The Gene Function Research Of PtrHox 14 And PtrHox52

Homeodomain-leucine zipper (HD-Zip) genes are the most abundant group of homeodomain HD gene in plant, and The HD-Zip family of transcription factor is unique to the plant kingdom. They can be classified into four subfamilies, according to a set of distinctive features that include DNA binding specificities, gene structures, additional common motifs and physiological functions. Arabidopsis HD-ZIP I genes are critical to plant embryogenesis and de-etiolation, and are responsive to sugar signaling, abscisic acid (ABA) signaling and abiotic stresses. The HD-Zip I genes in rice and maize were also identified to be involved in abiotic stress. In Populus trichocarpa, paralogous pairs PtrHox14 and PtrHox52 are clade y genes of HD-Zip I. The genes, OsHox22, OsHox24, AtHB7, AtHB12, were in the same clade and they were identified to be involved in drought and salt tolerance. In this study, we did some research about PtrHoxl4 and PtrHox52, and the result are as follows:This study cloned PtrHoxl4 and PtrHox52 from Populus trichocarpa cDNA library. The recombinant pBI121-PtrHox14-GFP fused gene and pBI121-PtrHox52-GFP fused gene were transformed into onion epidermal cells by particle gun for subcellular location analysis, respectively. The results showed that PtrHox14 and PtrHox52 are both located in nucleus. PlantCARE and PLACE database prediction analysis suggested that there are many cis-elements which associated with stress resistance of plants in the promoter of PtrHox14 and PtrHox52, such as MBS, GARE-motif, MYCCONSENSUSAT and light responsive element, and there is ABRE in the promoter of PtrHox52. Then, we analyzed the expression patterns of PtrHox14 and PtrHox52 under abiotic stress. The Poplar were treated with 200 mM NaCl,200 mM Mannitol,200μM ABA and 100μM SA for 0 h,3 h,6 h,12 h,24 h, and the roots, stems, leaves and shoot tips were collected for qRT-PCR. We evaluated changes in the transcript levels by analyzing log2 fold change data. The transcript levels of the PtrHox14 and PtrHox52 genes markedly increased in response to NaCl, Mannitol and ABA except in the roots.Through floral dip, a method for Agrobacterium-mediated transformation of Arabidopsis thaliana, we obtained transgenic Arabidopsis thaliana with overxpression of PtrHox52. The transfomants and wild type (WT) were treated with NaCl, Mannitol and ABA. Compared with the WT plants, overexpression of PtrHoxx52 in Arabidopsis displayed enhanced tolerance to salt. We examined the cellular levels of O2- and H2O2 in different lines under salt stress by DAB and NBT in situ staining. The results showed that the level of O2- and H2O2 in transgenic line was lower than WT. Physiological index assays showed that the content of MDA in transformants was lower than WT, and the activity of SOD, POD was higher than that in WT. These resuts showed that the heterologous expression of PtrHox52 in Arabidopsis enhanced the salt tolerance.In order to obtain the Poplar with enhanced drought and salt tolerance and in-depth study the mechanism of PtrHox14 and PtrHox52, we transformed PtrHox14 and PtrHox52 into Populus ussuriensis Kom. Through the DNA and RNA test, we identified 13 and 5 transformats, respectively. Under the salt and osmotic stress, the development of root and growth of transformants were better than the wild type. The results showed that overexpression of PtrHox14 and PtrHox52 enhanced the stress tolerance.