Characterization of NtREL1, a novel root-specific gene from tobacco, and upstream promoter activity analysis in homologous and heterologous hosts

Physiological and metabolic analyses reveal the proline-mediated flowering delay mechanism in Prunus persica

Peaches are susceptible to various environmental stresses. Particularly in late spring, freezing temperatures can damage peaches and consequently, affect their productivity. Therefore, flowering delay is a prominent strategy for avoiding spring frost damage. Our previous study confirmed that treatment with 5% sodium alginate and 100 mM CaCl2 (5AG) to avoid frost damage during the blooming stage delays flowering. To reveal the flowering delay mechanism of peaches, this study systematically analyzed the modification of amino acid profiles in control and 5AG-treated peach plants at different day intervals. Our findings indicate that arginine (Arg), glutamate (Glu), and proline (Pro) levels differed between the control and 5AG-treated peach shoots throughout the phenological development of flower buds. Furthermore, two amino acids (Arg and Glu) are involved in the Pro pathway. Thus, using a computational metabolomics method, Pro biosynthesis and its characteristics, gene ontology, gene synteny, cis-regulatory elements, and gene organizations were examined to decipher the involvement of Pro metabolism in peach flowering delay. In addition, qRT-PCR analysis revealed the transcriptional regulation of Pro-related and flowering-responsive genes and their role in flowering delay. Overall, this pilot study provides new insights into the role of Pro in the flowering delay mechanisms in Prunus persica through 5AG treatment.

The root-specific NtR12 promoter-based expression of RIP increased the resistance against bacterial wilt disease in tobacco

BACKGROUND

Tobacco is an important economic crop, but the quality and yield have been severely impaired by bacterial wilt disease (BWD) caused by Ralstonia solanacearum.

METHODS AND RESULTS

Here, we describe a transgenic approach to prevent BWD in tobacco plants. A new root-specific promoter of an NtR12 gene was successfully cloned. The NtR12 promoter drove GUS reporter gene expression to a high level in roots but to less extent in stems, and no significant expression was detected in leaves. The Ribosome-inactivating proteins (RIP) gene from Momordica charantia was also cloned, and its ability to inhibit Ralstonia solanacearum was evaluated using RIP protein produced by the prokaryotic expression system. The RIP gene was constructed downstream of the NtR12 promoter and transformed into the tobacco cultivar "Cuibi No. 1" (CB-1), resulting in many descendants. The resistance against BWD was significantly improved in transgenic tobacco lines expressing NtR12::RIP.

CONCLUSION

This study confirms that the RIP gene confers resistance to BWD and the NtR12 as a new promoter for its specific expression in root and stem. Our findings pave a novel avenue for transgenic engineering to prevent the harmful impact of diseases and pests in roots and stems.

Root-preferential expression of Newcastle virus glycoproteins driven by NtREL1 promoter in tobacco hairy roots and evaluation of oral delivery in mice

Newcastle disease virus (NDV) is a lethal virus in avian species with a disastrous effect on the poultry industry. NDV is enveloped by a host-derived membrane with two glycosylated haemagglutinin-neuraminidase (HN) and Fusion (F) proteins. NDV infection usually leads to death within 2-6 days, so the preexisting antibodies provide the most critical protection for this infection. The HN and F glycoproteins are considered the main targets of the immune system. In the present study, two constructs harboring the HN or F epitopes are sub-cloned separately under the control of a root-specific promoter NtREL1 or CaMV35S (35S Cauliflower Mosaic Virus promoter) as a constitutive promoter. The recombinant vectors were transformed into the Agrobacterium tumefaciens strain LBA4404 and then introduced to tobacco (Nicotiana tabacum L.) leaf disk explants. PCR with specific primers was performed to confirm the presence of the hn and f genes in the genome of the regenerated plants. Then, the positive lines were transformed via non-recombinant A. rhizogenes (strain ATCC15834) to develop hairy roots.HN and F were expressed at 0.37% and 0.33% of TSP using the CaMV35S promoter and at 0.75% and 0.54% of TSP using the NtREL1 promoter, respectively. Furthermore, the mice fed transgenic hairy roots showed a high level of antibody responses (IgG and IgA) against rHN and rF proteins.

