Search

Mango (

Potatoes provide an excellent source of carbohydrates, minerals, vitamins, carotenoids, anthocyanins, and several other metabolites which play an important role in human nutrition. These bioactive compounds are effective in preventing diseases like cancer, diabetes, and heart-related issues. In addition to their industrial uses, potatoes are a major focus of genetic engineering programs for the modification of nutritional properties. Several important candidate genes operating in phenylpropanoid mechanism, ascorbic acid biosynthesis pathway, carbohydrate metabolism, steroidal glycoalkaloid biosynthesis pathway, and other-related metabolic steps have been cloned and characterized at the biochemical and molecular levels. Overexpression and down regulation of genes operating in these pathways has revealed important insights into improved nutritional quality. Expression of a transgene has successfully resulted in increasing carotenoids, anthocyanins, and vitamin content in transgenic tubers. Reduction in glycoalkaloid content, enzymatic browning, flesh color, and chipping quality has been achieved via modification of the genes involved in the respective biochemical pathway in potatoes. Transgenic approaches not only resulted in improved quality but also helped in understanding the biochemical and molecular mechanisms associated with the regulation of genes in these pathways. Although the commercialization of transgenic potatoes is still hindered by consumers approval and ethical restrictions, the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 system holds promise as a non-transgenic alternative for developing nutritionally enhanced potatoes.

Heat stress can seriously reduce the tuber yield of potato (Solanum tuberosum). Early maturing cultivars are usually less affected by heat than late cultivars, which is explained by the avoidance of long exposure to summer temperatures due to the short growing time of early maturing cultivars. To determine whether there are other mechanisms involved in heat tolerance of early cultivars, we conducted correlation analysis between field earliness and growth performance of 50 potato cultivars under both heat-stressed (HS, day/night 35 °C/28 °C) and control conditions (CK, day/night 22 °C/18 °C). We classified the 50 cultivars into 8 scales of earliness and grouped them into early, intermediate and late groups based on the information on field plant maturity in Canada. We found that cultivars known to be early in the field grew similar to late cultivars under heat stress in the greenhouse in terms of traits evaluated, such as chlorophyll content and plant height. Compared with late cultivars, the early cultivars did not show any sign of early maturity under heat stress conditions. The HS/CK ratios of chlorophyll content, plant height, and largest tuber weight (tuber size) were all significantly greater in early cultivars than in late cultivars. Tuber size and field earliness were negatively correlated in CK but positively correlated under heat stress. Clearly, in addition to avoidance, other mechanisms (such as pleiotropic effects of earliness genes) were involved in the better performance of early cultivars under heat stress. These results indicated that the cultivars reprogramed their plant maturity and development under heat stress.

Potatoes stored at cold temperatures undergo undesirable sweetening due to the cleavage of sucrose into reducing sugars by invertases. Although significant research has focused on vacuolar invertase (StVAC) during cold storage of potatoes, little is known about the role of alkaline/neutral invertases (StNI). We identified eight members in the NI family from the potato genome, and phylogenetic analysis suggested their probable subcellular location as plastid/mitochondria (group α) or cytosol (group β). Using three commercially important potato cultivars with known differences in cold storage responses (‘Russet Burbank’, ‘Bintje’, and ‘Shepody’), we compared the expression of the eight StNI genes to StVAC and vacuolar invertase inhibitor (StINH2) genes during harvest, and after one and five months of storage at 4 °C or 22 °C. The activity of neutral invertase (NI), soluble acid invertase activity (SAI), and the levels of reducing sugars were also determined. Tubers of ‘Russet Burbank’ displayed high transcript abundance of StNI5, high reducing sugar content and more NI activity than SAI activity. This was associated with a high level of StINH2 transcripts and low StVAC transcript levels suggesting the susceptibility of these tubers to cold-induced sweetening could be due to cytoplasmic cleavage of sucrose by NI. In ‘Bintje’, the induction of StNI5 and StVAC transcripts and NI and SAI activities indicate that sucrose degradation is carried out by both NI and SAI. In ‘Shepody’, a higher abundance of the StNI4 and StNI6 transcripts indicates different isoforms of NI are required for sucrose degradation. This study reveals significant contribution of NI in the regulation of reducing sugars and the process of cold-induced sweetening. Additional studies are needed to determine the in vivo function of NI in cold-stored potato tubers.

