Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - Pod Yield (“Can bean yield losses caused by drought, heat stress and climate change be ameliorated by enhancing pod-specific stomatal conductance?”)

Teaser

Droughts in Mexico reduce agricultural production and cause major damage to livelihoods, costing £billions to the economy. Mexico’s reliance on rain-fed agriculture, and its arid zones, makes it vulnerable to drought, yield loss, and soil degradation. Mexico’s geography...

Summary

Droughts in Mexico reduce agricultural production and cause major damage to livelihoods, costing £billions to the economy. Mexico’s reliance on rain-fed agriculture, and its arid zones, makes it vulnerable to drought, yield loss, and soil degradation. Mexico’s geography, population, and urbanisation with habitat loss, make it exposed to the effects of overexploitation of resources, droughts, and climate change. Common bean is the most important grain legume in human diets, and a major source of nutrition. Mexico is a centre of origin, domestication, and diversity for beans, and they are central to Mexican culture and Latin American and African food security. Drought stress is a major concern because most bean agriculture is rain-fed, not irrigated. The development of novel bean varieties and production of beans with greater climate change resilience will impact positively on the poorest communities reliant on timely rains, as well as global Food Security. The overall objectives are to identify mechanisms of drought tolerance from the related desert species, tepary bean, and translate these into common beans to improve water deficit resistance. Characterising drought responses through developmental, physiological, and transcriptomic analyses will help us understand divergent approaches to stress resilience. Stomata are microscopic valves on leaf and pod surfaces that control water loss and CO2 uptake for photosynthesis. By altering stomatal traits such as size and density, we can improve water use efficiency. In this project we will compare stomatal traits across beans and use this information to enhance drought resilience to make ‘Climate Smart’ bean crops for Latin American agriculture. By improving water use of bean crops, we can promote more resilient systems of production under climate change, improve economic securities for farmers and maintaining sustainable sources of healthy food.

Work performed

\"Comparative analyses of drought responses have been undertaken between the Mexican P. vulgaris germplasm Pinto Saltillo versus high-yielding drought resistant domesticated tepary elite-bred USDA TARS #32 germplasm. Confocal imaging has been utilised for early stages in stomatal development and mature pod epidermal impressions were used to determine stomatal densities, indices, cell and stomatal pore size traits. These demonstrated contrasts in stomatal developmental responses, suggesting alternative strategies to cope with drought. These responses informed the direction of the project to attempt to control pod-specific mass flow and stomatal conductance under drought, in line with the superior responses of tepary. The reduction of transpiration rate afforded by the reduced stomatal densities observed in tepary translate to longer term maintenance of water status and maintained gas exchange under water deficit.
RNAseq experiments are underway to determine developmental and physiological responses of the stomata of the source leaves and pods with the aim of qualifying stress response synchronisation between tissues and species. However it is possible that terminal drought signals impact the plant after epidermal developmental signals are set. In this scenario it may only be stomatal physiological plasticity that can modulate the response in source leaves.
Improving bean drought tolerance. Based on tepary drought responses, the promotion of stomata may be too simplistic to afford increased mass flow to the pod and yield under drought. The comparative experiments rather allude to reduction in stomatal numbers to prolong water supply to the pod under drought and to achieve this, I took the same approach as I have taken successfully in rice, harnessing a universal control mechanism to modulate stomatal patterning, involving Epidermal Patterning Factors to enhance water use and drought tolerance in bean. Aided by a joint Master’s Student with Prof. Covarrubias, Brianda de la Sancha, I am testing functional orthology of bean EPFs by over-expression and complementation and these data are directing our decision-making. Our attempts to increase stomatal density of bean pods involved two methodologies, synthetic peptide application and estradiol induction in Arabidopsis. Another option would be to obtain pod-specific promoters and several are reported in the literature. However, transcriptomic data from resources such as Phytozome suggest that none are sufficiently pod specific. We will probe our RNAseq data to try to identify pod promoter sequences. Transient transformation of Phaseolus embryos, using transformation techniques optimised by Dr. Francisco Aragão (EMBRAPA, Brazil) and reported in Pinto Saltillo by Dr. Rocío de la Garza (Tech. de Monterrey), were successful at IBt; transient GUS expression using an overexpression plasmid shows that the construct works in vivo. However, issues with selective herbicide agent, and lack of germination of putative positive control transgenic Pinto Saltillo seeds, suggest that the techniques remain inefficient. Based on these results, I chose to address the question using an alternative legume species, soybean and constructs have entered transformation pipelines. Soybean forms the basis of the Masters project of IBT student Brianda de la Sancha (jointly supervised by myself and Prof Covarrubias), and is now central to a Royal Society Newton Fund Mobility Grant I established between the labs of Prof. Covarrubias and Prof. Gray, enabling her to undertake experiments under my supervision in Sheffield in 2020.As Mexican research centres do not have CO2 enrichment facilties, investigation of future climate scenarios are being performed with Prof. Gray at Sheffield. In this way we can understand plant responses to CO2 and drought in these lines.\"

Final results

This MSCA IF GF has set the foundation for UK-Mexico research in bean drought improvement. We will obtain transcriptomic analyses of drought tolerant bean water deficit strategies to identify new candidate genes for crop improvement. We hope to test mutant and transgenic beans in response to drought under future levels of CO2. Long term positive impacts include fewer crop losses, greater yields to improve farmer profits and community wealth and health, to improve socio-economic issues and enhanced resilience and sustainable intensification of legume agriculture. Testament to the project’s successes, we were awarded the Newton Prize Mexico 2018, which will fund a one-year experiment between the labs of Prof. Covarrubias, Prof. Georgina Hernandez (CCG), and Prof. Gray. The MSCA IG GF has laid this foundation, and the Newton Prize research will also identify mutants in water use and nitrogen use traits (e.g. rhizobial nodulation) through Whole Genome Sequencing. Upon completion of the MSCA IF GF, the collaborations and experiments will continue between UNAM, Sheffield, and myself as I will take up a permanent Research Leader role in the Royal Botanic Gardens, Kew, as a member of the Plant Resources team of the Department of Natural Capital. Kew has a long history of collaboration with Mexico, and legume expertise. This position will ensure fruitful application into legume breeding and will increase impact to benefit Latin American collaborations, agriculture, Food Security, and society for years to come.

Website & more info

More info: http://www.podyield.org.