Isolation and analysis of a TIR-specific promoter from poplar

WY7 is a newly identified promoter from the rubber powdery mildew pathogen that regulates exogenous gene expression in both monocots and dicots

Promoters are very important for transcriptional regulation and gene expression, and have become invaluable tools for genetic engineering. Owing to the characteristics of obligate biotrophs, molecular research into obligate biotrophic fungi is seriously lagging behind, and very few of their endogenous promoters have been developed. In this study, a WY7 fragment was predicted in the genome of Oidium heveae Steinmann using PromoterScan. Its promoter function was verified with transient transformations (Agrobacterium tumefaciens-mediated transformation, ATMT) in Nicotiana tabacum cv. Xanthi nc. The analysis of the transcription range showed that WY7 could regulate GUS expression in both monocots (Zea mays Linn and Oryza sativa L. spp. Japonica cv. Nipponbare) and dicots (N. tabacum and Hylocereus undulates Britt). The results of the quantitative detection showed that the GUS transient expression levels when regulated by WY7 was more than 11.7 times that of the CaMV 35S promoter in dicots (N. tabacum) and 5.13 times that of the ACT1 promoter in monocots (O. sativa). GUS staining was not detected in the T1 generation of the WY7-GUS transgenic N. tabacum. This showed that WY7 is an inducible promoter. The cis elements of WY7 were predicted using PlantCARE, and further experiments indicated that WY7 was a low temperature- and salt-inducible promoter. Soluble proteins produced by WY7-hpa1Xoo transgenic tobacco elicited hypersensitive responses (HR) in N. tabacum leaves. N. tabacum transformed with pBI121-WY7-hpa1Xoo exhibited enhanced resistance to the tobacco mosaic virus (TMV). The WY7 promoter has a lot of potential as a tool for plant genetic engineering. Further in-depth studies will help to better understand the transcriptional regulation mechanisms of O. heveae.

Bidirectionalization of a methyl jasmonate-inducible plant promoter

A unidirectional promoter can be transformed into a bidirectional module by artificial methods. Here we report the bidirectionalization of the methyl jasmonate (MeJA)-inducible PtDrl02 promoter derived from poplar [(Populus tomentosa × P. bolleana) × P. tomentosa] in planta. Construction of the bidirectional PtDrl02 promoter (designated as mPtDrl02) was rapidly achieved by introducing a minimal 35S promoter in the opposite orientation to the 5' end of PtDrl02. β-Glucuronidase (GUS) and green fluorescent protein (GFP) reporter genes were also interchangeably linked to the 3'-and 5'-ends of mPtDrl02 to produce GFP/mPtDrl02/GUS and GUS/mPtDrl02/GFP vectors, respectively. Using the Agrobacterium-mediated transient expression approach, we demonstrated that the mPtDrl02 module was able to drive gene (GUS and GFP) expression in both orientations simultaneously. Furthermore, the cooperative and concurrent activity from both directions of the mPtDrl02 module was demonstrated following MeJA induction. To our knowledge, this is the first report of an artificial MeJA-responsive bidirectional promoter in perennial plants.

Functional identification and regulation of the PtDrl02 gene promoter from triploid white poplar

The PtDrl02 gene belongs to the TIR-NBS gene family in triploid white poplar (Populus tomentosa x P. bolleana) x P. tomentosa. Its expression pattern displays tissue-specificity, and the transcript level can be induced by wounding, methyl jasmonate (MeJA), and salicylic acid (SA). To understand the regulatory mechanism controlling PtDrl02 gene expression, we functionally characterized the PtDrl02 promoter region. Using the beta-glucuronidase as a reporter, we found that the PtDrl02 promoter directed gene expression mainly in the aerial parts of the plants and was confined to the cortex tissues of leaf veins, petioles, stems, and stem piths, showing a typical tissue-specific expression pattern. Deletion analysis revealed two positive regulatory regions (-985 to -669 and -669 to -467) responsible for the basal activity of the PtDrl02 promoter. Impressively, the sequence from -669 to -467 was shown to contain cis-element (s) responding to wounding and MeJA, while the promoter region between -244 and 0 could individually display wounding-responsiveness, and the fragment from -467 to -244 was required for SA- and NaCl-inducible expression of the PtDrl02 promoter. Additionally, it was found that the -985 to -669 sequence was the ABA-responding promoter fragment. These results suggested that the PtDrl02 promoter was modulated by multiple cis-regulatory elements in distinct and complex patterns to regulate PtDrl02 gene expression. Our study also suggested that the PtDrl02 gene 5' untranslated region, as well as a Populus WRKY transcription factor, PtWRKY1, was involved in the regulation of PtDrl02 promoter activities.

Functional analysis of 5' untranslated region of a TIR-NBS-encoding gene from triploid white poplar

Genome-wide analyses have identified a set of TIR-NBS-encoding genes in plants. However, the molecular mechanism underlying the expression of these genes is still unknown. In this study, we presented a TIR-NBS-encoding gene, PtDrl02, that displayed a low level of tissue-specific expression in a triploid white poplar [(Populus tomentosa x P. bolleana) x P. tomentosa], and analyzed the effects of the 5' untranslated region (UTR) on gene expression. The 5' UTR sequence repressed the reporter activity of beta-glucuronidase (GUS) gene under PtDrl02 promoter by 113.5-fold with a staining ratio of 2.97% in the transgenic tobacco plants. Quantitative RT-PCR assays revealed that the 5' UTR sequence decreased the transcript level of the GUS reporter gene by 13.3-fold, implying a regulatory role of 5' UTR in transcription and/or mRNA destabilization. The comparison of GUS activity with the transcript abundance indicated that the 5' UTR sequence decreased the translation efficiency of target gene by 88.3%. Additionally, the analysis of the transgenic P-985/UTRDelta/GUS plants showed that both the exon1 sequence and the leading intron within the 5' UTR region were responsible for the regulation of gene expression. Our results suggested a negative effect of the 5' UTR of PtDrl02 gene on gene expression.