Sector analysis in poplar tree stems was used to shed light on cell identity, cell fate, and patterns of development within the vascular cambium., We used sector analysis to study cambium development and dynamics and to test whether fundamental developmental and functional differences exist between cambial initials as true ‘stem cells’ and more differentiated mother cells. In many higher plants, a cylindrical lateral meristem, the vascular cambium, forms along the plant axis. Most notably in stems of perennial tree species, this meristem gives rise to xylem (wood) towards the inside of the trunk and phloem (bark) towards the outside. As such, the vascular cambium is responsible for the production of most of the planet’s forest biomass, significantly contributing to the global carbon cycle. Using the bacterial uidA reporter gene in Agrobacterium-based in vivo stem transformation experiments in poplar trees, we created 379 cambium sectors that originated from the transformation of individual cells. Results from our analysis of sector frequency and patterns are consistent with the poplar cambium featuring a single layer of true cambial initials (being able to divide both anti- and periclinally). We show that initials are frequently lost from the cambium, that such cell loss rarely occurs at mother cell level, that phloem and xylem differentiation are controlled independently, and that the frequency of mother cell replenishment is not pre-determined.

Microalgal treatment of municipal wastewater has been discussed as a novel strategy for the removal of excess nutrients and metals. Additionally, a number of products can be obtained from the resulting microalgal biomass, including energy products that can be utilized within the treatment plant. However, the effectiveness of these microalgal systems can be significantly affected by the natural biota, which could consequently impact the quality of the wastewater effluent. This study evaluated the performance of two microalgal species in the removal of nutrients from non‐sterile, highly concentrated synthetic wastewater. The results showed that monocultures of Scenedesmus sp. AMDD and Chlorella sorokiniana could remove up to 60 % NH4+, and 44 and 35 % PO43‐, respectively, in a semi‐continuous cultivation mode without negatively affecting effluent quality.

A total of 88 new Arabidopsis lines with trichome variation were recovered by screening 49,200 single-seed descent T3 lines from the SK activation-tagged population and from a new 20,000-line T-DNA insertion population (called pAG). Trichome variant lines were classified into 12 distinct phenotype categories. Single or multiple T-DNA insertion sites were identified for 89% of these mutant lines. Alleles of the well-known trichome genes TRY, GL2 and TTG1 were recovered with atypical phenotype variation not reported previously. Moreover, atypical gene expression profiles were documented for two additional mutants specifying TRY and GL2 disruptions. In remaining mutants, ten lines were disrupted in genes coding for proteins not implicated in trichome development, five were disrupted in hypothetical proteins and 11 were disrupted in proteins with unknown function. The collection represents new opportunities for the plant biology community to define trichome development more precisely and to refine the function of individual trichome genes.

Regulation of secondary (woody) growth is of substantial economic and environmental interest but is poorly understood. We identified and subsequently characterized an activation-tagged poplar (Populus tremula × Populus alba) mutant with enhanced woody growth and changes in bark texture caused primarily by increased secondary phloem production. Molecular characterization of the mutation through positioning of the tag and retransformation experiments shows that the phenotype is conditioned by activation of an uncharacterized gene that encodes a novel member of the LATERAL ORGAN BOUNDARIES DOMAIN (LBD) family of transcription factors. Homology analysis showed highest similarity to an uncharacterized LBD1 gene from Arabidopsis thaliana, and we consequently named it Populus tremula × Populus alba (Pta) LBD1. Dominant-negative suppression of Pta LBD1 via translational fusion with the repressor SRDX domain caused decreased diameter growth and suppressed and highly irregular phloem development. In wild-type plants, LBD1 was most highly expressed in the phloem and cambial zone. Two key Class I KNOTTED1-like homeobox genes that promote meristem identity in the cambium were downregulated, while an Altered Phloem Development gene that is known to promote phloem differentiation was upregulated in the mutant. A set of four LBD genes, including the LBD1 gene, was predominantly expressed in wood-forming tissues, suggesting a broader regulatory role of these transcription factors during secondary woody growth in poplar.

