Heterologous expression of Lolium perenne antifreeze protein confers chilling tolerance in tomato

Antifreeze proteins（AFP） are produced by certain plants, animals, fungi and bacteria that enable them to survive upon extremely low temperature. Perennial rye grass, Lolium perenne, was reported to possess AFP which protects them from cold environments. In the present investigation, we isolated AFP gene from L. perenne and expressed it in tomato plants to elucidate its role upon chilling stress. The T1 transgenic tomato lines were selected and subjected to molecular, biochemical and physiological analyses. Stable integration and transcription of Lp AFP in transgenic tomato plants was confirmed by Southern blot hybridization and RT-PCR, respectively. Physiological analyses under chilling conditions showed that the chilling stress induced physiological damage in wild type（WT） plants, while the transgenic plants remained healthy. Total sugar content increased gradually in both WT and transgenic plants throughout the chilling treatment. Interestingly, transgenic plants exhibited remarkable alterations in terms of relative water content（RWC） and electrolyte leakage index（ELI） than those of WT. RWC increased significantly by 3-fold and the electrolyte leakage was reduced by 2.6-fold in transgenic plants comparing with WT. Overall, this report proved that Lp AFP gene confers chilling tolerance in transgenic tomato plants and it could be a potential candidate to extrapolate the chilling tolerance on other chilling-sensitive food crops.

Antisense-Mediated Depletion of Tomato Chloroplast Omega-3 Fatty Acid Desaturase Enhances Thermal Tolerance

A chloroplast-localized tomato （Lycopersicon esculentum Mill.） ω-3 fatty acid desaturase gene （LeFADT） was isolated and characterized with regard to its sequence, response to various temperatures, and function in antisense transgenic tomato plants. The deduced amino acid sequence had four histidine-rich regions, of which three regions were highly conserved throughout the whole ω-3 fatty acid desaturasegene family. Southern blotting analysis showed that LeFAD7was encoded by a single copy gene and had two homologous genes in the tomato genome. Northern blot showed that LeFAD7 was expressed in all organs and was especially abundant in leaf tissue. Meanwhile, expression of LeFAD7 was induced by chilling stress （4 ℃）, but was inhibited by high temperature （45 ℃）, in leaves. Transgenic tomato plants were produced by integration of the antisense LeFAD7DNA under the control of a CaMV35S promoter into the genome. Antisense transgenic plants with lower 18 ： 3 content could maintain a higher maximal photochemical efficiency （Fv/Fm） and O2 evolution rate than wild-type plants. These results suggested that silence of the LeFAD7 gene alleviated high-temperature stress. There was also a correlation between the low content of 18 ： 3 resulting from silence of the LeFAD7 gene and tolerance to high-temperature stress.