No abstract

We report the efficacy of an aldose reductase (ALDRXV4) enzyme from Xerophyta viscosa Baker in enhancing the prospects of plant's survival under abiotic stress. Transgenic tobacco plants overexpressing ALDRXV4 cDNA showed alleviation of NaCl and mannitol-induced abiotic stress. The transgenic plants survived longer periods of water deficiency and salinity stress and exhibited improved recovery after rehydration as compared to the wild type plants. The increased synthesis of aldose reductase in transgenic plants correlated with reduced methylglyoxal and malondialdehyde accumulation and an elevated level of sorbitol under stress conditions. In addition, the transgenic lines showed better photosynthetic efficiency, less electrolyte damage, greater water retention, higher proline accumulation, and favorable ionic balance under stress conditions. Together, these findings suggest the potential of engineering aldose reductase levels for better performance of crop plants growing under drought and salt stress conditions.

Despite the advances in transgenesis, transformation technologies still rely on the introduction of a selectable marker gene to identify cells and tissues that have integrated the gene of interest in their genome. The continuous presence of the marker genes in the transgenics is often controversial as it can potentially have multiple undesirable impacts. The present study employed the self-excising Cre-loxP system to generate marker-free Arabidopsis thaliana expressing the agronomically important glyoxalase I (glyI) gene from Brassica juncea to confer salt stress tolerance. A binary vector was constructed wherein the salt-inducible rd29A promoter was used to drive the expression of the glyI gene and the transformants of A. thaliana were recovered using kanamycin resistance as the selectable marker. The neomycin phosphotransferase II (nptII) gene was flanked by the loxP sites followed by the introduction of a heatinducible Cre-recombinase in between the loxP sites. The kanamycin-resistant transgenic lines of A. thaliana using this vector showed an ability to withstand stress imposed by 150 mM NaCl. The exposure of the T2 transgenic lines to a mild heat shock (37°C) resulted in the recovery of salt-tolerant, kanamycinsensitive T3 progeny. Molecular analyses of the T3 transgenic lines following the heat shock treatment confirmed the excision of the nptII gene and the completion of their life cycle in the presence of 150 mM NaCl-induced stress.

The floral meristem identity gene LEAFY (LFY) from Arabidopsis thaliana (L.) Heynh. can accelerate flowering in dicotyledonous plants. In this report, we raised transgenic plants of Brassica juncea (L.) Czern. cv. Varuna carrying the LEAFY gene (LFY) in sense and antisense orientation and studied the effect of modulation of LFY expression on flowering. The time required for the initiation of flowering was found to be reduced by 19% (∼1 wk earlier) in the transgenic plants overexpressing LFY as compared with the wild‐type untransformed control plants. Moreover, no significant yield penalty was observed in these transgenic plants. Altogether, these results open up the possibility of manipulating the flowering time in B. juncea without significant yield penalty or abnormalities.

A LEAFY cDNA was cloned from the short-day (SD) plant Brassica juncea cv Varuna. (BjLFY) consists of 1261 bp encoding for a protein of 420 amino acids and an estimated isoelectric point of 6.8. The deduced amino acid showed 99% and 86% identity to Arabidopsis thaliana and Brassica oleracea LFY cDNA respectively. The LFY transcript was detected throughout the vegetative and reproductive phase but an increase in transcript level was observed during transition. The earlier induction of BjLFY was observed in early flowering variety of B. juncea as compared to late flowering varieties further proving the critical role LEAFY plays in floral transition.