Brassinosteroids regulate grain filling in rice

​The main interest of the group is the signal transduction pathway that plant cells use to respond to the growth promoting hormones, brassinosteroids. Brassinosteroids are ubiquitously distributed throughout the plant kingdom sterol derivatives. Brassinosteroid deficient mutants display dramatic developmental defects including dwarfism, male sterility, delayed flowering, reduced apical dominance, and a light-grown morphology when grown in dark. Like their animal counterparts, brassinosteroids regulate the expression of numerous genes, impact the activity of complex metabolic pathways, contribute to the regulation of cell division and differentiation, and help control overall development. Brassinosteroids regulate photomorphogenesis, etiolation and cell expansion. Brassinosteroids have a broad spectrum of activities that have a positive effect on the quantity and quality of crops and they increase plant resistance to stress and pathogens.

Brassinosteroid pathway is one of the best-defined signal transduction pathways in plants. In Arabidopsis , brassinosteroids are perceived by receptor kinases that transduce the signal from the cell surface to the nucleus by an intracellular cascade of phosphorylation mediated protein-protein interactions, involving kinases, phosphatases, 14-3-3 proteins, and nuclear transcription factors. In addition, the brassinosteroid signaling is regulated by the plant endocytic machinery because the increased endosomal localization of the brassinosteroid receptor enhances the signaling.

The main objective of the group is to combine genetic, molecular and cell biology tools to study mechanism of brassinosteroid signaling regulation in plants. One aspect of the research is to understand the subcellular compartmentalization and trafficking of brassinosteroid receptor complexes and their relevance to brassinosteroids physiological responses. We use chemical genomics and proteomics to investigate the subcellular localization, mobility, transport routes and binding interactions of different brassinosteroid signaling components. In addition we want to position important downstream brassinosteroid signaling regulators such as the Arabidopsis GSK3-like kinases in subcellular compartments important for brassinosteroid receptor activity.

The potential application of brassinosteroids in agriculture is based not only on their ability to increase crop yields but also on the fact that they increase resistance to different stress conditions such as high salinity, drought, fungal and viral infections. Thus, unraveling the regulatory mechanisms of brassinosteroid signaling on the level of signaling components, brassinosteroid target genes, endomembrane trafficking regulators or identifying chemicals that modulate any of those components can be used to develop selective strategies for high-yielding plants.

When GA binds to the GID1 receptor, it enhances the interaction between GID1 and DELLA proteins, forming a GA-GID1-DELLA complex. When in the GA-GID1-DELLA complex, it is thought that DELLA proteins undergo changes in structure that enable their binding to F-box protein s (SLY1 in arabidopsis or GID2 in rice). [52] [51] [53] F-box proteins catalyse the addition of ubiquitin to their targets [52] . The addition of ubiquitin to DELLA proteins promotes their degradation via the 26S-proteosome . [51] The degradation of DELLA proteins releases cells from their repressive effects.

A multiple sequence alignment of the CYP sequences revealed that CYP90E2 and CYP90F1 lack signal peptides that are required for targeting to the endoplasmic reticulum (ER) ( Figure 2A ). Thus, we postulated that these two proteins might function elsewhere in the cell. To test this idea, we predicted the subcellular localizations of these proteins using the PSORT program. CYP90E1 and CYP90E3 were found to localize to the ER with a score of above , where 1 indicates full certainty; however, CYP90E2 and CYP90F1 had a greater probability of localizing to the microbody (peroxisome) or cytoplasm than to the ER ( Figure 2B ). Some ER-targeted proteins are known to lack typical signal sequences [38] . Since cytochrome P450reductases (CPRs) catalyze the transfer of electrons from NAD(P)H to CYPs and therefore co-localize with the CYPs [39] , we would expect CPRs to co-localize with CYP90E2 and CYP90F1 at positions other than the ER.

Cytokinins have recently been found to play a role in plant pathogenesis. For example, cytokinins have been described to induce resistance against Pseudomonas syringae in Arabidopsis thaliana [14] and Nicotiana tabacum . [15] Also in context of biological control of plant diseases cytokinins seem to have potential functions. Production of cytokinins by Pseudomonas fluorescens G20-18 has been identified as a key determinant to efficiently control the infection of A. thaliana with P. syringae . [16]

Apical root growth requires iterative processes of cell division, elongation and differentiation. Root apical meristem localised at the root tip harbours stem cells that divide asymmetrically and generate initial cells for all the cell types in the root. Fates of these initial cells are determined by positional signals that integrate both intrinsic and extrinsic cues. The quiescent centre maintains the stem cells and thereby sustains a constant supply of cells for root growth. Another important aspect of root growth regulation is to balance the rate of cell division and differentiation. The crosstalks between plant hormones auxin and cytokinins help to establish this balance. Gene regulatory networks that govern root meristem activities and growth have been discovered over the years in the model plant Arabidopsis thaliana . This introductory article provides an overview of the organisation of the root meristem and the underlying regulatory mechanisms.

Brassinosteroids regulate grain filling in rice

brassinosteroids regulate grain filling in rice

Cytokinins have recently been found to play a role in plant pathogenesis. For example, cytokinins have been described to induce resistance against Pseudomonas syringae in Arabidopsis thaliana [14] and Nicotiana tabacum . [15] Also in context of biological control of plant diseases cytokinins seem to have potential functions. Production of cytokinins by Pseudomonas fluorescens G20-18 has been identified as a key determinant to efficiently control the infection of A. thaliana with P. syringae . [16]

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