The role of chloroplasts in responding to drought stress in plants

Programme website: http://inspire-dtp.ac.uk

Project Rationale:
Food security is a major problem facing the World and one that is going to become more pressing in coming decades due to increased population and new challenges imposed by climate change (1). With a limit on irrigation, much of the estimated 50% increase in productivity required by 2030 will need to come from rain-fed agriculture and thus drought is the major abiotic stress limiting crop yields worldwide. Since photosynthesis is so sensitive to the environment, the chloroplast plays a central role in the response of plants to environmental stresses including drought. For drought stress, there is an increasing body of evidence that enhancement of the chloroplast-localised tetrapyrrole pathway through treatment with tetrapyrrole precursors can protect plants (2). Although the mechanism is not well understood, heme synthesis is suggested to be the critical factor. Heme is also a key player in communication between the chloroplast and nucleus (3) and our own transcriptomic results show some overlap between retrograde- and drought-responsive genes. In this project we will test the hypotheses that activation of chloroplast-to-nucleus retrograde signalling protects against drought and that drought modifies the chloroplast proteome to bring about these changes in retrograde signalling.

Methodology:
The project will take two approaches to test these hypotheses. Firstly, the model plant Arabidopsis will be used to test whether mutant and transgenic plants with altered heme metabolism and retrograde signalling show differences in their tolerance to drought stress. All lines are already available in the laboratory and analysis of drought responses will include measurement of drought-sensitive gene expression by real-time qPCR. We also have evidence that retrograde signaling is dependent on interaction between the ribosome and tetrapyrrole biosynthesis enzymes within the chloroplast. We will therefore examine the impact of drought stress on the chloroplast proteome as a whole and also specifically on the interaction of these protein classes. This will generate a unique data set for the impact of this environmental stress on chloroplasts. Secondly, we will feed tetrapyrrole precursors to plants and examine their impact on drought responses. Feeding experiments will be performed with Arabidopsis and also with wheat, one of the World’s major crops. Under conditions in which feeding successfully protects against drought we will use RNAseq analysis (performed in the Environmental Sequencing Facility at SOES) to determine global changes in gene expression. Comparison with known retrograde signalling datasets will directly address our first hypothesis.

Training:
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the School of Biological Sciences. Specific training will include: plant stress physiology; analysis of gene expression by real-time quantitative PCR, which is routinely performed in the laboratory, and by RNAseq in the Environmental Genomics Facility at SOES; and targeted and quantitative proteomics in the Centre for Proteomic Research within the School for Biological Sciences. The co-supervisor is Director of the Centre and will provide expert training in these techniques.