Opportunities for Improving Waterlogging Tolerance in Cereal Crops-Physiological Traits and Genetic Mechanisms

Abstract

Waterlogging occurs when soil is saturated with water, leading to anaerobic conditions in the root zone of plants. Climate change is increasing the frequency of waterlogging events, resulting in considerable crop losses. Plants respond to waterlogging stress by adventitious root growth, aerenchyma formation, energy metabolism, and phytohormone signalling. Genotypes differ in biomass reduction, photosynthesis rate, adventitious roots development, and aerenchyma formation in response to waterlogging. We reviewed the detrimental effects of waterlogging on physiological and genetic mechanisms in four major cereal crops (rice, maize, wheat, and barley). The review covers current knowledge on waterlogging tolerance mechanism, genes, and quantitative trait loci (QTL) associated with waterlogging tolerance-related traits, the conventional and modern breeding methods used in developing waterlogging tolerant germplasm. Lastly, we describe candidate genes controlling waterlogging tolerance identified in model plants Arabidopsis and rice to identify homologous genes in the less waterlogging-tolerant maize, wheat, and barley.

Keywords: Arabidopsis; QTL; barley; candidate genes; maize; rice; waterlogging tolerance mechanism; wheat.

Figure 1

Schematic diagram of the main waterlogging stress responses and metabolic adaptive traits for waterlogging tolerance in plants. PDC: pyruvate decarboxylase, ADH: alcohol dehydrogenase, RBOH: respiratory burst oxidase homolog, GST: glutathione S transferase, XET: xyloglucan endo-transglycosylase, ACO: 1-amino-cyclopropane-1-carboxylic acid oxidase.

Figure 2

Homologous candidate genes for waterlogging tolerance in rice, maize, barley, and wheat. WRKY: WRKY transcription factor family, GST: glutathione S transferase, RBOH: respiratory burst oxidase homolog, HMS: heavy metal transport/detoxification superfamily protein, ERF: Ethylene-responsive factor. Each bar represents the individual chromosome, and the chromosome name is placed in the middle of the bar. The purple bars indicate 12 chromosomes of rice; the orange bars indicate 10 chromosomes of maize; the grey bars indicate 7 chromosomes of wheat A, B, D genome; the red bars indicate 7 chromosomes of barley. Gene name placed on the chromosome bar based on the physical position.