What rising CO2 does to one of world’s most important protein sources
A combined physiological and transcriptomic approach provides insights into the molecular dynamics and gene regulation of the responses to CO2 stress. Photo: ICRISAT
In their effort to ensure food and nutrition security in the face of rising carbon dioxide levels and climate change, researchers at ICRISAT, in a first of its kind study, have demonstrated what elevated CO2 does to chickpea and have uncovered the molecular basis for these effects. Several important plant metabolic pathways related to sugar/starch metabolism, chlorophyll and secondary metabolites biosynthesis were found to be affected.
Their study, ‘Molecular and Physiological Alterations in Chickpea under Elevated CO2 Concentrations’ published in the journal Plant & Cell Physiology, shows that elevated CO2 levels cause the roots and shoots of the plants to grow taller with significantly altered nodulation, total chlorophyll content and nitrogen balance index that accelerates plant senescence.
Rising CO2 levels
Since the industrial revolution, global atmospheric carbon dioxide (CO2) concentrations have rapidly increased, rising from 280 ppm to currently exceeding 400 ppm. Predictions warn that the global CO2 concentration will continue to rise and affect major food crops both positively and negatively.
Many of these effects are yet be fully understood in most crops. For the semi-arid regions, where chickpea is a widely cultivated legume, a rich and an important source of protein, food and nutrition security of the future hinges on identifying climate-change related plant changes and the molecular basis for these.
While there are crop varieties that are resilient to stresses such as drought, elevated temperature and diseases, the researchers note that plants have not evolved specific mechanisms to respond to elevated CO2 levels.
The study
The study’s authors, a team of researchers from ICRISAT’s Center of Excellence in Genomics and Systems Biology (CEGSB) and the Centre of Excellence in Climate Change Research for Plant Protection (CoE-CCRPP), subjected two chickpea varieties widely grown in India, JG 11 (desi) and KAK 2 (Kabuli), to elevated CO2 in open top chambers at CoE-CCRPP.
One chamber was maintained at current ambient CO2 level of 380 ppm (control), the other chambers were maintained at elevated levels of 550 pm and 700 ppm. The plants were sown under stress conditions and harvested during vegetative stage and reproductive stage, 15 days and 30 days respectively, post germination.
The researchers observed common physiological changes and cultivar-specific changes during both growth stages at elevated levels of CO2.
To investigate the molecular basis for these changes, CEGSB collected RNA-Seq based transcriptome (gene expression through RNA) data from 12 physiologically evaluated plant samples at different stages under control and elevated CO2 concentrations. Transcriptome analysis identified 18,644 differentially expressed genes (DEGs). Among these are genes responsible for root and shoot development, sugar metabolism, porphyrin and chlorophyll metabolism and other second metabolites synthesis pathways, which play a key role in the plant’s defense mechanism. The study also identified higher number of DEGs altered at reproductive stage and at 700 ppm CO2 due to prolonged exposure at higher stress point when compared to vegetative stage and 500 ppm elevated CO2.
The differential expression profiles of key candidate genes were further validated by quantitative Real Time-PCR, a highly effective tool for gene expression validation. It was noted that the molecular level changes were more pronounced in Kabuli type (KAK 2) at reproductive stage.
“The present study will act as a model system for studying the effect of greenhouse gases in plants. Moreover, exploring the cultivar-specific, stage-specific and stress response-specific response of plant upon elevated CO2 concentrations and identification of key major metabolic and stress signaling pathways could help to identify the candidate gene pools and be useful in developing climate-resilient crops,” the researchers concluded.
The study was partially supported by Government of India’s Department of Biotechnology, Department of Science and Technology (Climate Change Program) and Bill & Melinda Gates Foundation. It was undertaken as part of CGIAR Research Program on Grain Legumes and Dryland Cereals (CRP-GLDC).
