Expression and Activity of Sorbitol Dehydrogenase in Apple
Sorbitol dehydrogenase (SDH, EC 1.1.1.14) has been identified as the primary enzyme that metabolizes sorbitol, the major phloem-transported carbohydrate in apple. Thus SDH may play a critical role in defining apple fruit set, development, and postharvest quality. We are currently examining SDH expression in fruit flesh versus seed, developing techniques to determine at what developmental times and in which tissues the isoforms might be expressed, and assessing how sorbitol availability may influence SDH expression and activity during fruit set.
starting clomid celexa and withdrawal drug cipro amoxil dose celexa panic attacks clomid metformin pcos successPawpaw Fruit Ripening and Postharvest Storage
The pawpaw [ Asimina triloba (L.) Dunal] is a promising tree fruit crop for Kentucky and the United States . Pawpaw grows wild in the mesic hardwood forests of 26 states in the eastern United States and is the largest edible fruit native to North America. This project is a collaboration with Dr. Kirk Pomper at Kentucky State University, who directs a comprehenisve program towards developing pawpaw as a new commercial tree fruit crop. The goals of our collaborative project are to fully characterize pawpaw fruit ripening, and to develop recommendations for maximizing postharvest storage life while maintaining high fruit quality. For further information on pawpaw, visit the Pawpaw Information Website
Plant Volatile Compounds and Microbial Development on Strawberry
Strawberry fruit produce a diverse group of wound volatile compounds, including aldehydes, alcohols, and esters, derived from the lipoxygenase-hydroperoxide lyase pathway. The volatile ( E)-2-hexenal, a 6-carbon aldehyde, is a major volatile product produced in response to bruising. We have determined that this volatile can influence the development of the major fungal mold on strawberry fruit, Botrytis cinerea L. or gray mold. Our current goals are to determine how bruising alters biosynthesis of the volatile compound and how the volatile interacts with the fungus.
The physiological basis for herbicide selectivity, herbicide
mode of action (including absorption, translocation, and mechanism
of action), and environmental effects on herbicide activity. Present
research areas include: 1) the effect of herbicide protectants
on enzyme activities, protein synthesis and herbicide metabolism;
2) environmental effects on herbicide efficacy and crop injury;
3) genetic variation in herbicide response and 4) interactions
between herbicides when applied as herbicide mixtures.
Understanding and modification of plant quality. Much of the
research involves alkaloid metabolism in tobacco and tall fescue.
We are looking at the enzymes, pathways and genetic regulation
of nicotine synthesis in attempts to understand limiting parameters
and techniques of modification of alkaloid amount and composition
that accumulates in the leaf. Some alkaloids in tall fescue are
the result of plant metabolism but others are formed only when
an endophytic fungus is present. The presence of the endophyte
also is associated with insect and large animal toxicity. One
project is aimed at understanding host-fungus interactions and
the chemicals involved in toxicity.
Investigating and understanding the biochemical and molecular
mechanisms of plant disease resistance. To facilitate biochemical
and molecular studies, we utilize model systems consisting of
plant cell suspension cultures and fungal pathogen derived factors
which elicit a plant's defense response. Plant genes coding for
putative defense-related proteins have recently been isolated.
Further characterization of these genes and evaluation of their
contribution to a plant's resistance response remain to be determined.
Seeds comprise 70% of the human diet world-wide and make up the bulk of the feed used to produce livestock that constitute a considerable proportion of the other 30% of our diet. On a practical level seed longevity and germination are of extreme importance to the establishment of nearly all plants and are the foundations of modern agriculture. On a fundamental level, seed germination is the stage of the life cycle when the plant undergoes a rapid transition from being most impervious (the seed), to being most susceptible (the seedling) to environmental stress. The orchestration of the switch from seed development to seed maturity and then to the germinative mode each involves a radical alteration of gene transcriptional activity. These alterations in transcriptional activity results in profound physiological changes that permit most seeds to survive dehydration to 5% moisture content, extend longevity in this dry state for considerable periods and finally undergo a fascinating alteration upon imbibition commencing with an intense metabolic activity and culminating in the completion of seed germination and the establishment of the next generation of plants. Using mutant screens followed by physiological and molecular investigations into the pathways thus uncovered, I examine how the seed thus fulfills its function as a propagule.
Production and physiology of woody perennials. The research
relates to the physiological, biochemical and molecular aspects
of growth and development in woody perennials. Specific projects
include: understanding the control of in vitro morphogenesis related
to juvenility in woody plants; the involvement of ethylene in
growth and development of woody perennials including embryogenesis,
dormancy and seed germination.
