The role of SMXL7 in plant vessel formation

• Applicant: Professor Dr. Thomas Greb
• Subject Area: Plant Cell and Developmental Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541639494

Continuous growth and tissue formation are characteristic for plant development and important for aligning distinct body structures with changing environmental conditions. Cambium-driven radial growth of shoots and roots of dicotyledonous species is an important feature of this growth mode, and key for biomass production and for the long-term sequestration of CO2. Cambium stem cells (CSCs) proliferate usually providing wood (i.e. xylem) cells inwards and bast (i.e. phloem) cells outwards. Within xylem and phloem tissues, various cell types fulfil highly specialized functions like water transport by xylem vessel elements or sugar transport by phloem sieve elements. However, mechanisms regulating CSC-associated cell fate decisions to cope with stressful environmental conditions are largely unknown. Here, we propose to tackle this gap of knowledge in the context of a PhD project by identifying gene targets of the strigolactone (SL) signaling pathway regulating vessel element formation. We recently uncovered the impact of the SL signaling pathway on the formation of vessel elements in Arabidopsis thaliana. The central observations are that plants in which the SL pathway is impaired, density and size of vessel elements within radially growing organs are increased, whereas SL application has the contrary effect. Based on these observations, we propose a role of the SL-signaling pathway in mediating structural plasticity and water transport capacities in plants in response to fluctuating water availabilities. SUPPRESSOR OF MAX2 1-LIKE 6 (SMXL6), SMXL7 and SMXL8 proteins are transcriptional regulators which are ubiquitinated and subsequently degraded upon the initiation of SL signaling. However, how SL signaling is integrated into developmental programs leading to the formation of vessel elements, i.e. which genes are targeted by SMXL proteins in an SL-dependent manner in developing xylem cells is unclear. This knowledge, however, is key to estimate the significance of environmental integration into plant vascular development and to characterize environment-plant interaction under current and future climatic conditions in a broader spectrum of species. Here, we will generate this knowledge by taking advantage of genetic tools available in Arabidopsis thaliana. Our aim will be achieved by i) elucidation of the SMXL7 chromatin binding profile in a genome-wide fashion, ii) identification of SMXL7-dependent genes in a cambium context and, iii) verification of the relevance of identified targets in the context of vessel formation using genetic and biochemical means.

• DFG Programme: Research Grants