Trichomes are specialized epidermal cells that generally play a role in reducing transpiration and act as a deterrent to herbivory. In a screen of activation-tagged Populus tremula × Populus alba 717-1B4 trees, we identified a mutant line, fuzzy, with increased foliar trichome density. This mutant also had a 35% increase in growth rate and a 200% increase in the rate of photosynthesis as compared with wild-type poplar. The fuzzy mutant had significant resistance to feeding by larvae of the white-spotted tussock moth (Orgyia leucostigma), a generalist insect pest of poplar trees. The fuzzy trichome phenotype is attributable to activation tagging and increased expression of the gene encoding PtaMYB186, which is related to Arabidopsis thaliana MYB106, a known regulator of trichome initiation. The fuzzy phenotype can be recapitulated by overexpressing PtaMYB186 in poplar. PtaMYB186 overexpression results in reconfiguration of the poplar transcriptome, with changes in the transcript abundance of suites of genes that are related to trichome differentiation. It is notable that a plant with misexpression of a gene responsible for trichome development also had altered traits related to growth rate and pest resistance, suggesting that non-intuitive facets of plant development might be useful targets for plant improvement.

Knowledge of the functional relationship between genes and organismal phenotypes in perennial plants is extremely limited. Using a population of 627 independent events, we assessed the feasibility of activation tagging as a forward genetics tool for Populus. Mutant identification after 2 years of field testing was nearly sevenfold (6.5%) higher than in greenhouse studies that employed Arabidopsis and identical transformation vectors. Approximately two thirds of all mutant phenotypes were not seen in vitro and in the greenhouse; they were discovered only after the second year of field assessment. The trees’ large size (5-10 m in height), perennial growth, and interactions with the natural environment are factors that are thought to have contributed to the high rate of observable phenotypes in the field. The mutant phenotypes affected a variety of morphological and physiological traits, including leaf size and morphology, crown architecture, stature, vegetative dormancy, and tropic responses. Characterization of the insertion in more than 100 events with and without mutant phenotypes showed that tags predominantly (70%) inserted in a 13-Kbp region up- and downstream of the genes’ coding regions with approximately even distribution among the 19 chromosomes. Transcriptional activation was observed in many proximal genes studied. Successful phenotype recapitulation was observed in 10 of 12 retransformed genes tested, indicating true tagging and a functional relationship between the genes and observed phenotypes for most activation lines. Our studies indicate that in addition to associating mapping and QTL approaches, activation tagging can be used successfully as an effective forward gene discovery tool in Populus.

The single-celled trichome of Arabidopsis thaliana is a widely used model system for studying cell development. While the pathways that control the later stages of trichome development are well characterized, the early signalling events that co-ordinate these pathways are less well understood. Hormones such as gibberellic acid, salicylic acid, cytokinins, and ethylene are known to affect trichome initiation and development. To understand the role of the plant hormone ethylene in trichome development, an Arabidopsis loss-of-function ethylene receptor mutant, etr2-3, which has completely unbranched trichomes, is analysed in this study. It was hypothesized that ETR2 might affect the assembly of the microtubule cytoskeleton based on analysis of the cytoskeleton in developing trichomes, and exposures to paclitaxol and oryzalin, which respectively act either to stabilize or depolymerize the cytoskeleton. Through epistatic and gene expression analyses it is shown that ETR2 is positioned upstream of CHROMATIN ASSEMBLY FACTOR1 and TRYPTICHON and is independent of the GLABRA2 and GLABRA3 pathways. These results help extend understanding of the early events that control trichome development and identify a signalling pathway through which ethylene affects trichome branching.

Control of the levels of the plant hormone ethylene is crucial in the regulation of many developmental processes and stress responses. Ethylene production can be controlled by altering endogenous levels of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor to ethylene or by altering its conversion to ethylene. ACC is known to be irreversibly broken down by bacterial or fungal ACC deaminases (ACDs). Sequence analysis revealed two putative ACD genes encoded for in the genome of Arabidopsis thaliana (A. thaliana) and we detected ACD activity in plant extracts. Expression of one of these A. thaliana genes (AtACD1) in bacteria indicated that it had ACD activity. Moreover, transgenic plants harboring antisense constructs of the gene decreased ACD activity to 70% of wild-type (WT) levels, displayed an increased sensitivity to ACC and produced significantly more ethylene. Taken together, these results show that AtACD1 can act as a regulator of ACC levels in A. thaliana.

