development and nodulation involves complex interactions between the plant and its microbial symbionts. In this study, we use the recently identified ethylene-insensitive ein2 mutant in pea (Pisum sativum L.) to explore the role of ethylene in the development of these symbioses.

The role of strigolactones during plant interactions with the pathogenic fungus Fusarium oxysporum.

Strigolactones (SLs) do not influence spore germination or hyphal growth of Fusarium oxysporum. Mutant studies revealed no role for SLs but a role for ethylene signalling in defence against this pathogen in pea. Strigolactones (SLs) play important roles both inside the plant as a hormone and outside the plant as a rhizosphere signal in interactions with mycorrhizal fungi and parasitic weeds.