Our research program focuses on the general area of plant biochemistry and genetics and the application of biotechnology to crop improvement with particular emphasis on food, lipid and oil quality and new uses of agricultural commodities. This research involves the identification, isolation, cloning and manipulation by plant genetic engineering of agriculturally important genes. The major research thrust is the understanding and manipulation of fatty acid metabolism and triglyceride synthesis.
We are improving triglycerides of oilseeds with emphasis on soybeans for enhanced
edible and industrial quality. For improved edible quality we are changing the
ratios of the mix of vegetable oil fatty acids reducing both the saturated and
polyunsaturated fatty acid percentages with a corresponding increase in monounsaturated
fatty acids. This will result in a healthier and more stable product and eliminate
trans-fatty acid formation. For industrial uses we are tailoring the triglycerides
towards high triunsaturated fatty acid level which would make vegetable oils
much more valuable in several industrial products such as "drying oils"
as well as a superior source of w-3 fatty acids.
We are also are working toward developing oilseed oils high in epoxy fatty acids
which will greatly increase their value for a number of industrial products.
Epoxy fatty acids are examples of "oxylipins", or oxygenated products
of fatty acids. Another major thrust of this research program is the detailed
understanding of oxylipin formation in plant tissues. Most plant tissues form
a range of oxylipins. Some oxylipins are very important in the flavor and aroma
and therefore general quality of plant derived foods. Some are also important
in plant pest defense and defense signaling systems. Others we are working
with can be useful new antibiotics and for prevention of food-borne illnesses.
Mechanism and significance of post-translational modifications
in the large subunit (LS) of ribulose-1,5-bisphosphate carboxylase/oxygenase
as investigated using biochemical and molecular approaches. Specific
projects are currently targeted towards understanding the functional
significance of trimethyllysine-14 formation in the LS, and determination
of the molecular and enzymological characteristics of LS N-methyltransferase
and its interaction with the des(methyl) forms of rubisco.
A) Messenger RNA 3' end formation and post-transcriptional events in plants.
Current emphasis is on the delineation of protein interaction networks involving
plant polyadenylation factor subunits, and of the different RNA-binding activities
of these proteins. B) Expression of foreign genes in plants. Several collaborative
projects involving the expression of foreign genes in plants for particular
purposes are in progress. These projects seek to use foreign genes as tools
for analyzing biochemical and physiological phenomena in plants.
Isolation and identification of natural products, especially
volatile compounds, which contribute to host-parasite interactions.
Current studies involve characterization of compounds, including
lipoxygenase- derived volatiles, from host plants which alter
the growth and development of fungal pathogens that cause diseases
in plants and from plant-derived foods. The use of natural compounds
as alternatives to synthetic pesticides to reduce populations
of deleterious microorganisms on foods is being investigated.
My lab is interested in identifying components of regulatory
networks operating during plant embryogenesis. As a starting point,
we are isolating genes that are regulated by AGL15 (for AGAMOUS-like
15). AGL15 is a member of the MADS-domain family of regulatory
factors that is preferentially expressed during embryo development.
We will use a combination of biochemical, molecular, genetic and
structural techniques to identify genes regulated by AGL15 and
to understand how the products encoded by these genes operate
during seed development.
Molecular biology and evolution of plant symbionts. Endophytic
fungi provide natural biological control to forage, turf, and
wild grasses against nematodes, insects, and disease, but can
also be toxic to livestock and mammalian wildlife. These fungi
are seed transmissible, thus maternally inherited, and are ecologically
important for persistence of several grass hosts. Together with
the related Epichloe species, causative agents of grass choke
disease, they provide a model for the evolution of mutualism,
which we investigate with DNA sequence comparisons. We also genetically
engineer fungal endophytes for use in forage grass cultivars.
Transformation systems have been developed and genes involved
in the synthesis of toxic ergot alkaloids have been identified.
Such genes are targeted for disruption to reduce or eliminate
endophyte toxicity to livestock and wildlife.
My lab studies the functions of the ubiquitin (Ub)/26S proteasome proteolytic pathway in the developmental and stress response pathways of Arabidopsis thaliana. The Ub/26S proteasome pathway is essential for cellular housekeeping as well as regulation 1. Its housekeeping and stress-defense functions involve the proteolysis of misfolded proteins, products of mistranslation and stress-induced damage that are highly toxic for the cell and need to be detected and removed rapidly. The regulatory functions of the Ub/26S proteasome pathway are based on the conditional degradation of activator and repressor proteins of various signal transduction systems. In response to external or internal stimuli, many regulatory proteins undergo posttranslational modifications that either prevent or trigger their attachment to Ub, leading to their stabilization or accelerated degradation by the proteasome.