Ethylene is a central signalling agent in mediating plant defence against pathogens. Mutations to the ethylene receptor ETR1 have been shown to alter susceptibility of plants to mycotoxin-induced cell death. Using Fumonisin B1 (FB1) to induce cell death, we demonstrate that the receptor mutant ein4-1 has a reduced rate of necrosis, potentially due to an upregulation of ETHYLENE RESPONSE FACTOR1. Mutations in other ethylene receptors differentially affected the expression of genes in the jasmonic and salicylic acid defence pathways. Together these data indicate that ethylene receptors do not have redundant roles in mediating FB1-induced cell death.

Considerable functional genomic resources have been developed by the potato research community in the past decade, including expressed sequence tag (EST) libraries, SAGE libraries, microarrays, molecular-function maps, and mutant populations. This article reviews the types, characteristics, strengths, limitations, and appropriate applications of these resources for genomic research and discusses perspectives on future directions. This wide selection of resources available to potato researchers complements efforts to sequence the entire genome and advances made in the development of saturated genetic maps. Key words: Solanum, potato, genomics, expressed sequence tag, microarray, longSAGE, data mining

We have produced the largest population of activation-tagged poplar trees to date, approximately 1800 independent lines, and report on phenotypes of interest that have been identified in tissue culture and greenhouse conditions. Activation tagging is an insertional mutagenesis technique that results in the dominant upregulation of an endogenous gene. A large-scale Agrobacterium -mediated transformation protocol was used to transform the pSKI074 activation-tagging vector into Populus tremula × Populus alba hybrid poplar. We have screened the first 1000 lines for developmental abnormalities and have a visible mutant frequency of 2.4%, with alterations in leaf and stem structure as well as overall stature. Most of the phenotypes represent new phenotypes that have not previously been identified in poplar and, in some cases, not in any other plant either. Molecular analysis of the T-DNA inserts of a subpopulation of mutant lines reveal both single and double T-DNA inserts with double inserts more common in lines with visible phenotypes. The broad range of developmental mutants identified in this pilot screen of the population reveals that it will be a valuable resource for gene discovery in poplar. The full value of this population will only be realized as we screen these lines for a wide range of phenotypes.

Improvements in methodology and transformation vectors have helped to increase the transformation efficiency and stable expression of transgenes in potato. Genetic transformation in potato has many benefits and advantages over conventional breeding methods, and potato was one of the first crops to be transformed. Potato transgenic research carried out so far has mainly focused on producing lines resistant to pathogens and modification of potato physiology. This review examines the achievements and current trends in potato transformation technology as well as the biological and practical requirements for the transformation systems. Problems with the application of genetically modified crops for agricultural practices and public concerns are also discussed.

Potato tubers under cold storage accumulate sugar, which causes browning of chips and French fries during frying. After cold storage, tubers often need to be treated under warm conditions to reduce the sugar content before frying. The gene expression profiles in these stored tubers are still largely unknown although there have been excellent reports on the molecular and physiological characteristics of cold-stored tubers. In this study, we sequenced and analyzed expressed sequence tags (ESTs) of potato tubers under different temperatures, as part of the Canadian Potato Genome Project (www.cpgp.ca). Greenhouse-grown tubers of ‘Shepody’ were used to establish cDNA libraries for EST sequencing. The cold-stored-tuber EST library (4°C, 3 months) was a normalized library, and the reconditioned-tuber EST library (4°C for 3 months, then reconditioned at 21°C for 3 days) was a standard library. ESTs were processed, clustered and assembled into high quality contiguous and unique sequences. Approximately 5,000 high quality ESTs were generated from each library. These ESTs and unigenes provide useful resources for studying the metabolic regulation and gene discovery in stored potato tubers.

