Glycinebetaine accumulation is more effective in chloroplasts than in the cytosol for protecting transgenic tomato plants against abiotic stress

Abstract

Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) plants were transformed with a gene for choline oxidase (codA) from Arthrobacter globiformis. The gene product (CODA) was targeted to the chloroplasts (Chl-codA), cytosol (Cyt-codA) or both compartments simultaneously (ChlCyt-codA). These three transgenic plant types accumulated different amounts and proportions of glycinebetaine (GB) in their chloroplasts and cytosol. Targeting CODA to either the cytosol or both compartments simultaneously increased total GB content by five-to sixfold over that measured from the chloroplast targeted lines. Accumulation of GB in codA transgenic plants was tissue dependent, with the highest levels being recorded in reproductive organs. Despite accumulating, the lowest amounts of GB, Chl-codA plants exhibited equal or higher degrees of enhanced tolerance to various abiotic stresses. This suggests that chloroplastic GB is more effective than cytosolic GB in protecting plant cells against chilling, high salt and oxidative stresses. Chloroplastic GB levels were positively correlated with the degree of oxidative stress tolerance conferred, whereas cytosolic GB showed no such a correlation. Thus, an increase in total GB content does not necessarily lead to enhanced stress tolerance, but additional accumulation of chloroplastic GB is likely to further raise the level of stress tolerance beyond what we have observed.

Genetic engineering of glycine betaine biosynthesis to enhance abiotic stress tolerance in plants

“…It is possible that different plant species have different capacities for cytosolic choline biosynthesis and transport to the chloroplast for GB biosynthesis. COD-transgenic tomato plants accumulated more GB in the cytosol than the chloroplast, similar to CMO-tobacco (Park et al 2007a). This indicates that both tobacco and tomato plants are less efficient at either choline biosynthesis and/or its transport to the chloroplast.…”

“…High concentration of intracellular ROS has damaging effects on cellular components and also hinders repair of the PSII complex by inhibition of de novo protein synthesis (Nishiyama et al 2001). Park et al (2007a) suggested that one of the possible reasons for the greater protection against low-temperature stress in chloroplast-targeted CODtransgenic tomato plants might be an improved oxygenevolving ability of the PSII complex by GB-induced repair. Another reason might be that GB stabilizes membrane integrity against extreme temperatures, reduces membrane lipid peroxidation, and protects PSII electron transport Hamilton and Heckathorn 2001).…”

“…Both exogenous and endogenous application of GB enhances catalase activity and thus enhances tolerance to low-temperature stress. An increase in catalase activity was observed in the chloroplast-targeted COD-transgenic tomato plants that demonstrated enhanced tolerance to both chilling and oxidative stress (Park et al 2007a). …”

“…The enhanced chilling-stress tolerance in the presence of very low GB levels may be due to the very low threshold level of endogenous GB (Ͼ0.1 mmol g Ϫ1 fw) that is sufficient to provide full protection against chilling stress in transgenic tomato (Park et al 2004). In addition, both cytosolic and chloroplast-targeted COD-transgenic tomato plants showed a correlation between the accumulated GB in these compartments and the degree of tolerance to low temperature, salt, and oxidative stresses (Park et al 2007a). The cytosolic-targeted COD-transgenic tomato plants accumulated five-to six-fold more GB than chloroplast-targeted COD-tomato plants.…”

Role of Glycine Betaine and Potassium Nitrate in Drought Tolerance using Proline Accumulation in Rice (Oryza sativa L.)

“…in higher plants. Glycinebetaine (GB) is one such osmolyte whose association with tolerance to abiotic stresses has been supported by a number of publications (Manaf, 2016;Wang et al, 2010;Park et al,2007).The researches on manipulation of GB biosynthetic pathway by genetic transformation and exogenous application are in continuous progress. However, exogenousfoliar application of GB represents a short and simple approach for mitigating the adverse effects of stress.…”