Regulation of Photosynthesis by Sugar Sensing in C3 and C4 Plants
Photosynthesis is essential for plant fitness. Photosynthesis produces sugars from light, water and carbon dioxide. This provides the plant with the energy required to grow, produce seeds and ultimately survive. When photosynthesis is curtailed, plants remobilise stored resources to promote survival and growth. If plants use more energy than they have available, it can ultimately lead to the depletion of their reserves, starvation and death. It is therefore essential to tightly coordinate photosynthesis, sugar allocation, survival and growth according to environmental and endogenous cues in order to survive and thrive. Sugar sensing plays a key role in coordinating these dynamic relationships. However, little is known about how sugar sensing regulates photosynthesis (particularly C4 photosynthesis). My PhD project addresses this critical knowledge gap in order to better elucidate the role of sugar sensing in higher plants, especially C4, and identify novel ways for improving crop productivity.
My thesis will focus on two key plant sugar sensors: Target of Rapamycin (TOR) and Hexokinase (HXK). I will investigate how these sensors differentially regulate growth and photosynthesis in C3 and C4 model plants. Initially, I will analyse the genetic structure and evolution of these sugar sensors by relating all orthologues found across various C3 and C4 species. I will decipher not only if, but when in evolutionary history they diverged and what were the residues involved. Secondly, to tease apart the functional roles that these sensors play within C3 and C4 plants, I will use in planta down- and up-regulations of TOR and HXK levels targeted to the mesophyll cells, where photosynthesis and initial CO2 fixation occur in C3 and C4 plants, respectively. I will then examine the effects of these manipulations on growth and photosynthesis in both C3 and C4 plants. Finally, I will use environmentally induced changes in sugar levels in wild type and transformant plants in order to identify how such changes will impact sugar sensing, photosynthesis and the leaf transcriptome.
A/Professor Oula Ghannoum, Dr Alex Watson-Lazowski, Dr Clemence Henry, Professor Robert Furbank (ANU)