This paper includes the characterization of an activation-tagged mutant named rippled leaf that displays distinctive rippled-leaf morphology. Gene expression and microscopic analysis were done to characterize the rippled leaf mutant, and transgenic overexpression lines were generated and characterized using these methods. The rippled leaf mutant was found to have an activated CYCLIN D1 (CYCD1;2), and overexpression of the gene using the 35S CaMV promoter resulted in plants with a highly similar leaf morphology. Microscopic analysis of the midvein of the rippled leaf mutant revealed that the mutant possessed significantly smaller and more numerous cortical parenchyma cells in its midvein compared with wild type. As well, in rippled leaf, the vascular tissue represented a larger proportion of the midvein. In transgenic lines, there was a similar change in cortical cell size, and an even larger proportion of the midvein was vascular tissue. In conclusion, a mutant with a leaf alteration phenotype was characterized. The CYCD1;2 gene was found to be responsible for this phenotype, and the phenotype was recapitulated using overexpression of transgenic lines. Further studies with mutants such as rippled leaf are necessary for a better understanding of cell division and its relationship to plant growth and development.

As part of a large-scale genomics project focused on understanding and improving the Shepody potato, we have increased the regeneration and transformation rates for this cultivar. Using combinations of auxins and trans-zeatin, leaf and stem explants were evaluated for callus induction and shoot formation. Several plant growth regulator combinations resulted in higher plant regeneration rates over a previous method. Using the best combination of auxin and cytokinin in combination with Agrobacterium-mediated transformation, we regenerated independent putative transformants from 59.5% of the total explants plated. We ran PCR on a sample of the plants to confirm transformation and 47.1% were nptII positive; giving a confirmed transformation rate of 28.0%.

To help develop an understanding of the genes that govern the developmental characteristics of the potato (Solanum tuberosum), as well as the genes associated with responses to specified pathogens and storage conditions, The Canadian Potato Genome Project (CPGP) carried out 5' end sequencing of regular, normalized and full-length cDNA libraries of the Shepody potato cultivar, generating over 66,600 expressed sequence tags (ESTs). Libraries sequenced represented tuber developmental stages, pathogen-challenged tubers, as well as leaf, floral developmental stages, suspension cultured cells and roots. All libraries analysed to date have contributed unique sequences, with the normalized libraries high on the list. In addition, a low molecular weight library has enhanced the 3' ends of our sequence assemblies. Using the combined assembly dataset, unique tuber developmental, cold storage and pathogen-challenged sequences have been identified. A comparison of the ESTs specific to the pathogen-challenged tuber and foliar libraries revealed minimal overlap between these libraries. Mixed assemblies using over 189,000 potato EST sequences from CPGP and The Institute for Genomics Research (TIGR) has revealed common sequences, as well as CPGP- and TIGR-unique sequences.

The regulation mechanisms of any plant–pathogen interaction are complex and dynamic. A proteomic approach is valuable in understanding regulatory networks because it deals with identifying new proteins in relation to their function and ultimately aims to unravel how their expression and modification is controlled. One of the major control mechanisms for protein activity in plant–pathogen interactions is protein phosphorylation. However, studying protein phosphorylation cascades in plants presents two major technical challenges. The first is that many of the signaling components are present at very low copy numbers, which makes them difficult to detect. The second is that they are difficult to identify because there are currently only three plants with a complete genome sequence, i.e. Arabidopsis thaliana, Populus (poplar) and Oryza sativa (rice). In this article, we review proteomic approaches to study plant–pathogen interactions in both model and non-model plants and demonstrate that current proteomic and phosphoproteomic technologies have the potential to identify new components of regulatory pathways and elucidate their functions within a cellular context.

