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.

Molting process revealed by the detailed expression profiles of RXR1/RXR2 and mining the associated genes in a spider mite, Panonychus citri

Spider mites have one ecdysone receptor(EcR)and multiple retinoid X receptors(RXRs).However,the function of these RXRs in spider mite development is unknown.Here,we screened the expression dynamics of two PcRXR isoforms at 4 h intervals in the deutonymphal stage of Panonychus citri.The results showed that PcEcR had an expression pattern similar to that of PcRXR2.For PcRXR1,its expression remained at a certain high level,when there was a decrease of both PcEcR and PcRXR2.In situ hybridization showed that PcRXR2 was detected in the central nervous mass,while the ecdysteroid biosynthesis gene PcSpo was mainly expressed at the edge of the central nervous mass.RNAi-based silencing of PcRXR1 or PcRXR2 showed the same phenotype as in mites with that of silencing PcEcR.Furthermore,RNA-seq was used to mine the genes associated with the expression dynamics of PcRXR1 or PcRXR2,which revealed that the heterodimer of EcR-RXR2 in spider mites might be linked with the cell autophagy and tissue remodeling during apolysis,and RXR1 might be linked with new epicuticle and exocuticle secretion during ecdysis.Taken together,these results increase our understanding of the regulation mechanism of ecdysteroid signal pathway in spider mite development.