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Plant growth is greatly influenced by environmental stresses including water deficit, salinity and extreme temperatures. Therefore, the identification of genes, especially regulatory ones whose expression enables plants to adapt to or to tolerate these abiotic stresses, is very essential. MYB proteins, a superfamily of transcription factors, play regulatory roles in developmental processes and in defense responses in plants. Members are characterized by a structurally conserved DNA-binding domain, i.e., the MYB domain. Thus, a factorial experiment in a randomized complete block design with three replications was carried out to investigate the effect of different levels of drought stress on the relative expression of TaMYB73 transcription factor gene using Real Time PCR method at Biotechnology Research Institute of Zabol University. The experimental treatments included durum wheat genotypes (Shabrang, Behrang, Karkheh, Aria and Dena) and drought levels (5, 10, 15, 20 and 25% of field capacity). Seedlings of genotypes
were cultured in pots and drought stress was exerted after 45 days (four to five leaves). Data analysis was performed using Ratio =2 ^-ΔΔCT and SAS software version 9.1. The results of the 2-way ANOVA for the effect of genotype, drought stress and cross-effects of drought stress on the relative expression of TaMYB73 gene and the amount of osmotic regulators (Proline and Carbohydrate) at different stress levels (20, 15, and 5% of field capacity) were significant in comparison with the normal condition (25% of field capacity) at 1% probability level. With the increase of drought stress level from 5 to 20% of crop capacity, relative to the normal level (25% crop capacity), the relative expression of TaMYB73 gene and osmotic regulators of proline and carbohydrates increased in Beharang, Karkheh and Dena genotypes. Therefore, Karkheh and Dena genotypes showed greater resistance to drought stress among the 5 genotypes studied.