Creating climate change-resilient crops
The Keystone meeting on Climate Change-Linked Stress Tolerance in Plants took place in Hannover, Germany in May, bringing together researchers from all over the world with the goal of increasing global food security in a changing climate.
Ending hunger, achieving food security, increasing nutrition, and promoting sustainable agricultural practices are a major sustainable development goal. At the same time, climate change is making this goal more difficult to reach by impacting agriculture and food security on a global scale. Developing countries produce 78% of the world’s food, and these areas are particularly susceptible to the impacts of climate change, including high heat, drought, sea level rise, increased flooding, and air pollution. Last week, at the Keystone meeting on Climate Change-Linked Stress Tolerance in Plants, plant researchers attempted to address this issue head-on.
The conference was attended by a great mix of students, post-docs, early-career and established researchers coming from 25 countries, including those facing the harshest effects of climate change. Researchers from Mexico, India, Nigeria, Cameroon, and South Africa were able to attend thanks to support from Keystone sponsors and local governments.
The themes covered by this conference were diverse, showing the complexity and urgency of solving these problems. Here, I highlight a few of the main ideas discussed at the meeting. All abstracts can be viewed on the meeting website.
Improving water-use efficiency
Water-use efficiency refers to the ratio of water used by plants in metabolism to water lost during transpiration. 98% of water that is taken up by roots is lost during transpiration. During photosynthesis, plants assimilate carbon using light energy as a driver for the carbon fixation pathway. The plants use pores in their leaf surfaces, called stomata, to take in CO2 from the atmosphere, which has the side-effect of losing water vapour. Plants alter their water-use efficiency under drought conditions – following detection of abscisic acid originating in the root – by shutting down photosynthesis, and so the two processes seem to be diametrically opposed.
Julie Gray (University of Sheffield) has been working on engineering stomata as a potential solution for improving crop water use while maintaining carbon fixation. Her lab has identified a gene responsible for inhibiting stomatal development (EPF2), thereby stopping inappropriate stomatal development. Deficiency in this gene leads to higher stomatal density, while its overexpression reduces the number of stomata on the leaf surface. But CO2 assimilation changes only slightly with both reduced and increased stomatal density. In plants with a lower number of stomata, water-use efficiency is higher, making the plants more tolerant to drought and preserving soil water content. The Gray group has also found similar genes in cereals, like rice, Brachypodium, and barley. They have created a rice line with low stomatal density, resulting in rice with higher yield under drought conditions.
Another potential strategy for improving water-use efficiency is the harnessing of abscisic acid signalling by manipulating specific abscisic acid receptors. Erwin Grill (Technical University Munich) presented his work on this, showing an increase in water productivity with no marginal trade-offs in crop growth and yield.
Improving abiotic stress resilience
A changing climate means that crops are going to be exposed to increased heat, drought, changes in soil salt concentrations, and waterlogging in areas prone to flooding.
Maria von Korff Schmising (University of Düsseldorf) discussed the importance of exploiting genetic diversity in crop wild relatives to introduce important stress resistance genes into crop lines. In her case, she has been working on improving heat tolerance in barley by breeding with barley wild relatives. Her group identified a number of genes in the wild relative that maintain floret fertility, pollen development, and seed number even under high heat. These traits were successfully transferred to an elite barley line via breeding.
We also learned about some of the tricks used by ‘resurrection plants’ like Tripogon loliiformis, which are able to survive desiccation, and how we can apply these lessons to crop plants. Brett Williams (Queensland University of Technology) found that many of the genes involved in programmed cell death and aging are downregulated in this plant while drying out, and that survival genes are highly expressed – the opposite of what we see in non-resurrection plants! While most plants will put energy into flowering and reproduction when exposed to stress, T. loliiformis and other desiccation tolerant plants instead focus energy on maintaining cellular processes to encourage recovery. The Williams lab has introduced some of the resilience genes into crops like chickpea, resulting in increased tolerance and larger seeds.
Japan and other Asian countries face changes in rainfall distribution and potential flooding, and so finding strategies to improve crop tolerance to waterlogging is a priority in this region. Mikio Nakazono (Nagoya University) discussed differences in airy tissues (aerenchyma) supplying oxygen to roots in rice and maize. Rice grows well in flooded soil because of well-developed aerenchyma and structures in the root that allow oxygen to reach the root tip rather than being lost to the soil. His lab identified genes responsible for development of both aerenchyma and this barrier in rice, with the hope of transferring these to other crops lacking these strategies. Luckily, a maize wild relative (teosinte) already has these genes, and so the group is working on introducing these genes into elite maize lines to promote waterlogging tolerance.
Improving response to elevated greenhouse gases
Greenhouse gases in the Earth’s atmosphere include water vapor, CO2, methane, and ozone. With a changing climate comes an increase in the concentration of greenhouse gases in the atmosphere, particularly affecting croplands in the Middle East, Asia, sub-Saharan Africa, the Amazon, and parts of the USA. Ozone damages plants by entering through the stomata and forming other reactive oxygen species, leading to altered hormone response, transcription of genes, and even photosynthesis. Lisa Ainsworth from the University of Illinois spoke about her work on reducing crop losses in response to increased greenhouse gases. Her lab has found resistant maize genotypes for breeding ozone tolerance. The resistance maize line show accelerated senescence, reduced capacity for photosynthesis, but an increase in seed yield.
Much of the work being done to improve crop yield in a changing climate looks to exploit genetic diversity in both crops and their wild relatives. Studying mechanisms of resilience in extremophiles – species able to survive and thrive under extremely stressful conditions – could also improve crop performance. It certainly is an exciting time for plant researchers addressing and promoting sustainable agriculture in the face of climate change, and we look forward to seeing how the field develops.