Summary The cambial K þ content of poplar increases during the growth period in a K þ supply dependent manner. Upon K þ starvation or application of tetraethylammoniumchloride (TEA þ ), a K þ channel blocker, the aver- age vessel lumen and expansion zone area were significantly reduced. In search for the molecular basis of potassium-dependent xylogenesis in poplar, Kþ transporters homologous to those of known function in Arabidopis phloem- and xylem-physiology were isolated from a poplar wood EST library. The expression profile of three distinct Kþ channel types and one K þ transporter, Populus tremula K þ uptake transporter 1 (PtKUP1), was analysed by quantitative RT-PCR. Thereby, we found P. tremula outward rectifying K þ channel (PTORK) and P. tremula K þ channel 2 (PTK2) correlated with the seasonal wood production. K þ transporter P. tremula 1 (KPT1) was predominantly found in guard cells. Following the heterologous expres- sion in Xenopus oocytes the biophysical properties of the different channels were determined. PTORK, upon membrane de-polarization mediates potassium release. PTK2 is almost voltage independent, carrying inward Kþ flux at hyperpolarized potential and K þ release upon de-polarization. PtKUP1 was expressed in a K þ uptake-deficient Escherichia coli strain, where this K þ transporter rescued K þ -dependent growth. In order to link the different K þ transporters to the cambial activity and wood production, we compared the expression profiles to seasonal changes in the K þ content of the bark as well as xylem vessel diameter. Thereby, we found PTORK and PTK2 transcripts to follow the annual Kþ variations in poplar branches. PtKUP1 was expressed at a low level throughout the year, suggesting a housekeeping function. From these data, we conclude that Kþ channels are involved in the regulation of K þ -dependent wood production.

Plant height is an important agronomic and horticultural trait that impacts plant productivity, durability and esthetic appeal. A number of the plant hormones such as gibberellic acid (GA), auxin and ethylene have been linked to control of plant architecture and size. Reduction in GA synthesis and auxin transport result in dwarfism while ethylene may have a permissive or repressive effect on tissue growth depending upon the age of plant tissues or the environmental conditions considered. We describe here an activation-tagged mutant of Populus tremula x P. alba clone 717-1B4 identified from 2000 independent transgenic lines due to its significantly reduced growth rate and smaller leaf size. Named dwarfy, the phenotype is due to increased expression of PtaACC SYNTHASE8, which codes for an enzyme in the first committed step in the biosynthesis of ethylene. Stems of dwarfy contain fiber and vessel elements that are reduced in length while leaves contain fewer cells. These morphological differences are linked to PtaACS8 inducing different transcriptomic programs in the stem and leaf, with genes related to auxin diffusion and sensing being repressed in the stem and genes related to cell division found to be repressed in the leaves. Altogether, our study gives mechanistic insight into the genetics underpinning ethylene-induced dwarfism in a perennial model organism.

Summary Advances in elucidating the molecular processes controlling flower initiation and development have provided unique opportunities to investigate the developmental genetics of non-flowering plants. In addition to providing insights into the evolutionary aspects of seed plants, identification of genes regulating reproductive organ development in gymnosperms could help determine the level of homology with current models of flower induction and floral organ identity. Based upon this, we have searched for putative developmental regulators in conifers with amino acid sequence homology to MADS-box genes. PCR cloning using degenerate primers targeted to the MADS-box domain revealed the presence of over 27 MADS-box genes within black spruce ( Picea mariana)

Trichomes are specialized epidermal cells that generally play a role in reducing transpiration and act as a deterrent to herbivory. In a screen of activation-tagged Populus tremula × Populus alba 717-1B4 trees, we identified a mutant line, fuzzy, with increased foliar trichome density. This mutant also had a 35% increase in growth rate and a 200% increase in the rate of photosynthesis as compared with wild-type poplar. The fuzzy mutant had significant resistance to feeding by larvae of the white-spotted tussock moth (Orgyia leucostigma), a generalist insect pest of poplar trees. The fuzzy trichome phenotype is attributable to activation tagging and increased expression of the gene encoding PtaMYB186, which is related to Arabidopsis thaliana MYB106, a known regulator of trichome initiation. The fuzzy phenotype can be recapitulated by overexpressing PtaMYB186 in poplar. PtaMYB186 overexpression results in reconfiguration of the poplar transcriptome, with changes in the transcript abundance of suites of genes that are related to trichome differentiation. It is notable that a plant with misexpression of a gene responsible for trichome development also had altered traits related to growth rate and pest resistance, suggesting that non-intuitive facets of plant development might be useful targets for plant improvement.

