Promoter strength comparisons of maize shrunken 1 and alcohol dehydrogenase 1 and 2 promoters in mono- and dicotyledonous species

Tissue-specific gene expression in maize seeds during colonization by Aspergillus flavus and Fusarium verticillioides

Aspergillus flavus and Fusarium verticillioides are fungal pathogens that colonize maize kernels and produce the harmful mycotoxins aflatoxin and fumonisin, respectively. Management practice based on potential host resistance to reduce contamination by these mycotoxins has proven difficult, resulting in the need for a better understanding of the infection process by these fungi and the response of maize seeds to infection. In this study, we followed the colonization of seeds by histological methods and the transcriptional changes of two maize defence-related genes in specific seed tissues by RNA in situ hybridization. Maize kernels were inoculated with either A. flavus or F. verticillioides 21-22 days after pollination, and harvested at 4, 12, 24, 48, 72, 96 and 120 h post-inoculation. The fungi colonized all tissues of maize seed, but differed in their interactions with aleurone and germ tissues. RNA in situ hybridization showed the induction of the maize pathogenesis-related protein, maize seed (PRms) gene in the aleurone and scutellum on infection by either fungus. Transcripts of the maize sucrose synthase-encoding gene, shrunken-1 (Sh1), were observed in the embryo of non-infected kernels, but were induced on infection by each fungus in the aleurone and scutellum. By comparing histological and RNA in situ hybridization results from adjacent serial sections, we found that the transcripts of these two genes accumulated in tissue prior to the arrival of the advancing pathogens in the seeds. A knowledge of the patterns of colonization and tissue-specific gene expression in response to these fungi will be helpful in the development of resistance.

Evaluation of four phloem-specific promoters in vegetative tissues of transgenic citrus plants

'Mexican' lime (Citrus aurantifolia Swingle) was transformed with constructs that contained chimeric promoter-gus gene fusions of phloem-specific rolC promoter of Agrobacterium rhizogenes, Arabidopsis thaliana sucrose-H(+) symporter (AtSUC2) gene promoter of Arabidopsis thaliana, rice tungro bacilliform virus (RTBV) promoter and sucrose synthase l (RSs1) gene promoter of Oryza sativa (rice). Histochemical β-glucuronidase (GUS) analysis revealed vascular-specific expression of the GUS protein in citrus. The RTBV promoter was the most efficient promoter in this study while the RSs1 promoter could drive low levels of gus gene expression in citrus. These results were further validated by reverse transcription real-time polymerase chain reaction and northern blotting. Southern blot analysis confirmed stable transgene integration, which ranged from a single insertion to four copies per genome. The use of phloem-specific promoters in citrus will allow targeted transgene expression of antibacterial constructs designed to battle huanglongbing disease (HLB or citrus greening disease), associated with a phloem-limited Gram-negative bacterium.

Biolistics transformation of wheat

We present a complete, step-by-step guide to the production of transformed wheat plants using a particle bombardment device to deliver plasmid DNA into immature embryos and the regeneration of transgenic plants via somatic embryogenesis. Currently, this is the most commonly used method for transforming wheat and it offers some advantages. However, it will be interesting to see whether this position is challenged as facile methods are developed for delivering DNA by Agrobacterium tumefaciens or by the production of transformants via a germ-line process (see other chapters in this book).

Molecular genetic improvement of cereals: transgenic wheat (Triticum aestivum L.)

Only modest progress has been made in the molecular genetic improvement of wheat following the production of the first transgenic plants in 1992, made possible by the development of efficient, long-term regenerable embryogenic cultures derived from immature embryos and use of the biolistics method for the direct delivery of DNA into regenerable cells. Transgenic lines expressing genes that confer resistance to environmentally friendly non-selective herbicides, and pests and pathogens have been produced, in addition to lines with improved bread-making and nutritional qualities; some of these are ready for commercial production. Reduction of losses caused by weeds, pests and pathogens in such plants not only indirectly increases available arable land and fresh water supplies, but also conserves energy and natural resources. Nevertheless, the work carried out thus far can be considered only the beginning, as many difficult tasks lie ahead and much remains to be done. The challenge now is to produce higher-yielding varieties that are more nutritious, and are resistant or tolerant to a wide variety of biotic as well as abiotic stresses (especially drought, salinity, heavy metal toxicity) that currently cause substantial losses in productivity. How well we will meet this challenge for wheat, and indeed for other cereal and non-cereal crops, will depend largely on establishing collaborative partnerships between breeders, molecular biologists, biotechnologists and industry, and on how effectively they make use of the knowledge and insights gained from basic studies in plant biology and genetics, the sequencing of plant/cereal genomes, the discovery of synteny in cereals, and the availability of DNA-based markers and increasingly detailed chromosomal maps.

Evaluation of five promoters for use in transformation of oil palm (Elaeis guineensis Jacq.)

