How do plants sense water

Overview

This project combines molecular biological methods with real world problems for agriculture. Increases in global temperatures are leading to periods of drought. In addition, over-irrigation of agricultural land has resulted in salination of arable soils, leading to farmers around the world facing problems of ensuring sufficient farm yields because of the effects of climate change on crop growth and development. Thus it is essential that we understand how plants adapt to stresses such as drought and salinity, and how plants regulate and optimise their use of water. This project will investigate ecological variability in molecular mechanisms by which drought-tolerant or susceptible barley varieties respond to water or salinity stress. This will be compared with the same mechanisms in drought tolerant tropical crops such as millet, quinoa, or sorghum. To do this, we will work on a novel molecular sensor for water stress in plants, and an intracellular pathway that is critical for how plants respond to water stress. QQ21 is an osmosensor that is conserved in protein sequence all the way back to the first land plants (liverworts). The function of this plant plasma membrane protein was discovered as it will complement mutants of the yeast osmosensor ShoI (Fig. 1). In plants, QQ21 is highly expressed during seed development and germination and is upregulated by dormancy and abscisic acid. Mutations in the QQ21 gene results in plants with enhanced salt sensitivity during germination (Fig. 2). Thus, variability in the levels of QQ21 expression or variability in the QQ21 gene and protein sequence may well underlie the differences in drought and salt tolerance of plants during germination and later growth; this is the hypothesis to be explored by the student.

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Image Captions

Fig. 1. QQ21 complements the yeast osmosensor mutant ShoI, permitting growth on high levels of sorbitol (310).
Fig. 2. Germination sensitivity to salt of QQ21 mutant (red bars) and wildtype (blue bars)

Methodology

The key aims of this project are:
(i) identify variation in barley genes for the water sensing pathway in varieties differing in drought tolerance, (ii) test the robustness of this tolerance in the field, (iii) carry out a comparison with stress tolerance mechanisms in tropical cereals.

We have phenotyped over 150 European barley landraces, and 20 elite cultivars for germination under osmotic stress and have identified striking differences; some are tolerant to osmotic stress, others are very intolerant. We will take selected barley varieties and characterise them for gene expression patterns of the osmosensor gene QQ21, and its associated downstream pathway components. We will also look at functionality of variability in the gene and protein sequence of these lines. Additionally, we will compare the expression patterns and sequences of the highly conserved gene QQ21 from tropical crops such as millet and sorghum and quinoa with known drought tolerance traits.

5 sensitive lines and 5 resistant barley lines will be taken and grown under control conditions (green-house and hydroponics) and exposed to stress to monitor the abiotic stress susceptibility of the mature plant. Yield, relative water content, reactive oxygen species and stress gene expression will be monitored in these plants. Q-PCR will be used to measure QQ21 gene expression, and also signalling genes such as MAP kinase kinase 3, known to interact with QQ21 and involved in the transduction of water stress. Expression of stress-induced genes (catalase, ascorbate oxidase, and transcription factors such as MYB1) will be studied. This will yield a description of the role and importance of osmosensor systems in drought tolerance. Gene sequencing for barley alleles of QQ21 associated with abiotic stress resistance, and molecular variants will be functionally tested by cloning into a binary vector harbouring the native QQ21 promoter and complementation of the Arabidopsis QQ21 mutant.
In addition, we will grow drought-tolerant tropical species such as quinoa, millet and sorghum and compare the expression patterns of QQ21 and associated proteins in these plants under control and stress conditions, in order to confirm similarities in osmosensor associated gene expression.
Analysis of the geographic background and the field performance of the barley landraces will be done. This will explore the possibility that abiotic stress resistance comes with the associated cost of a trade-off for other factors that impact on plant growth. Field trials will be carried out over two years in order to monitor important aspects of agronomic performance such as yield and disease resistance of the abiotic stress tolerant and non-tolerant barley varieties.
These experiments will show how plants have adapted to challenging abiotic stress conditions throughout evolution and in our present world, and will provide valuable information on plant breeding strategies for resilient crops for the future.

Project Timeline

Year 1

Growth of barley varieties under control conditions, initiate physiological and molecular analysis of stress tolerant/intolerant barley varieties including sequence analysis of QQ21 alleles.

Year 2

Continue with analysis of barley varieties. Comparisons of gene expression patterns and sequences of key genes with stress tolerant tropical cereal species. Field trials of stress tolerant barley varieties. Genetic complementation of Arabidopsis mutants with variant alleles of QQ21.

Year 3

Field trials of stress tolerant varieties, analysis of data from barley field trials (disease scores, yield).
Preparation of the thesis and journal papers

Year 3.5

Submission of thesis aimed at 3.5 years after commencement of project.

Training
& Skills

The student will have access to IAPETUS2-cohort training, and can make full use of these opportunities in order to develop transferable skills and knowledge. Heriot-Watt University also offers training for postgraduate students. Course sessions cover the four domains of the Researchers Development Framework: A, Knowledge and intellectual abilities: B, Personal effectiveness: C, Research governance and organisation: D, Engagement, influence and impact (www.vitae.ac.uk).
In addition, the student will be trained in a range of scientific methods: molecular biological methods, plant physiology, and data analysis. All methodologies are well established in the applicants’ laboratories.
The student will join a strong set of laboratories working on plant stress. They will use a range of innovative techniques in molecular biology, plant physiology and environmental studies on drought and stress. The project provides for excellent multidisciplinary training and an exciting opportunity to interact between the fields of molecular biology, ecology of environmental stress and plant physiology.

The PhD student will present their results in at least two meetings in the UK and at least one international symposium. The student will also have opportunities to network with project partners at Heriot-Watt and the Centre for Ecology & Hydrology and to become a member of the broader scientific community working on plant stress.

References & further reading

Alexander, R.D., Wendelboe-Nelson, C. Morris, P.C. (2019). The barley transcription factor HvMYB1 is a positive regulator of drought tolerance. Plant Physiol Biochem. 142, 246-253.

Abass, M. and Morris, P. C. (2013). The Hordeum vulgare signalling protein MAP kinase 4 is a regulator of biotic and abiotic stress responses. J. Plant Physiol. 170, 1353-1359.

Qiu, J. L., Zhou, L., Yun, B. W., Nielsen, H. B., Fiil, B. K., Petersen, K., Mackinlay, J., Loake, G. J., Mundy, J. and Morris, P. C. (2008). Arabidopsis mitogen-activated protein kinase kinases MKK1 and MKK2 have overlapping functions in defense signaling mediated by MEKK1, MPK4, and MKS1. Plant Physiol. 148, 212-222.

Wendelboe-Nelson, C. and Morris, P. C. (2012). Proteins linked to drought tolerance revealed by DIGE analysis of drought resistant and susceptible barley varieties. Proteomics 12, 3374-3385.

Further Information

Peter Morris, Institute of Life and Earth Sciences
Heriot-Watt University, Riccarton
Edinburgh, EH14 4AS
Tel +44 (0)131 451 3452
p.c.morris@hw.ac.uk

Ross Alexander, Institute of Life and Earth Sciences
Heriot-Watt University, Riccarton
Edinburgh, EH14 4AS
Tel +44 (0)131 451 3181
r.alexander@hw.ac.uk

Jill Thompson
Centre for Ecology & Hydrology
Bush Estate, Penicuik
EH26 0QB
Tel +44 (0)131 445 8518
jiom@ceh.ac.uk

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