Proper plant development is dependent on the coordination and tight control of a wide variety of different signals. In the study of the plant hormone ethylene, control of the immediate biosynthetic precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is of interest as the level of ethylene can either help or hinder plant growth during times of stress. It is known that ACC can be reversibly removed from the biosynthesis pathway through conjugation into other compounds. We recently reported that plants can also irreversibly remove ACC from ethylene production through the activity of a plant encoded ACC deaminase. Heretofore only found in bacteria, we showed that there was ACC deaminase activity in both Arabidopsis and in developing wood of poplar. Here we extend this original work and show that there is also ACC deaminase activity in tomato plants, and that this activity is regulated during tomato fruit development. Further, using an antisense construct of AtACD1 in Arabidopsis, we investigate the role of ACC deamination during salt stress. Together these studies shed light on a new level of control during ethylene production in a wide variety of plant species and during different plant developmental stages.

Background Functional genomics tools provide researchers with the ability to apply high-throughput techniques to determine the function and interaction of a diverse range of genes. Mutagenised plant populations are one such resource that facilitate gene characterisation. They allow complex physiological responses to be correlated with the expression of single genes in planta, through either reverse genetics where target genes are mutagenised to assay the affect, or through forward genetics where populations of mutant lines are screened to identify those whose phenotype diverges from wild type for a particular trait. One limitation of these types of populations is the prevalence of gene redundancy within plant genomes, which can mask the affect of individual genes. Activation or enhancer populations, which not only provide knock-out but also dominant activation mutations, can facilitate the study of such genes. Results We have developed a population of almost 50,000 activation tagged A. thaliana lines that have been archived as individual lines to the T3 generation. The population is an excellent tool for both reverse and forward genetic screens and has been used successfully to identify a number of novel mutants. Insertion site sequences have been generated and mapped for 15,507 lines to enable further application of the population, while providing a clear distribution of T-DNA insertions across the genome. The population is being screened for a number of biochemical and developmental phenotypes, provisional data identifying novel alleles and genes controlling steps in proanthocyanidin biosynthesis and trichome development is presented. Conclusion This publicly available population provides an additional tool for plant researcher's to assist with determining gene function for the many as yet uncharacterised genes annotated within the Arabidopsis genome sequence http://aafc-aac.usask.ca/FST. The presence of enhancer elements on the inserted T-DNA molecule allows both knock-out and dominant activation phenotypes to be identified for traits of interest.

Ethylene is produced in wood-forming tissues, and when applied exogenously, it has been shown to cause profound effects on the pattern and rate of wood development. However, the molecular regulation of ethylene biosynthesis during wood formation is poorly understood. We have characterised an abundant 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene (PttACO1) in the wood-forming tissues of Populus tremula (L.) x P. tremuloides (Michx). PttACO1 is primarily expressed in developing secondary xylem, and is specifically upregulated during secondary wall formation. Nevertheless, according to GC-MS analysis combined with tangential cryosectioning, the distribution of ACC was found to be fairly uniform across the cambial-region tissues. Gravitational stimulation, which causes tension wood to form on the upper side of the stem, resulted in a strong induction of PttACO1 expression and ACC oxidase activity in the tension wood-forming tissues. The ACC levels increased in parallel to the PttACO1 expression. However, the increase on the upper (tension wood) side was only minor, whereas large amounts of both ACC and its hydrolysable conjugates accumulated on the lower (opposite) side of the stem. This suggests that the relatively low level of ACC on the tension wood side is a result of its conversion to ethylene by the highly upregulated PttACO1, and the concurrent accumulation of ACC on the opposite side of the wood is because of the low PttACO1 levels. We conclude that PttACO1 and ACC oxidase activity, but not ACC availability, are important in the control of the asymmetric ethylene production within the poplar stem when tension wood is induced by gravitational stimulation.

The plant body requires the transport of various materials over large distances. Two cell types that bear a striking resemblance morphologically are the cells specialized for water transport and those responsible for the transport of oxygen: xylem and lysigenous aerenchyma, respectively. Each of these cell types undergoes programmed cell death and cellular autolysis, resulting in the production of a functional space within the plant body. The major morphological difference observed is the presence of the lignified secondary wall in water-conducting tissues. The prevalence of tubular structures in other plant tissues suggests that the ability to form spaces through cellular autolysis is a fundamental paradigm in plant development and evolution.

