Control of plant architecture
A striking feature of plants is the huge variety of plant forms that can be found in nature. This enormous diversity is due to variation in the shape, size, proportion and relative position of the different organs in the aerial part of the plant. Evolutionary changes in the three-dimensional organization, or architecture, of plant shoots have played a central role in the morphological diversification of plant species. Moreover, plant architecture is a determining factor in the agronomic performance of crop plants. Most plant architecture traits can be directly retraced to changes in activity and/or size of the shoot apical meristem (SAM) and derived meristems, such as lateral or axillary meristems (AMs) and floral meristems (FMs). The activity of these meristems is determined both by the plant’s genetic program and by environmental factors. Our work focuses on unraveling corresponding signaling pathways involved in controlling shoot meristem activity. Plant processes that have our special attention are floral timing and bolting.
The role of TALE homeodomain proteins in floral evocation and internode elongation
Plant members of the TALE (three-amino acid loop extension)-superclass of homeodomain (HD) transcription factor (TF) proteins play essential roles in the regulation of various aspects of plant architecture, including shoot apical meristem (SAM) maintenance, leaf size, leaf shape, leaf number, phyllotaxy, floral transition, plant height, internode patterning, and floral specification. In plants, the TALE HD protein class comprises two subfamilies: the BELL (BEL1-like) class and the Knotted1-like homeobox (KNOX) class. BELL proteins associate with KNOX proteins to form heterodimers to compose functional complexes that regulate plant development. A common feature of KNOX-BELL interactions is that the KNOX protein partner often interacts with a subset of BELL proteins and vice versa. Different combinations have both unique and overlapping targets. Our work focuses on unraveling BELL-KNOX regulatory networks (TF protein-protein interactions and their respective downstream targets) involved in the vegetative to generative phase transition and the bolting process that is normally accompanied with it. Functional analysis of the Arabidopsis family of BELL-class TALE homeobox genes, revealed that three of its members, ATH1, PNY and PNF have both overlapping and antagonistic functions in these processes. All three proteins interact with class I KNOX proteins. These interactions are a prerequisite for proper cellular localization and, thus, functioning of the corresponding TALE HD heterodimeric complexes. Current research focuses on the combinatorial mapping of primary targets of selected BELL-KNOX heterodimers to obtain essential information on the molecular processes that contribute to establishment of above-ground plant architecture.
Control of floral evocation by environmental stimuli
Timing of flowering depends on environmental conditions and internal signals from the plant’s genetic program to induce flowering in plants at the most favorable conditions for reproductions to enhance fitness. In Arabidopsis thaliana most studies have focused on for the plant highly predictable factors involved in flowering, like day length (photoperiod) and extended periods of cold (vernalization). However, less predictable factors, including ambient temperature (15-30°C) are equally important. In general, plants flower earlier at higher temperatures. This is accompanied by increased elongation responses. In this project we aim to unravel the molecular mechanisms underlying temperature-mediated flowering and elongation responses by means of, among others, natural variation studies.
Metabolic control of meristem activity
Plant growth and development critically depend on carbon nutrient status. Processes that especially require significant energy input are phase transitions and the initiation and outgrowth of new shoot organs, such as floral transition and lateral branches/flowers, respectively. These processes are of vital importance to plant productivity and have major impact on reproductive output and thereby yield in many crops. Most of these traits are directly linked to changes in activity and/or size of shoot apical meristems, including axillary and floral meristems. Previous research points to the importance of carbon nutrients controlling meristem activity for plant growth, development, and yield, but no systematic analyses of the mechanisms involved have been performed. We are currently using combined natural variation and transcriptome analyses to identify loci/genes that coordinate shoot apical meristem activity changes according to the sugar availability and energy status of the plant.