Exploring chemical 'de-priming' and quantitative genetics to improve growth and yield of soybean under abiotic stress.

One of the first changes in plants exposed to environmental stress is an increase of reactive oxygen species (ROS). During evolution, plants have 'learned' to interpret increased ROS as an early warning signal, and to use it as a trigger to induce physiological and biochemical responses that improve their chances of survival. Plant scientists are trying to understand the molecular components of stress signaling pathways and to exploit this information to develop strategies that can improve the stress tolerance of crops in the field. This is particularly important in India where the agricultural production of nutritious crops such as soybean is limited by environmental and climatic challenges arising from soil salinity, drought, water-logging and/or high temperature.

'Chemical priming' has been proposed as a strategy to enhance the natural stress responses of a plant, for example through pre-treatment with low doses of ROS or ROS-producing agents. Indeed, faster or stronger induction of stress responses and improved plant stress tolerance has been reported for ROS-primed plants. However, our previous research in India has shown that the opposite approach - preventing early stress signaling by applying low concentrations of ROS-scavenging agents such as thiourea (TU) - also improves stress tolerance. The solution to this conundrum is likely to reside in the exact environmental condition ('stress scenario') under which tolerance is tested. To ensure survival, plants tend to prepare for the worst-case scenario. One would therefore expect that enhancing the natural plant responses through priming increases survival under severe long-term stress. However, in an agricultural setting some of the natural responses may be unnecessary and unwanted by the farmer. For example, production of stress-protective metabolites is energetically costly and can delay growth and development of the crop. Furthermore, some responses induced by one stress factor may exacerbate problems generated by another stress factor, e.g. closing stomata saves water under salt/drought stress but disables leaf cooling which is essential for combatting heat stress. Thus, if severe long-term stress does not occur, or is prevented through ad-hoc agricultural measures, crop varieties that ignore early stress signals ('happy-go-lucky' plants) could be better suited to farming in India than stress-sensitive ('panicky') varieties that induce strong stress responses. The aim of scenario-driven strategies would be to narrow the margin between actual and possible yield in a given stress situation.

Following this line of argumentation we propose here a research programme that explores the benefits of both chemical and genetic de-priming for soybean production in Indian agriculture. Based on detailed physiological assays in the laboratory and yield data from field experiments we will establish a dose-effect curve of TU-treatments and determine the specific stress scenarios in which this approach improves soybean performance. The optimised TU formulation can immediately be applied in the field. In the longer term, TU application should be replaced by new custom varieties that are hard-wired to ignore early stress signals. To facilitate the development of 'happy-go-lucky' varieties we will therefore also investigate through RNA-sequencing the molecular processes that are targeted by TU, and carry out a genome-wide association study (GWAS) under single and combined salt/TU treatment. GWAS is possible with soybean because a large panel of accessions with re-sequenced genomes is already available. Correlating phenotypic data (root system architecture, biomass, yield) across these accessions with the genomic data will allow us to identify the genetic loci that underpin TU-modulation of stress responses. The information will enable the development of scenario-based custom varieties with improved stress tolerance through marker-assisted breeding or gene editing technology.

The primary aim of the proposed research project is to develop a novel stress-desensitizing approach to boost performance of soybean in the field. In India, more than 6.7 million ha arable land is degraded by salinity, which alongside other abiotic stress factors such as drought, water-logging and heat, hampers plant productivity, thus affecting the livelihood of farmers. Increased soybean production under challenging environmental conditions will not only improve the living of farming community but also help in managing hunger and malnutrition in India. The hidden hunger is a serious problem in developing countries, and the prevalence of underweight, stunting and wasting among children is 48, 43 and 20%, respectively, in India. It accounts for 22% of the burden of disease and adversely affects economic growth with an estimated adult productivity loss of 1.4% of GDP. Soybeans derive ~35-38% calories from protein compared to only 20-30% in other legumes. Soy protein was given the top score in an evaluation of protein quality through the Food and Drug Administration (FDA) and the World Health Organization (WHO), equal to that of meat and milk proteins. Soybean is also one of the very few plant sources of omega-3 fat, which is essential for infants and helps to reduce risk of heart disease and cancer in adults. Due to these benefits, soybean has a prominent place among seed legumes, contributing 25% to the global vegetable oil production. Despite being mainly an agricultural country, India pays an import bill of about $15 billion on edible oils. Additionally, owing to soybean contribution towards maintaining soil fertility through nitrogen fixation, the project will positively impact on the overall agriculture growth and consequently the growing Indian economy. Thus, sustainable soybean production can contribute to socio-economic development in India by increasing the production of protein-rich food.

The funding sought here will be an essential step towards this goal. BARC has a research programme characterising the growth-promoting effects of thiourea, a compound that can scavenge reactive oxygen species that are produced by plants during stress. Increased stress tolerance was reported for several crops and proof-of-concept has been obtained for soybean. The proposed collaborative research will precisely define its mode of action (both in the laboratory and in the field) and on this basis develop strategies for farmers and breeders to desensitize plants against stress. Soybean production is predominantly located in the states of Madhya Pradesh and Maharashtra, which contribute to 89% of total production. Hence, we will be targeting these regions to test thiourea efficacy for improving soybean yield and oil quality in salt, heat and drought affected areas.

While carrying out this project, the UK partner will help building research capacity, improving skills and enhancing the knowledge base of the Indian partner group, which will help in uplifting the quality of science in India. Vice-versa the collaboration offers the UK group access to field sites and breeding capacity, and an opportunity to apply their expertise to a project with immediate impact on food security. The proposed work includes many experimental and computational techniques and therefore offers ample opportunity for training of both Indian and UK personnel.

In summary, project success will lead towards (1) enhancement of soybean production, which can promote the economic development and welfare of India, and (2) strengthening of research excellence in India and the UK. Thus, the topic of the proposed project fulfils the remit of the Newton Fund in general and of the 'Pulses and Oilseed' call in particular.