Rice is one of the most commonly grown crops consumed by almost half of the population worldwide. As the demand increases, rice cultivation is extending into areas with scarce resources and unfavorable conditions. One of the major abiotic stresses is salinity, which plays a big role in determining yield and growth. Therefore, there is a pressing need to introduce salt-tolerant varieties of rice as rice displays the highest sensitivity to salt stress. Extensive research has revealed that genetic, molecular, and physiological mechanisms control the salt tolerance of different crops.
To this note, scientists from the University of Tasmania: Professor Sergey Shabala, Associate Professor Lana Shabala, Professor Holger Meinke, Professor Meixue Zhou, Tianxiao Chen and Yanan Niu in collaboration with Professor Zhong Hua Chen from Western Sydney University, Dr. Gayatri Venkatraman from M.S. Swaminathan Research Foundation, Professor Ashwani Pareek from Jawaharlal Nehru University and Professor Jianlong Xu from Chinese Academy of Agricultural Sciences critically reviewed the present understanding of the mechanisms of salt tolerance exhibited by rice crops, which was published in the Crop journal.
Professor Zhou said to Science Feature that: “To date, large numbers of genes involved in various salt-tolerant mechanisms in rice have been identified. Therefore, understanding their function and crosstalk at the molecular level could provide valuable information for improving salt tolerance in rice.”
Professor Zhou and colleagues initially evaluated the current literature on gene networks responsive to salt stress. Then, they delved into detail about how stress sensing and signaling pathways and reactive oxygen species scavenging of rice crops can help in the development of new salt-tolerant rice cultivars. However, according to the researchers, it is difficult to establish a definite connection between gene networks and salt tolerance in rice. Most of the literature was derived from reverse genetic approaches on the plant Arabidopsis despite the genetic similarity.
Later, the research team demonstrated how stomatal regulation, osmotic adjustment, ion homeostasis could hinder salt tolerance on a functional level. The high salt content can markedly reduce the uptake of water in the plant, resulting in lower stomatal conductance. High salinity causes elongated plant cells at a cellular level, decreased uptake of water, and impaired leaf development. The researchers proposed that mining and combining favorable alleles linked to salt tolerance is a better approach to improve the germplasm.
Inadequate genetic resources with high salt tolerance are the main reason that little progress has been made in creating newer salt-tolerant rice varieties. The key to successful improvement in salt-tolerant crops lies in the profound understanding of the molecular mechanisms. The researchers recommend precise genome editing technology, the use of genes involved in stress sensing and signaling, and the use of target editing of miRNAs to develop salt-tolerant rice cultivars. They also proposed that more importance should be placed at reproductive stage salt tolerance, contributing to better yield. Finally, a suggestion was made to target the multi-stress responsive genes, followed by testing the salt-tolerant rice crops under real-life conditions to assess the impact of salinity.
In summary, owing to the increasing environmental stresses due to climate change, there is an imminent need to produce genetically modified salt-tolerant rice crops to meet the energy demands of the growing global population. “An important next step would be to test the genetically engineered plants under field conditions to evaluate their stress tolerance and then model their responses in order to obtain a global assessment of the likely impact of such improved varieties, “said Professor Xu. The findings from this comprehensive review will guide future attempts to develop newer salt-tolerant rice cultivars.
Chen, Tianxiao, Sergey Shabala, Yanan Niu, Zhong-Hua Chen, Lana Shabala, Holger Meinke, Gayatri Venkataraman, Ashwani Pareek, Jianlong Xu, and Meixue Zhou. “Molecular mechanisms of salinity tolerance in rice.” The Crop Journal (2021). DOI: https://doi.org/10.1016/j.cj.2021.03.005
About the Authors
Meixue Zhou, Ph.D
Professor Zhou has been involved in agricultural research for nearly 40 years. In the last 15 years, he has published more than 150 refereed papers. Most of the papers are published in high IF journals and, more importantly, his publications showed greater impact with over 9,000 citations.
His major research interests are improving the stress tolerance of plants (waterlogging, salinity, acid soils and disease). His pre-breeding program covers the whole spectrum from trait discovery to variety development. These include 1) applied research: germplasm screening for specific traits (stress tolerance), accurate phenotyping and cell-based phenotyping to discover key traits or mechanisms conferring tolerance; and 2) genetics and breeding: discovery of genes/QTL, molecular markers linked to the traits, and development of pre-breeding materials and varieties (with breeding companies). He has established a strong research team that involves physiologists, molecular biologists and agronomists, investigating interactions between genotypes and environment (soils, seasonal rainfall & temperature and changing climate) and management (Agronomy – varieties with matching agronomic practices, precision agriculture, irrigation and modelling). He has established reliable screening facilities for various stress tolerances and developed a method for fast introgression of specific traits to commercial varieties. He has demonstrated excellence in the supervision of postgraduate students. He has successfully supervised to completion of 30 Ph.D.’s and five Master’s students who have gone onto successful research careers. Each Ph.D. student producing more than three published papers. He is currently supervising 16 Ph.D. students.
Jianlong Xu, Ph.D.
Professor Xu has been major in rice genetics and breeding for more than 30 years. In the past 20 years, he has published more than 130 refereed papers, most of which involved gene/QTL identification, allele mining and marker-assisted breeding for abiotic and biotic stress tolerances and yield-related traits in rice crop. He obtained one First National Prize for Scientific & Technological Advancement and two first Provincial Prizes for Scientific & Technological Advancement in the last five years. Six rice varieties have been nationally approved and nine have been provincially approved. In addition, 12 patents and nine variety rights have been successfully applied. So far, he has successfully supervised to completion of three post-doctoral, 10 Ph.D. and 25 Master’s students, and is currently supervising three post-doctoral, four Ph.D. and four Master’s students.
To effectively integrate QTL mapping with QTL-based rice molecular breeding, he has been advocating a selective introgression strategy. This strategy has been practiced for genetic dissection, allele mining and simultaneous improvement of complex traits in rice, by developing large numbers of trait-specific introgression lines (ILs) using backcross breeding in elite genetic backgrounds. Multiple complex traits can be simultaneously improved by designed QTL pyramiding based on the performance of target traits and QTL alleles underlying the traits of ILs. Now, he is focusing on allele mining of previously important cloned genes using 3K re-sequenced rice accessions collected from worldwide, then accurately improve the target traits of elite variety by gene-editing based on the favourable allele information.
Main Image Credit: iAGRI Tanzania, Flickr