Cloning and functional analysis of AmDUF1517 promoter from Ammopiptanthus mongolicus

Domains of unknown function protein family 1517 (DUF1517) in Ammopiptanthus mongolicus, could be induced by abiotic stresses, whose upstream regulatory sequence might be an ideal source of abiotic-induced promoter. In this study, a 1026-bp promoter of AmDUF1517 from A. mongolicus was cloned. Five deletion fragments (Full, Q1-Q4) of different length of the AmDUF1517 promoter were fused with the β-glucuronidase (GUS) reporter and transformed into Arabidopsis thaliana. The deletion analysis showed that sequences Full, Q1 and Q3 responded well to mannitol, NaCl and 4 °C stresses, while Q2 and Q4 segments did not. The Q3 fragment (280 bp; -280 to -1 bp) showed the highest promoter activity under normal and mannitol, NaCl and 4 °C conditions. The result suggested that Q3 in the AmDUF1517 gene promoter could be a new source of induced promoters for abiotic resistance breeding in plant genetic engineering.

Genome-scale mining of root-preferential genes from maize and characterization of their promoter activity

BACKGROUND

Modification of root architecture and improvement of root resistance to stresses can increase crop productivity. Functional analyses of root-specific genes are necessary for root system improvement, and root-specific promoters enable research into the regulation of root development and genetic manipulation of root traits. Maize is an important crop species; however, little systematic mining of root-specific genes and promoters has been performed to date.

RESULTS

Genomic-scale mining based on microarray data sets followed by transcript detection resulted in the identification of 222 root-specific genes. Gene Ontology enrichment analyses revealed that these 222 root-specific genes were mainly involved in responses to chemical, biotic, and abiotic stresses. Of the 222 genes, 33 were verified by quantitative reverse transcription polymerase chain reaction, and 31 showed root-preferential activity. About 2 kb upstream 5 of the 31 identified root-preferential genes were cloned from the maize genome as putative promoters and named p8463, p5023, p1534, p8531 and p6629. GUS staining of transgenic maize-derived promoter-GUS constructs revealed that the five promoters drove GUS expression in a root-preferential manner.

CONCLUSIONS

We mined root-preferential genes and their promoters in maize and verified p8463, p5023, p1534, p8531 and p6629 as root-preferential promoters. Our research enables the identification of other tissue-specific genes and promoters in maize and other species. In addition, the five promoters may enable enhancement of target gene(s) of maize in a root-preferential manner to generate novel maize cultivars with resistance to water, fertilizer constraints, or biotic stresses.

Cell wall extensins in root-microbe interactions and root secretions

Extensins are cell wall glycoproteins, belonging to the hydroxyproline-rich glycoprotein (HRGP) family, which are involved in many biological functions, including plant growth and defence. Several reviews have described the involvement of HRGPs in plant immunity but little focus has been given specifically to cell wall extensins. Yet, a large set of recently published data indicates that extensins play an important role in plant protection, especially in root-microbe interactions. Here, we summarise the current knowledge on this topic and discuss the importance of extensins in root defence. We first provide an overview of the distribution of extensin epitopes recognised by different monoclonal antibodies among plants and discuss the relevance of some of these epitopes as markers of the root defence response. We also highlight the implication of extensins in different types of plant interactions elicited by either pathogenic or beneficial micro-organisms. We then present and discuss the specific importance of extensins in root secretions, as these glycoproteins are not only found in the cell walls but are also released into the root mucilage. Finally, we propose a model to illustrate the impact of cell wall extensin on root secretions.

Overexpression of a novel peanut NBS-LRR gene AhRRS5 enhances disease resistance to Ralstonia solanacearum in tobacco

Bacterial wilt caused by Ralstonia solanacearum is a ruinous soilborne disease affecting more than 450 plant species. Efficient control methods for this disease remain unavailable to date. This study characterized a novel nucleotide-binding site-leucine-rich repeat resistance gene AhRRS5 from peanut, which was up-regulated in both resistant and susceptible peanut cultivars in response to R. solanacearum. The product of AhRRS5 was localized in the nucleus. Furthermore, treatment with phytohormones such as salicylic acid (SA), abscisic acid (ABA), methyl jasmonate (MeJA) and ethephon (ET) increased the transcript level of AhRRS5 with diverse responses between resistant and susceptible peanuts. Abiotic stresses such as drought and cold conditions also changed AhRRS5 expression. Moreover, transient overexpression induced hypersensitive response in Nicotiana benthamiana. Overexpression of AhRRS5 significantly enhanced the resistance of heterogeneous tobacco to R. solanacearum, with diverse resistance levels in different transgenic lines. Several defence-responsive marker genes in hypersensitive response, including SA, JA and ET signals, were considerably up-regulated in the transgenic lines as compared with the wild type inoculated with R. solanacearum. Nonexpressor of pathogenesis-related gene 1 (NPR1) and non-race-specific disease resistance 1 were also up-regulated in response to the pathogen. These results indicate that AhRRS5 participates in the defence response to R. solanacearum through the crosstalk of multiple signalling pathways and the involvement of NPR1 and R gene signals for its resistance. This study may guide the resistance enhancement of peanut and other economic crops to bacterial wilt disease.