Effect of drought stress on NAC gene expression in some bread wheat cultivars of Sistan region

Introduction Plant growth is severely influenced by environmental stresses such as drought, high salinity and extreme temperatures. Environmental stresses trigger a wide range of plant responses, like change in the gene expression to variability in cellular metabolism and growth. In the past years investigation on abiotic stresses, especially drought stress, has focused on plant resistance genes and their mechanism of function. This research revealed that a majority of the genes that have important roles in the biotic and abiotic stresses resistance encode transcription factors. Hence, the identification of genes especially regulatory ones whose expression enables plants to adapt to or to tolerate these abiotic stresses, is very essential. The NAC gene family is one of the types of genes related to transcription factors that is expressed in different tissues and growth stages. In a number of transcription factors effective in aging of the leaf has been identified. The transcription factors of this family are more associated with aging related genes and growth and development processes in response to stresses in many crops. The objective of this study was to investigate the tolerate of five wheat cultivars (Hamoon, Hirmand, Kavir, Boulani and Boulani Cross) under drought stress conditions (5, 10, 15, 20 and 25% Field Capacity) based on ratio of NAC gene relative expression and osmotic regulators modifications. Materials and methods A factorial experiment was carried out using a randomized complete block design (RCBD) with three replications during the 2017–2018 at Biotechnology Research Institute of Zabol University, Zabol, Sistan and Baluchestan Province, Iran. The experimental treatments included bread wheat cultivars (Hamoon, Hirmand, Kavir, Boulani and Boulani Cross) and drought stress levels (5, 10, 15, 20 and 25% Field capacity). The bread wheat cultivars were planted in pot. Drought stress was applied at seedling stage (four to five leaves). Physiological traits (such as Polyphenol oxidase and Proline) and the level of expression of the TaNAC67 gene were estimated in this experiment. Data analysis was performed using Ratio =2 -ΔΔCT and SAS software version 9.1. Results The results of analysis of variance (ANOVA) showed that, the effect of cultivar, drought stress and interaction of drought stress × cultivar on the relative expression of NAC gene and osmotic regulators at drought stress levels (20, 15, and 5% Field capacity) compared to normal levels (25% Field capacity) was significant. Based on the obtained results, increasing of drought stress severity increased studied traits. The results of simple effects of drought stress levels showed that increasing the levels of drought stress, the traits were increased, so that The highest TaNAC gene expression, Polyphenol oxidase and Proline of leaf was obtained in plants treated with drought stress 5% crop capacity. The results of this experiment showed that increasing the levels of drought stress with 20, 15, 10, 5% of the field capacity compared to the normal level of 25% of field capacity, among the five cultivars of bread wheat, the relative expression of NAC gene increased. In addition to increasing the relative expression of NAC gene in the seedling stage, Polyphenol Oxidase and proline accumulation increased in Hirmand cultivar and then Boulani Cross cultivar. Conclusion According to the findings of this experiment through the five Sistan region bread wheat cultivars, the Hirmand and then Boulani Cross cultivars indicated better response than other genotypes to drought stress. As a result, due to the coherence of the molecular results and studied traits, Hirmand cultivar had the best response under drought stress conditions. Performing more complementary experiments is mandatory to confirm the obtained results from Hirmand cultivar in this work.