Richard J. McAvoy

The cauliflower mosaic virus (CaMV) 35S promoter sequence alters the level and patterns of activity of adjacent tissue- and organ-specific gene promoters

Here we report the effect of the 35S promoter sequence on activities of the tissue- and organ-specific gene promoters in tobacco plants. In the absence of the 35S promoter sequence the AAP2 promoter is active only in vascular tissues as indicated by expression of the AAP2:GUS gene. With the 35S promoter sequence in the same T-plasmid, transgenic plants exhibit twofold to fivefold increase in AAP2 promoter activity and the promoter becomes active in all tissue types. Transgenic plants hosting the ovary-specific AGL5:iaaM gene (iaaM coding an auxin biosynthetic gene) showed a wild-type phenotype except production of seedless fruits, whereas plants hosting the AGL5:iaaM gene along with the 35S promoter sequence showed drastic morphological alterations. RT-PCR analysis confirms that the phenotype was caused by activation of the AGL5:iaaM gene in non-ovary organs including roots, stems and flowers. When the pollen-, ovule- and early embryo-specific PAB5:barnase gene (barnase coding a RNase gene) was transformed, the presence of 35S promoter sequence drastically reduced transformation efficiencies. However, the transformation efficiencies were restored in the absence of 35S promoter, indicating that the 35S promoter might activate the expression of PAB5:barnase in non-reproductive organs such as calli and shoot primordia. Furthermore, if the 35S promoter sequence was replaced with the NOS promoter sequence, no alteration in AAP2, AGL5 or PAB5 promoter activities was observed. Our results demonstrate that the 35S promoter sequence can convert an adjacent tissue- and organ-specific gene promoter into a globally active promoter.

The maize Knotted1 gene is an effective positive selectable marker gene for Agrobacterium-mediated tobacco transformation

We have assessed the use of a homeobox gene knotted1 (kn1) from maize as a selectable marker gene for plant transformation. The kn1 gene under the control of cauliflower mosaic virus 35S promoter (35S::kn1) was introduced into Nicotiana tabacum cv. Xanthi via Agrobacterium-mediated transformation. Under nonselective conditions (without antibiotic selection) on a hormone-free medium (MS), a large number of transgenic calli and shoots were obtained from explants that were infected with Agrobacterium tumefaciens LBA4404 harboring the 35S::kn1 gene. On the other hand, no calli or shoots were produced from explants that were infected with an Agrobacterium strain harboring pBI121 (nptII selection) or from uninfected controls cultured under identical conditions. Relative to kanamycin selection conferred by nptII, the use of kn1 resulted in a 3-fold increase in transformation efficiency. The transgenic status of shoots obtained was confirmed by both histochemical detection of GUS activity and molecular analysis. The results presented here suggest that kn1 gene could be used as an effective alternative selection marker with a potential to enhance plant transformation efficiency in many plant species. With kn1 gene as a selection marker gene, no antibiotic-resistance or herbicide-resistance genes are needed so that potential risks associated with the use of these traditional selection marker genes can be eliminated.

Alternative production strategies for greenhouse tomatoes using supplemental lighting

Abstract The yield response of greenhouse tomatoes ( Lycopersicon esculentum Mill. ‘Vendor’) was examined under both natural light conditions (light available from the sun) and with the addition of 6.48 moles m −2 day −1 supplemental light from a high-pressure sodium (HPS) source. Tomato crop yield significantly increased as plant population density increased when HPS lighting was employed. No significant yield increase was obtained with increased plant density under natural light conditions. Four production strategies (representing four combinations of plant density and the number of trusses produced per plant) were tested. A significant yield increase was obtained with HPS lighting relative to the unlit control for all of the production strategies used. Similar total yields were obtained regardless of the production strategy when HPS lighting was used.

Computer Simulation of a Single Truss Tomato Cropping System

ABSTRACT THE development of a computer simulation model for greenhouse tomato crop management is discussed. The management model, based on a crop production model, will determine a production schedule designed to provide a continuous yield, optimize greenhouse space utilization, and predict production rates throughout the year.

EVALUATION OF SERANGIUM PARCESETOSUM (COLEOPTERA: COCCINELLIDAE) FOR BIOLOGICAL CONTROL OF SILVERLEAF WHITEFLY, BEMISIA ARGENTIFOLII (HOMOPTERA: ALEYRODIDAE), ON POINSETTIA

Control of silverleaf whitefly (Bemisia argentifolii Bellows & Perring) on greenhouse poinsettia with biological agents has been unreliable. Serangium parcesetosum Sicard, a coccinellid predator, appears to have great potential for silverleaf whitefly control. In our study, dynamic changes in B. argentifolii populations on caged poinsettia in response to S. parcesetosum were monitored. Silverleaf whiteflies were introduced to caged poinsettias at 1 or 10 adults per plant and 6 weeks later S. parcesetosum were introduced at 0, 2 or 4 adults per plant. Within 2 weeks of Serangium release whitefly mortality increased dramatically, and for the ensuing 10 weeks whitefly levels remained at or near those observed at time of predator release. Beetle larvae were observed 2 to 10 weeks after Serangium release when prey was initially high but not when prey was initially low. Thus, whitefly control was primarily due to prolonged survival and continuous feeding of individual beetles. Our data suggest that Serangium may work well in a multiple species biological control program for whiteflies on poinsettia. However, further study is needed on multiple species interactions within the host (pest/plant) species, and on release management strategies.