Problems that are studied in my lab are:
1. Developmental and environmental control of 26S proteasome abundance: The
26S proteasome is a multisubunit protease and the coordinated expression levels
of the gene set that encodes for its subunits ultimately determines the capacity
of the Ub/26S pathway to degrade both misfolded and regulatory proteins. Our
aim is to identify the cellular components that control the developmental and
tissue specific variations in the expression levels of proteasome subunits.
2. 26S proteasomal control of hormone regulation: We have identified proteasome
subunits that are needed for the responses to the hormones cytokinin and abscisic
acid 2,3. Our aim is to understand the molecular basis of these proteasome-dependent
steps in hormone regulation, by identifying the target proteins involved, as
well as the mechanisms that control their ubiquitination and delivery to the
proteasome for degradation.
Our laboratory focuses on dissecting plant RNAi and miRNA pathways for their working mechanism mainly in test tubes using plant cell-free extracts. We will develop more efficient and better-controlled gene suppression vectors for functional genomics and metabolic engineering, disease treatment, and plant improvement based on our deep understanding of RNAi and miRNA regulated gene expression mechanisms.
Population and evolutionary biology in forest trees. Current
work includes: (i) the molecular basis and population genetic
structure of chloroplast and mitochondrial DNA polymorphisms;
(ii) tests of cytonuclear disequilibrium (as well as the geographical
structure of this disequilibrium) among the three major eucaryotic
genomes (chloroplast, mitochondrial, and nuclear); (iii) spatial
patterns of organellar and nuclear genetic diversity within populations;
and (iv) molecular phylogeny. Taxa of interest include North American,
European, and Asian species of pine (Pinus), hemlock (Tsuga),
and oak (Quercus) genera.
Research on Pollutant metal accumulation and tissue partitioning in plants.
We are studying mechanisms that control Cd accumulation and tissue partitioning
in plants. About 70% intake of the pollutant metal Cd in humans is derived from
vegetable foods in the diet. Restricting accumulation of Cd in roots could significantly
reduce Cd burden in humans. We are investigating Cd transport into root cell
vacuoles, a primary site for transient and accumulated metal in this tissue.
Cd accumulation and tissue partitioning are being studied in tobacco plants
overexpressing Arabidopsis CAX genes that encode Cd/H antiporters, which are
primarily responsible for vacuolar Cd accumulation under low Cd exposure conditions
as occur in agricultural and natural environments. Studies include analysis
of Cd transport in isolated tonoplast vesicles, Cd accumulation and root/shoot
partitioning in solution cultured seedlings, and field studies conducted in
a real-world fashion.
Research on the Biochemistry and Metabolic Engineering of Plant Trichomes.
Glandular, secreting trichomes are surface structures that occur on many plants
(Annals of Botany, 93: 3-11, 2004). Principally, they produce and secrete to
aerial surfaces compounds that provide for insect and pathogen resistance. We
are studying metabolic biochemistry responsible for production of diterpenes
and sugar esters of tobacco glandular trichomes. Gene knockdown and overexpression
have been used to alter trichome exudates to enhance aphid resistance (demonstrated
in the laboratory and field), and create novel trichome exudate chemistries.
We have discovered a novel family of surface secreted proteins called phylloplanins
that inhibit disease caused by the fungus-like oomycete, Peronospora tabacina.
The Yuan laboratory is interested in studying the mechanisms of and engineering new functions for transcription factors (TFs) and metabolic enzymes such as cytochrome P450. Transcription factors are sequence-specific DNA binding proteins that interact with the promoter regions of target genes and modulate the rate of initiation of transcription. Plant pathways controlling biosynthesis of many bioactive secondary metabolites are regulated by one or more TFs. Understanding how TFs recognize specific DNA sequences and the ability to utilize the knowledge to create so called “designer TFs” will greatly facilitate many aspects of bioengineering. The desired protein functions are being generated by novel protein engineering approaches, including laboratory directed evolution, mutagenesis, and combinatorial protein synthesis. The P450 enzymes catalyze reactions for synthesis of many high value secondary metabolites in plants and are involved in drug metabolism in mammals. The P450 superfamily is one of the largest protein families, making it an ideal target for exploiting the gene sequence space by laboratory directed evolution.