Evaluation of the stress-inducible production of choline oxidase in transgenic rice as a strategy for producing the stress-protectant glycine betaine

Abstract

Glycine betaine (GB) is a compatible solute that is also capable of stabilizing the structure and function of macromolecules. Several GB-producing transgenic rice lines were generated in which the Arthrobacter pascens choline oxidase (COX) gene, fused to a chloroplast targeting sequence (TP) was expressed under the control of an ABA-inducible promoter (SIP; stress-inducible promoter) or a ubiquitin (UBI) gene promoter that is considered to be constitutive. This comparison led to interesting observations that suggest complex regulation with respect to GB synthesis and plant growth response under stress. In spite of the use of the well-studied stress-inducible promoter, the highest level of GB accumulation (up to 2.60 micromol g(-1) DW) in the SIP lines grown under saline conditions was not as high as in the UBI lines (up to 3.12 micromol g(-1) DW). Therefore, the use of an ABA-inducible promoter was not more beneficial for de novo production of GB. Interestingly, saline growth conditions enhanced GB accumulation by up to 89% in the SIP lines, whereas up to 44% increase was seen in a UBI line. In all these cases the GB levels were many-fold below the range reported for plant species that produce GB naturally. In spite of lower GB concentrations, statistically greater levels of stress tolerance were found in SIP lines than in UBI lines, suggesting that the stress protection observed in SIP plants cannot be totally explained by the increase in the GB content.

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

“…Although the accumulation of GB was lower than in natural accumulators of GB, the transgenic rice plants showed enhanced tolerance to salt and drought stress. Improved salt tolerance was observed in COX-transgenic rice plants, which accumulated even lower amounts of GB than the CDH and COD-transgenic rice plants (Su et al 2006). Similar results were reported in chloroplasttargeted CMO-transgenic rice plants (Shirasawa et al 2006).…”

“…In some cases, beneficial effects of the transgene are masked by pleiotropic effects derived from the use of strong promoters (Cuartero et al 2006). Recently, COX expression under the stressinducible promoter (SIP) and a constitutive ubiquitin promoter (UBI) was reported in rice (Su et al 2006). UBI::COX plants produced more GB (3.12 mmol g Ϫ1 dw) than SIP::COX plants (2.60 mmol g Ϫ1 dw).…”

Toward Understanding Molecular Mechanisms of Abiotic Stress Responses in Rice

“…Manipulation of genes in the metabolic pathways is a common strategy to increase plant stress tolerance. For example, improved tolerance has been found in transgenic rice plants harboring genes involved in metabolism of compatible solutes such as proline [162,190], glycine betaine [118,147,157,163], polyamines [17,141,140], and trehalose [45,46,74].…”

“…However, it is desirable to generate plants with gene expression driven by a controllable promoter so that the gene products are not produced unless under stress conditions. So far, some reports that used a stress-inducible promoter to express foreign genes have shown increased abiotic stress tolerance with normal plant growth [140,141,162,163]. Combined with other genetic and molecular approaches, the exploitation of rice stress-responsive genes (Table 1) for engineering breeding will certainly accelerate.…”

Raising salinity tolerant rice: recent progress and future perspectives

“…Overexpression of coda gene encoding COD has been most widely attempted to develop abiotic stress tolerant transgenic plants (Hayashi et al, 1997;Alia et al, 1998;Huang et al, 2000, Sulpice et al, 2003Parvanova et al, 2004;Prasad and Pardha-Saradhi, 2004). Transgenic rice, tolerant to salt stress has also been developed by the overexpression of codA by various groups (Sakamoto et al, 1998;Mohanty et al, 2002;Su et al, 2006).…”