Salinity tolerance in barley during germination- homologs and potential genes

Abstract

Salinity affects more than 6% of the world's total land area, causing massive losses in crop yield. Salinity inhibits plant growth and development through osmotic and ionic stresses; however, some plants exhibit adaptations through osmotic regulation, exclusion, and translocation of accumulated Na+ or Cl-. Currently, there are no practical, economically viable methods for managing salinity, so the best practice is to grow crops with improved tolerance. Germination is the stage in a plant's life cycle most adversely affected by salinity. Barley, the fourth most important cereal crop in the world, has outstanding salinity tolerance, relative to other cereal crops. Here, we review the genetics of salinity tolerance in barley during germination by summarizing reported quantitative trait loci (QTLs) and functional genes. The homologs of candidate genes for salinity tolerance in Arabidopsis, soybean, maize, wheat, and rice have been blasted and mapped on the barley reference genome. The genetic diversity of three reported functional gene families for salt tolerance during barley germination, namely dehydration-responsive element-binding (DREB) protein, somatic embryogenesis receptor-like kinase and aquaporin genes, is discussed. While all three gene families show great diversity in most plant species, the DREB gene family is more diverse in barley than in wheat and rice. Further to this review, a convenient method for screening for salinity tolerance at germination is needed, and the mechanisms of action of the genes involved in salt tolerance need to be identified, validated, and transferred to commercial cultivars for field production in saline soil.

Keywords: Genetics; Barley; Quantitative trait locus (QTL); Germination; Salinity tolerance; Homologous gene; Diversity.

Fig. 1

Interactions among the hormones and gene regulatory pathways in barley during germination under salinity stress Blue lines indicate hormonal regulation, while black lines are for genes and transcription factor expression. Red double-arrowed dotted line shows the negative interaction between ABA and GA during germination, while blue double-arrowed line shows the positive interaction among the hormones. Blue dotted lines show the stimulation outcome of the hormonal interactions, while black dotted lines show the regulatory interactions of genes. GAMYB: GA-induced Myb (myeloblastosis)-like protein; HvPTR: barley scutellar peptide transporter; HvKAO1: barley kaurenoic acid oxidase 1; HvGA2ox: barley GA 2-oxidase 1; HvNCED: barley nine-cis-epoxycarotenoid dioxygenase; PP2C: protein phosphatase type 2C; ABI1: ABA-insensitive 1; HvABA8′OH-1: barley ABA 8' hydroxylase; HvCBL: barley calcineurin B-like protein; HvSERK: barley somatic embryogenesis receptor-like kinase; HvCBF: barley C-repeat-binding protein; HvDREB: barley dehydration-responsive element-binding protein; HvRAF: barley root abundant factor; HvPIP2;5: barley aquaporin 2;5

Fig. 2

Phylogenetic analyses of barley homolog genes (a) Dehydration-responsive element binding proteins. (b) Somatic embryogenesis receptor-like kinases. The unrooted phylogenetic trees of 37 (a) and 92 (b) domains comprising four (a) and five (b) domains, respectively, from barley were constructed using MEGA-X

Fig. 3

Phylogenetic analysis of barley homolog aquaporin genes The unrooted phylogenetic tree of 74 domains comprising five domains from barley was constructed using MEGA-X