Morpho-physiological and expression analysis of drought tolerant gene in maize

Abstract

Drought is a major limitation to maize (Zea mays) production in the world. The present study was designed to investigate drought effects on morpho-physiological growth, changes in the biochemical (N, P, K) levels, identification of drought responsive gene orthologs and expression level of glutamine synthetase 2 gene in two maize cultivars i.e. Haq Nawaz (drought tolerant) and CIMMYT Pak (drought sensitive) under various developmental stages. Results revealed that drought stress significantly reduced plant height, root length, leaf length, leaf width, cob-diameter, silk length, ear length, cob length, fresh and dry biomass of maize at seedling, flowering and grain filling developmental stages and drought effect were more severe in C. Pak as compared to H. Nawaz cultivar. Chlorophyll a & b levels were more affected under drought stress condition at grain filling stage and the increase was more in C. Pak than H. Nawaz in comparison to the control conditions. Physiological parameters like proline, membrane stability index and soluble sugar contents were increased in response to drought as 23.34%, 2.67% and 18.24% in H. Nawaz and 24.09%, 9.05%, and 22.97% in C. Pak, respectively. Under drought stress the decrease in nitrogen and phosphorus content was 5.88% and 6.19% in H. Nawaz and 6.29% & 19.34% in C. Pak, respectively. Under drought stress increased level of potassium content was 5.72% & 6.77% in H. Nawaz and Cimmyt Pak, respectively. Drought responsive GS2 gene (OsGS2; LOC_Os04g56400) of rice was aligned against eight species of Poacea family to find out their orthologs. Based on computational analysis, 25 glutamine synthetase family genes were selected and their phylogeny, gene structural analysis, conserved domain and motifs analysis demonstrated that all the glutamine synthetase genes showed a conserved pattern. Furthermore, glutamine synthetase 2 (Gln2) gene was identified in maize as a drought responsive gene. Gln2 gene expression was performed through quantitative Real-Time PCR to confirm up-regulation of Gln2 under drought stress condition. The expression analysis of drought responsive gene (Gln2) was found more in H. Nawaz than C. Pak maize cultivar under drought stress. H. Nawaz cultivar has the potential to tolerate mild to moderate drought stress. It has been concluded from our findings that the screening of drought responsive parameters and expression analysis of drought responsive gene in drought tolerant genotype could be a better source to improve tolerance in maize under drought prone regions. Key words: Drought, Zea mays Glutamine Synthetase, Expression Analysis