The efficiency of GUS (β-Glucuronidase) gene expression in embryogenic callus and young leaflets of mature and seedling palm after microprojectile bombardment with five constructs (pEmuGN, pAHC25, pAct1-F4, pGH24 and pBARGUS) was evaluated to identify the most suitable promoter(s) to use in transformation attempts in oil palm. Expression of the GUS gene driven by theEmu, Ubi1, Act1 35S orAdh1 was assayed, both histochemically and fluorometrically, from a total of 200 plates of tissues in eight independent experiments two days after bombardment. A completely randomized experimental design was used for each experiment, and the data analysed by ANOVA and Duncan's Multiple Range Test. The expression level of GUS driven by theEmu orUbi1 promoters was significantly higher than that of the Act], 35S and Adhl promoters in many experiments, and that of theAdhl was significantly lower than those of the other four promoters. Both histochemical and fluorometric data indicate that in embryogenic callus, the expression of theEmu promoter was higher than that of theUbi1 whereas in young leaflets from mature palm the Ubi1 expression was stronger. The performances of the five promoters were also tested in tobacco callus using a fluorometric GUS assay. The activity of the 35S promoter was highest, and significantly different from that of all the other promoters except theEmu, and that of theAct1 promoter was lowest. These results indicate that either theUbil orEmu promoter should facilitate the expression of desired genes in oil palm and aid in development of an efficient stable transformation system.

Phenylalanine ammonia-lyase gene structure, expression, and evolution in Nicotiana

Phenylalanine ammonia-lyase (PAL) catalyzes the first reaction in the general phenylpropanoid pathway leading to the production of phenolic compounds with a significant range of biological function. A PAL gene we designated gPAL1, cloned from tobacco, consists of two exons separated by an intron of 1932 bp. Exon I, 398 bp, and exon II, 1747 bp, together encode a polypeptide of 715 amino acids. A putative TATA box and polyadenylation signal are found 144 bp upstream of the initiation codon and 193 bp downstream from the stop codon, respectively. Using various parts of gPAL1 as probes, genomic Southern blots indicated the presence of a small family of PAL genes in the tobacco genome that can be divided into two distinct subfamilies, one consisting of pal1 and pal2 and another of pal3 and pal4. Comparative genomic blot analysis of progenitor species (Nicotiana tomentosiformis and N. sylvestris) indicated that each species contains one PAL gene from each of the subfamilies, suggesting that pal1 and pal3 (or pal2 and pal4) diverged prior to the evolution of N. tabacum. Expression of the PAL gene family was examined using RNA gel blots. PAL transcript levels were significantly higher in flowers and roots than in leaves and stems of mature plants. PAL transcripts accumulate differentially during flower and leaf maturation in that mRNA levels decline during flower maturation but increase during leaf maturation. In leaves, PAL transcripts rapidly accumulated afer wounding.

The effect of different promoter-sequences on transient expression of gus reporter gene in cultured barley (Hordeum vulgare L.) cells

The cauliflower mosaic virus 35S (35S) and the enhanced 35S (E35S) promoters fused with maize alcohol dehydrogenase (Adh1) intron1 or maize shrunken locus (sh1) intronl along with maize Adh1 and rice actin (Act1) promoters fused to their respective first introns were tested for transient expression of the E.coli β-glucuronidase (gus) reporter gene in cultured barley (Hordeum vulgare L) cells. The plasmids, carrying the respective promoterintron combinations to drive the gus fused to nopaline synthase (nos) terminator, were introduced into cultured barley cells using a particle gun. The rice Act1 promoter with its first intron gave the highest expression of all promoter intron combinations studied. This was followed by the E35S promoter and no significant differences were observed between the other two promoters tested. The rice actin promoter is now being used to drive selectable marker genes to obtain stably transformed cereal cells.

Increased gene expression by the first intron of maize shrunken-1 locus in grass species

The first intron of the shrunken-1 (Sh1) locus of maize was incorporated into constructs containing the chloramphenicol acetyltransferase gene (CAT) coupled with the nopaline synthase 3' polyadenylation signal. Transcription was driven with the 35S promoter of the cauliflower mosaic virus (CaMV) or the Sh1 promoter of maize. Transient gene expression was monitored following electroporation into protoplasts of Panicum maximum (guineagrass), Pennisetum purpureum (napiergrass), or Zea mays (maize). The 1028 base pair intron increased gene expression in cells of each species when transcription was driven with the 35S promoter. Eleven to 91-fold increases were observed. Expression levels observed in maize were two and eight times those observed in napiergrass and guineagrass, respectively. The 35S promoter gave CAT activity 10 to 100 times that observed with the Sh1 promoter. Whereas expression driven by the 35S promoter was reproducible, that observed with the Sh1 promoter proved quite variable. In similar constructs the first intron of the alcohol dehydrogenase-1 (Adh1) gene of maize led to increased gene expression of only 7 to 10% of that observed with the Sh1 first intron. The increased level of gene expression caused by the Sh1 first intron is approximately 10 times higher than that caused by any other plant introns that have been used. Thus, the Sh1 first intron may prove quite useful in increasing expression of foreign genes in monocots and possibly other plants.