Discovery of miRNAs and Development of Heat-Responsive miRNA-SSR Markers for Characterization of Wheat Germplasm for Terminal Heat Tolerance Breeding

A large proportion of the Asian population fulfills their energy requirements from wheat (Triticum aestivum L.). Wheat quality and yield are critically affected by the terminal heat stress across the globe. It affects approximately 40% of the wheat-cultivating regions of the world. Therefore, there is a critical need to develop improved terminal heat-tolerant wheat varieties. Marker-assisted breeding with genic simple sequence repeats (SSR) markers have been used for developing terminal heat-tolerant wheat varieties; however, only few studies involved the use of microRNA (miRNA)-based SSR markers (miRNASSRs) in wheat, which were found as key players in various abiotic stresses. In the present study, we identified 104 heat-stress-responsive miRNAs reported in various crops. Out of these, 70 miRNA-SSR markers have been validated on a set of 20 terminal heat-tolerant and heat-susceptible wheat genotypes. Among these, only 19 miRNA-SSR markers were found to be polymorphic, which were further used to study the genetic diversity and population structure. The polymorphic miRNA-SSRs amplified 61 SSR loci with an average of 2.9 alleles per locus. The polymorphic information content (PIC) value of polymorphic miRNA-SSRs ranged from 0.10 to 0.87 with a mean value of 0.48. The dendrogram constructed using unweighted neighbor-joining method and population structure analysis clustered these 20 wheat genotypes into 3 clusters. The target genes of these miRNAs are involved either directly or indirectly in providing tolerance to heat stress. Furthermore, two polymorphic markers miR159c and miR165b were declared as very promising diagnostic markers, since these markers showed specific alleles and discriminated terminal heat-tolerant genotypes from the susceptible genotypes. Thus, these identified miRNA-SSR markers will prove useful in the characterization of wheat germplasm through the study of genetic diversity and population structural analysis and in wheat molecular breeding programs aimed at terminal heat tolerance of wheat varieties

Morphological, Physiological, Biochemical and Molecular Response of Barley (H. Vulgare L.) to Water Deficiency

Barley (Hordeum vulgare L.) is one of the earliest cultivated cereals and a foundational crop of ancient agriculture. After rice, maize, and wheat, barley is the fourth most widely cultivated cereal crop in the world. It is cultivated in numerous developed and developing nations, where it frequently faces severe drought stress. Every year, droughts afflict the entire planet, frequently with catastrophic effects on crop production. Many crop modification projects have primarily targeted on the enhancement of drought resistance. However, progress toward this objective has been modest due to complexity of the trait, variability and unpredictability of the drought conditions in the field, and diversified drought tolerance mechanisms employed by plants. Barley is regarded as the most drought-resistant grain crop. It serves as an uncomplicated genetic model for studying drought tolerance mechanisms along with the associated agronomic and physiological traits. Several morphological, physiological, biochemical, molecular and quality traits were identified from various barley varieties and used to improve performance under drought stress. The present report is a comprehensive review that intends to give morphological, physiological, biochemical and genomic insights into the modulation of drought stress responses in barley and provide a thorough picture of drought tolerance mechanism