The cambial K+ content of poplar increases during the growth period in a K+ supply dependent manner. Upon K+ starvation or application of tetraethylammoniumchloride (TEA+), a K+ channel blocker, the average vessel lumen and expansion zone area were significantly reduced. In search for the molecular basis of potassium-dependent xylogenesis in poplar, K+ transporters homologous to those of known function in Arabidopis phloem- and xylem-physiology were isolated from a poplar wood EST library. The expression profile of three distinct K+ channel types and one K+ transporter, Populus tremula K+ uptake transporter 1 (PtKUP1), was analysed by quantitative RT-PCR. Thereby, we found P. tremula outward rectifying K+ channel (PTORK) and P. tremula K+ channel 2 (PTK2) correlated with the seasonal wood production. K+ transporter P. tremula 1 (KPT1) was predominantly found in guard cells. Following the heterologous expression in Xenopus oocytes the biophysical properties of the different channels were determined. PTORK, upon membrane de-polarization mediates potassium release. PTK2 is almost voltage independent, carrying inward K+ flux at hyperpolarized potential and K+ release upon de-polarization. PtKUP1 was expressed in a K+ uptake-deficient Escherichia coli strain, where this K+ transporter rescued K+-dependent growth. In order to link the different K+ transporters to the cambial activity and wood production, we compared the expression profiles to seasonal changes in the K+ content of the bark as well as xylem vessel diameter. Thereby, we found PTORK and PTK2 transcripts to follow the annual K+ variations in poplar branches. PtKUP1 was expressed at a low level throughout the year, suggesting a housekeeping function. From these data, we conclude that K+ channels are involved in the regulation of K+-dependent wood production.

Our understanding of the molecular controls regulating the identity of the vascular cambium and the development of secondary xylem and phloem have not yet benefited much from the use of Arabidopsis as a genetic system. Under appropriate growth conditions Arabidopsis undergoes extensive secondary growth in the hypocotyl, with the development of both a vascular and a cork cambium. The secondary xylem of the hypocotyl develops in two phases, an early phase in which only vessel elements mature and a later stage in which both vessel elements and fibres are found. During this second phase the secondary xylem of Arabidopsis closely resembles the anatomy of the wood of an angiosperm tree, and can be used to address basic questions about wood formation. The development of the vascular cambium and secondary growth in Arabidopsis hypocotyl is described and its utility as a model for wood formation in trees is considered.

The level of indole-3-acetic acid (IAA) was locally modified in cambial tissues of transgenic aspen (Populus tremula L. × Populus tremuloides Michx.). We also demonstrate the use of a linked reporter gene to visualize the expression of theiaa genes. The rate-limiting bacterial IAA-biosynthetic gene iaaM and the reporter gene for β-glucuronidase (GUS), uidA, were each fused to the cambial-region-specific Agrobacterium rhizogenes rolCpromoter and linked on the same T-DNA. In situ hybridization of theiaaM gene confirmed that histochemical analysis of GUS activity could be used to predict iaaM gene expression. Moreover, quantitative fluorometric analysis of GUS activity allowed estimation of the level of de novo production of IAA in transgenic lines carrying a single-copy insert of the iaaM,uidA T-DNA. Microscale analysis of the IAA concentration across the cambial region tissues showed an increase in IAA concentration of about 35% to 40% in the two transgenic lines, but no changes in the radial distribution pattern of IAA compared with wild-type plants. This increase did not result in any changes in the developmental pattern of cambial derivatives or the cambial growth rate, which emphasizes the importance of the radial distribution pattern of IAA in controlling the development of secondary xylem, and suggests that a moderate increase in IAA concentration does not necessarily stimulate growth.

One of the best known plant disease outbreaks of all time was the Irish potato famine of 1845 to 1847 when the late blight pathogen, Phytophthora infestens, devastated the potato crop and caused more than one million deaths in Ireland. Potatoes are still plagued by disease but luckily most countries do not depend on potato as much as they did in Ireland in the 1800s. Producing disease-free potatoes, however, has come at a huge cost. To combat major diseases, such as late blight and common scab, 64 × 106 kg of pesticides are sprayed on potato fields each year. The costs associated with these measures are not only financial; environmental costs, although less easy to quantify, are significant and include negative impacts on natural ecosystems and the contamination of groundwater, lakes, and rivers. Our search for the “perfect” potato, i.e., one that has good processing qualities and disease resistance, has gained new momentum with the emergence of genomic technologies. Through functional genomics we will ga...