Glycine betaine biosynthesis genes differentially expressed in sugarcane under water stress Glycine betaine biosynthesis genes differentially expressed in sugarcane under water stress

Abstract

BackgroundPlants have developed a wide range of strategies whichallow their survival under abiotic stresses [1]. One ofthose mechanisms is the accumulation of compatiblesolutes, which protect cell structure against damageinduced by dehydration and oxidation [2]. The accumu-lated compatible solutes may include betaines andrelated compounds such as sugars and amino acids.Understanding the action mechanism of glycine betaine(GB) and its effects on drought tolerance mechanismsmay lead to the development of cultivars adapted to dif-ferent hydric conditions. In medicinal plants, betaine issynthetized by two enzymes: choline monooxygenase(CMO), and betaine aldehyde dehydrogenase (BADH)[3]. The present study evaluated gene expression profilesof CMO and BADH genes in sugarcane leaves (Sac-charum SP) submitted to three levels of water stress(mild, moderate and severe), using DNA microarrays.MethodsSugarcane plantlets of cultivars SP83-2847 and SP90-1638,considered moderately tolerant and sensitive to waterstress, respectively, were cultivated in greenhouse for60 days in sterilized soil at 26oC with 56% of humidity.After 2 months, water stress was induced by irrigationsuppression. All leaves were collected when water contentin the soil was 10%, 50% and 75% respectively, and desig-nated as mild, moderate and severe water stress.Total RNA was extracted using Trizol Reagent (Invitro-gen, USA), according to the manufacturer’s instructionsand used to synthesize a cDNA probe which was used tohybridize nylon membranes containing CMO and BADHgenes. Membranes were hybridized, for 18h at 58°C,probe was washed out and filters were exposed to ima-ging plates (Fujifilm, Japan) for 96 hours. Images werescanned using Phosphorimager FLA3000-G (Fujifilm,Japan), and spots quantified by Array Vision (ImagingResearch, Canada). Variation in gene expression levelswas obtained by log2 of the ratio of values found for con-trol plants and plants under water stress during differenttrial periods. Northern Blot was used for validation of theresults obtained by the microarray.Results and conclusionsOur analyses showed an increase in the gene expressionlevel for BADH enzyme only under moderate and severestress for the sensitive cultivar, where differential expres-sion of the tolerant variety started at the beginning stress.No differential expression was observed for CMO at sig-nificant levels for both varieties. These results confirmBADH gene modulation under water stress and its rela-tionship with water stress tolerance.