Molecular Strategies for Addressing Gene Flow Problems and Their Potential Applications in Abiotic Stress Tolerant Transgenic Plants

Transgenic plant technology provides a powerful tool to improve abiotic stress tolerance of crop plants. However, introgression of stress tolerance genes into weedy relatives may increase the potential for persistence and invasiveness, resulting in undesirable ecological consequences. A variety of gene confinement strategies have been developed to reduce unwanted transgene movement. In this review, we discuss some of these strategies, such as male and female sterility, GeneSafe™, parthenocarpy, chloroplast transformation and gene deletor technologies. In the case of the gene deletor technology, all transgenes from pollen, seeds, fruits or other organs may be eliminated once the transgene functions are no longer needed at the stage when the presence of the transgene becomes a cause for ecological or public concern. The gene deletor and other technologies can be useful to reduce unintended dispersal of stress tolerance genes and thus may facilitate commercialization of transgenic crops with enhanced tolerance to abiotic stresses.

Effect of Aerial Conditions on Heat and Mass Exchange Between Plants and Air in Greenhouses

Experiments and analysis were conducted to examine the effects of aerodynamic and thermal conditions of greenhouse air on estimation of heat and mass fluxes from a uniform canopy, and the ‘aerodynamic resistance’ formulations in delineating the aerial effects by using similarity numbers or via calibration procedures. The air flow mode in greenhouses was found to be complex, variable, and largely in mixed mode. The differences of air temperature and velocity between above- and within-canopy were so significant that use of different reference values may cause different classifications of the air flow mode. It was shown that the resistance determined using similarity numbers is locally defined, must be calculated from within-canopy aerial parameters, and has no power in explaining the vertical transport processes in the air column. The aerodynamic resistance calibrated from the sensible heat flux and the temperature difference between leaves and above-canopy air was shown to be conceptually different from that determined using similarity numbers, and deficient in describing the exchange processes between plants and the greenhouse air. Differentiation between the aerial conditions within a canopy from those above the canopy was strongly recommended for future studies on greenhouse microclimate and transport processes.

Identification and characterization of histone lysine methylation modifiers in Fragaria vesca.

The diploid woodland strawberry (Fragaria vesca) is an important model for fruit crops because of several unique characteristics including the small genome size, an ethylene-independent fruit ripening process, and fruit flesh derived from receptacle tissues rather than the ovary wall which is more typical of fruiting plants. Histone methylation is an important factor in gene regulation in higher plants but little is known about its roles in fruit development. We have identified 45 SET methyltransferase, 22 JmjC demethylase and 4 LSD demethylase genes in F. vesca. The analysis of these histone modifiers in eight plant species supports the clustering of those genes into major classes consistent with their functions. We also provide evidence that whole genome duplication and dispersed duplications via retrotransposons may have played pivotal roles in the expansion of histone modifier genes in F. vesca. Furthermore, transcriptome data demonstrated that expression of some SET genes increase as the fruit develops and peaks at the turning stage. Meanwhile, we have observed that expression of those SET genes responds to cold and heat stresses. Our results indicate that regulation of histone methylation may play a critical role in fruit development as well as responses to abiotic stresses in strawberry.

Transgenics in crops.

With rapid world population growth and declining availability of fresh water and arable land, a new technology is urgently needed to enhance agricultural productivity. Recent discoveries in the field of crop transgenics clearly demonstrate the great potential of this technology for increasing food production and improving food quality while preserving the environment for future generations. In this review, we briefly discuss some of the recent achievements in crop improvement that have been made using gene transfer technology.

Elevated auxin and reduced cytokinin contents in rootstocks improve their performance and grafting success

Summary Plant grafting is an important technique for horticultural and silvicultural production. However, many rootstock plants suffer from undesirable lateral bud outgrowth, low grafting success rates or poor rooting. Here, we used a root‐predominant gene promoter (SbUGT) to drive the expression of a tryptophan‐2‐monooxygenase gene (iaaM) from Agrobacterium tumefaciens to increase auxin levels in tobacco. The transgenic plants, when used as a rootstock, displayed inhibited lateral bud outgrowth, enhanced grafting success rate and improved root initiation. However, root elongation and biomass of SbUGT::iaaM transgenic plants were reduced compared to those of wild‐type plants. In contrast, when we used this same promoter to drive CKX (a cytokinin degradation gene) expression, the transgenic tobacco plants displayed enhanced root elongation and biomass. We then made crosses between the SbUGT::CKX and SbUGT::iaaM transgenic plants. We observed that overexpression of the CKX gene neutralized the negative effects of auxin overproduction on root elongation. Also, the simultaneous expression of both the iaaM and CKX genes in rootstock did not disrupt normal growth and developmental patterns in wild‐type scions. Our results demonstrate that expression of both the iaaM and CKX genes predominantly in roots of rootstock inhibits lateral bud release from rootstock, improves grafting success rates and enhances root initiation and biomass.