Salinity is one of the limiting factors of wheat production worldwide. A total of 334 internationally derived wheat genotypes were employed to identify new germplasm resources for salt tolerance breeding. Salt stress caused 39, 49, 58, 55, 21 and 39% reductions in shoot dry weight (SDW), root dry weight (RDW), shoot fresh weight (SFW), root fresh weight (RFW), shoot height (SH) and root length (RL) of wheat, respectively, compared with the control condition at the seedling stage. The wheat genotypes showed a wide genetic and tissue diversity for the determined characteristics in response to salt stress. Finally, 12 wheat genotypes were identified as salt-tolerant through a combination of one-factor (more emphasis on the biomass yield) and multifactor analysis. In general, greater accumulation of osmotic substances, efficient use of soluble sugars, lower Na+/K+ and a higher-efficiency antioxidative system contribute to better growth in the tolerant genotypes under salt stress. In other words, the tolerant genotypes are capable of maintaining stable osmotic potential and ion and redox homeostasis and providing more energy and materials for root growth. The identified genotypes with higher salt tolerance could be useful for developing new salt-tolerant wheat cultivars as well as in further studies to underline the genetic mechanisms of salt tolerance in wheat.

Improvement of low nitrogen (LN) tolerance or nitrogen use efficiency (NUE) in crops is imperative for environment-friendly agriculture development. The basic helix-loop-helix (bHLH) transcription factors are involved in multiple abiotic stresses and are suitable as candidate genes for improving LN tolerance. Few studies were performed on the characterization of the HvbHLH gene family and their function in response to LN stress in barley. In this study, 103 HvbHLH genes were identified through genome-wide analysis. HvbHLH proteins were classified into 20 subfamilies based on phylogenetic analysis in barley, which was supported by conserved motifs and gene structure analysis. The stress-related cis-element analysis in the promoters showed that HvbHLHs are probably involved in multiple stress responses. By phylogenetic analysis of HvbHLHs and bHLHs in other plants, some HvbHLHs were predicted to play roles in response to nutrition deficiency stress. Furthermore, at least 16 HvbHLHs were differentially expressed in two barley genotypes differing in LN tolerance under LN stress. Finally, overexpression of HvbHLH56 enhanced LN stress tolerance in transgenic Arabidopsis, suggesting it is an important regulator in LN stress response. The differentially expressed HvbHLHs identified herein may be valuable for the breeding of barley cultivars with LN tolerance.

Background: Improvement of low nitrogen (LN) tolerance or nitrogen use efficiency (NUE) in crops is imperative for environment-friendly agriculture development. The basic helix–loop–helix (bHLH) transcription factors are involved in multiple abiotic stress, suitable as the candidate genes for improving LN tolerance. Little research was done on characterization of bHLH gene family and their response to LN stress in barley.Results: In this study, 168 bHLH genes were identified in barley through genome-wide analysis. HvbHLH proteins were classified into 26 subfamilies based on phylogenetic analysis with bHLH proteins from Arabidopsis thaliana and rice. The analysis of conserved motifs and gene structures supported the evolutionary relationships among these HvbHLH proteins. Further, analysis of stress-related cis-elements in the promoter regions showed that bHLH proteins in barley are probably involved in multiple stress responses. Finally, at least 16 bHLH genes were differentially expressed in two barley genotypes differing in LN tolerance under LN stress. Dynamic expression analysis showed that these differentially expressed genes (DEGs) differed between the two barley genotypes in response to LN stress.Conclusion: It is the first genome-wide analysis of bHLH family genes in response to LN stress in barley. The results indicate the distinct difference among HvbHLH genes in response to various abiotic stresses. The HvbHLHs specifically expressed in the LN-tolerant barley genotype XZ149 identified herein may be valuable for future function analysis of HvbHLH genes under LN stress and breeding for barley cultivars with LN tolerance.