Scientists innovate breeding strategies to create climate-smart crops

A recent study has reported a novel breeding strategy to rapidly create climate-smart crops that show higher yield under normal conditions and greatly rescue yield losses under heat stress both in staple grain and vegetable crops.

The study, which was published in Cell on 13 December, was conducted by Prof. XU Cao’s team from the Institute of Genetics and Developmental Biology (IGDB) of the Chinese Academy of Sciences.

The year 2050 is fast approaching and farm productivity must increase by 60% in order to feed a projected global population of 10 billion. However, current crop production is insufficient and is expected to worsen due to the abiotic-stress burden of climate change.

An increase of 2 °C during the growing season will result in a yield loss of 3–13%. To ensure global food security and overcome breeding bottlenecks, scientists urgently need to develop “climate-smart” crops that achieve higher yields under normal conditions and stable yields under heat stress.

The physiological basis of crop yield and quality is the source-sink relationship. Source tissues (e.g., leaves) are net producers of photoassimilates—i.e., primarily carbohydrates such as sucrose. In contrast, sink tissues (e.g., fruits, seeds, roots, developing flowers, cotton fibers, and storage organs) are net importers, which use or store photoassimilates.

The cell wall invertase gene (CWIN) is the crucial gene regulating the source-sink relationship in plants. The enzyme encoded by this gene unloads and converts sucrose transported from leaves into glucose and fructose within sink organs, where these sugars can be directly absorbed and utilized. These sugars are not only essential nutrients for the development of fruits and seeds, but significantly influence the sweetness of fruits and the quality of rice grains.

Heat stress represses CWIN activity and thus disrupts the source-sink balance, resulting in inadequate energy supply in sink organs, reduced reproductive development, and yield penalties.

In their new study, Prof. XU Cao and his team developed a strategy based on climate-responsive optimization of carbon partitioning to sinks (CROCS) by rationally manipulating the expression of CWIN genes in fruit and cereal crops. They precisely knocked-in a 10-bp heat-shock element (HSE) into promoters of CWIN genes in elite rice and tomato cultivars, using self-developed high-efficiency, prime-editing tools. HSE insertion endows CWINs with heat-responsive upregulation in both controlled and field environments to enhance carbon partitioning to rice grains and tomato fruits.

Multi-location and multi-season yield tests on tomatoes under various cultivation conditions including greenhouses and open fields showed that under normal conditions, the CROCS strategy increased tomato yields by 14% to 47%. Under heat stress, it increased per-plot fruit yield by 26%~33% over controls and rescued 56.4%~100% of fruit yield losses caused by heat stress. Notably, aspects of fruit quality such as uniformity and sugar content were significantly improved compared to unmodified controls.

In addition, rice cultivars improved by this strategy not only showed a yield increase of 7% to 13% under normal conditions, but also showed a 25% grain yield increase over controls under heat-stress conditions. Specifically, up to 41% of heat-induced grain losses were rescued in rice.

Prof. Xu noted that CROCS is an efficient, versatile, prime-editing based system for rapid crop improvement, which paves the way to rapidly create climate-smart crops by targeted insertion of environment-responsive cis-regulatory elements. The strategy also provides effective gene-editing tools and feasible operational procedures for the fundamental study of plant responses to stress.

The researchers also noted that this breeding strategy has now also been applied to crops such as soybeans, wheat, and corn.