Browsing by Author "Mary D. Strem"

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    The drought response of Theobroma cacao (cacao) and the regulation of genes involved in polyamine biosynthesis by drought arid other stresses
    (2008) Hanhong Bae; Moon S. Kim; Soo-Hyung Kim; Richard C. Sicher; David Lary; Mary D. Strem; Savithiry Natarajan; Bryan A. Bailey
    Drought can negatively impact pod production despite the fact that cacao production usually occurs in tropical areas having high rainfall. olyamincs (PAs) have been associated with the response of plants to drought in addition to their roles in responses to many other stresses, fhe constitutive and drought inducible expression patterns of genes encoding enzymes involved in PA biosynthesis were determined: an omi-hine decarboxylase (TcODC), an arginine decarboxylase (TcADC), an S-adenosylmethionine decarboxylase (TcSAMDC), a spermidine syn-hase (TcSPDS), and a spermine synthase (TcSPMS). Expression analysis using quantitative real-time reverse transcription-PCR (QPCR) esults showed thaf the PA biosynthesis genes were expressed in all plant tissues examined. Constitutive expression of PA biosynthesis genes vas-generallyTiighest in mature leaves and open flowers. Expression of TcODC, TcADC, and TcSAMDC was induced with the onset of drought md correlated with changes in stomatal conductance, photosynthesis, photosystem II efficiency, leaf water potential and altered emission of )lue-green fluorescence from cacao leaves. Induction of TcSAMDC in leaves was most closely correlated with changes in water potential. [Tie earliest measured responses to drought were enhanced expression of TcADC and TcSAMDC in roots along with decreases in stomatal con-luctance, photosynthesis, and photosysfim II efficiency. Elevated levels of putrescine, spermidine, and spermine were detected in cacao leaves 13 days after the onset of drought. Expression of all five PA associated transcripts was enhanced (1.5—3-fold) in response to treatment with ibscisic acid. TcODC and TcADC, were also responsive to mechanical wounding, infection by Phytophthora megakarya (a causal agent of black jod disease in cacao), the necrosis- and ethylene-inducing protein (Nepl) of Fusarium oxysporum, and flower abscission. TcSAMDC expression was resrionsive to all stresses except flower abscission. TcODC, although constiturively expressed at much lower levels than TcADC, TcSAMDC. * rcSPDS, and TcSPMS, was highly inducible by the fungal protein Nepl (135-fold) and the cacao pathogen Phytophthora megakarya (671-fold). Fhe full length cDNA for ODC was cloned and characterized. Among the genes studied, TcODC, TcADC, and TcSAMDC were most sensitive to nduction by drought in addition to other abiotic and biotic stresses. TcODC, TcADC, and TcSAMDC may share signal transduction pathways md/or the stress induced signal induction pathways may converge at these three genes leading to similar although not identical patterns of expression. It is possible altering PA levels in cacao will result in enhanced tolerance to multiple stresses including drought and disease as has been lemonslrated in other crops.
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    Trichoderma species form endophytic associations within Theobroma cacao trichomes
    (2009) Bryan A. Bailey; Mary D. Strem; Delilah WOOD
    Trichoderma species are usually considered soil organisms that colonize plant roots, sometimes forming a symbiotic relationship. Recent studies demonstrate that Trichoderma species are also capable of colonizing the above ground tissues of Theobroma cacao (cacao) in what has been characterized as an endophytic relationship. Trichoderma species can be re-isolated from surface sterilized cacao stem tissue, including the bark and xylem, the apical meristem, and to a lesser degree from leaves. SEM analysis of cacao stems colonized by strains of four Trichoderma species (Trichoderma ovalisporum-DIS 70a, Trichoderma hamatum- DIS 219b, Trichoderma koningiopsis-DIS 172ai, or Trichoderma harzianum-DIS 219f) showed a preference for surface colonization of glandular trichomes versus non-glandular trichomes. The Trichoderma strains colonized the glandular trichome tips and formed swellings resembling appresoria. Hyphae were observed emerging from the glandular trichomes on surface sterilized stems from cacao seedlings that had been inoculated with each of the four Trichoderma strains. Fungal hyphae were observed under the microscope emerging from the trichomes as soon as 6 h after their isolation from surface sterilized cacao seedling stems. Hyphae were also observed, in some cases, emerging from stalk cells opposite the trichome head. Repeated single trichome/hyphae isolations verified that the emerging hyphae were the Trichoderma strains with which the cacao seedlings had been inoculated. Strains of four Trichoderma species were able to enter glandular trichomes during the colonization of cacao stems where they survived surface sterilization and could be re-isolated. The penetration of cacao trichomes may provide the entry point for Trichoderma species into the cacao stem allowing systemic colonization of this tissue.