Abstract
Abiotic stresses such as, drought, heat, salinity, and flooding threaten global food security. Crop genetic improvement with increased resilience to abiotic stresses is a critical component of crop breeding strategies. Wheat is an important cereal crop and a staple food source globally. Enhanced drought tolerance in wheat is critical for sustainable food production and global food security. Recent advances in drought tolerance research have uncovered many key genes and transcription regulators governing morpho-physiological traits. Genes controlling root architecture and stomatal development play an important role in soil moisture extraction and its retention, and therefore have been targets of molecular breeding strategies for improving drought tolerance. In this systematic review, we have summarized evidence of beneficial contributions of root and stomatal traits to plant adaptation to drought stress. Specifically, we discuss a few key genes such as, DRO1 in rice and ERECTA in Arabidopsis and rice that were identified to be the enhancers of drought tolerance via regulation of root traits and transpiration efficiency. Additionally, we highlight several transcription factor families, such as, ERF (ethylene response factors), DREB (dehydration responsive element binding), ZFP (zinc finger proteins), WRKY, and MYB that were identified to be both positive and negative regulators of drought responses in wheat, rice, maize, and/or Arabidopsis. The overall aim of this review is to provide an overview of candidate genes that have been identified as regulators of drought response in plants. The lack of a reference genome sequence for wheat and non-transgenic approaches for manipulation of gene functions in wheat in the past had impeded high-resolution interrogation of functional elements, including genes and QTLs, and their application in cultivar improvement. The recent developments in wheat genomics and reverse genetics, including the availability of a gold-standard reference genome sequence and advent of genome editing technologies, are expected to aid in deciphering of the functional roles of genes and regulatory networks underlying adaptive phenological traits, and utilizing the outcomes of such studies in developing drought tolerant cultivars.
Highlights
Wheat is one of the important staple food crops supplying 20% of calories globally (Lobell and Gourdji, 2012; Shiferaw et al, 2013)
Crop growth and development are greatly affected by changes in morphological and physiological responses resulting from the lack of soil moisture
The drought tolerance mechanisms have been extensively studied in other model species and crop plants, including Arabidopsis, rice, and maize
Summary
Wheat is one of the important staple food crops supplying 20% of calories globally (Lobell and Gourdji, 2012; Shiferaw et al, 2013). Wheat crop is sensitive to heat and drought stresses mainly at the flowering and grain development stages, which negatively impact the yield and grain quality (lower 1,000 grain weight and change in protein quality). Demand for wheat is estimated to increase by 60% by 2050, but production might go down by 29% as a result of climate change imposed environmental stresses (Manickavelu et al, 2012). These predictions indicate that improving abiotic stress tolerance in wheat is paramount for global food security in the near future. Continued wheat genetic improvement is critically important as it has direct impact on economic development, food security, and international grain trade
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