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Shahasad Salam

Candidature

PhD Candidate

Thesis Title

Role of Sugar Sensing in Regulating C4 Photosynthesis and Plant Growth

Project Summary

Shahasad SalamMy thesis project focuses on understanding how sugar sensors regulate physiological responses in the C4 model plant Setaria viridis. Sugar sensors are dual-function proteins crucial to the plant's carbohydrate metabolic pathways. Glucose, produced via photosynthesis, is an essential source of energy and building material for growth. The production of glucose depends on the rate of photosynthesis, which is influenced by environmental factors, such as light intensity, temperature, and nutrient availability. Physiological activities in plants are modulated by glucose availability. Glucose levels are maintained in tissues through feedback mechanisms, which involve sensing glucose molecules via sugar sensors. The expression levels of sugar sensing genes can regulate the activation and inhibition of genes involved in physiological processes, particularly photosynthesis and carbon allocation towards growth.
Various methods in plant physiology, biochemistry, and molecular biology are integrated into this project to elucidate the expression patterns of sugar sensing genes and their influence on photosynthesis and growth. The first chapter characterises the expression patterns of sugar sensing genes in different tissues of two S. viridis ecotypes, MEO34V and A10, grown under ambient and high light conditions using quantitative PCR (qPCR). These two ecotypes exhibit distinct phenotypic characteristics. By exploring the correlation between the expression patterns of sugar sensors in various tissues, this study seeks to understand their role in biomass production and allocation. Photosynthesis will be investigated in vivo through leaf gas exchange measurements and in vitro through assays of key photosynthetic enzymes: phosphoenolpyruvate carboxylase (PEPC), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and nicotinamide adenine dinucleotide phosphate malic enzyme (NADP-ME). These investigations will elucidate how sugar sensors influence photosynthetic efficiency and enzymatic activity. Concurrently, biomass measurements will be conducted to correlate the impact of sugar sensor activity on overall plant growth. This comprehensive approach provides an integrated understanding of how sugar sensors regulate both photosynthesis and growth in two S. viridis ecotypes.
The second and third chapters delve deeper into the roles of specific sugar sensors, such as Hexokinase 6 (HXK6) and Sucrose non-fermenting-1-related protein kinase α1.3 (SnRK1α.3), in regulating photosynthesis and growth in C4 plants under well-watered and water stress conditions. Transgenic lines are developed by overexpressing HXK6 and SnRK1α.3 gene specifically in the mesophyll cells of S. viridis using the ZmPEPC promoter, a mesophyll-specific promoter from maize. Tissue-specific overexpression is performed to understand the influence of these sugar sensors on photosynthesis regulation under varying water availability. This approach is crucial because water availability significantly drives photosynthesis. Investigating the role of these two sugar sensors in leaf tissue ultimately provides insights into photosynthetic efficiency, water-use efficiency, and stress tolerance in plants.
My thesis aims to provide a new set of tools for plant breeders and the scientific community, enhancing our understanding of sugar sensors’ influence on photosynthesis in C4 plants. This knowledge will be vital for crop improvement and food security under future climate conditions.

Supervisors

Professor Oula Ghannoum, Lily Chen