Comparative analyses of primary carbon metabolism in parasitic plant species

Wiese, Anna Johanna (2013-12)

Thesis (MSc)--Stellenbosch University, 2013.

ENGLISH ABSTRACT: Most terrestrial plants make use of beneficial symbiotic associations to obtain nutrients (eg. nitrogen (N) and phosphorous (P)) from fungi in exchange for photoautotrophic carbon. However, plant parasitism (defined here as the ability of certain plants to parasitize other living material) has evolved in the plant kingdom and such plants obtain some, or all, of their nutritional needs from a host, which is severely negatively impacted by the parasite. While the physiological adaptations are well studied, the underlying molecular and biochemical mechanisms of plant parasitism remain largely unknown. As a first approach, a biochemical blueprint of primary metabolites present within parasitic plant species was constructed. The metabolomes of nineteen parasitic plants, ranging from hemi- and holoparasitism to mycoheterotrophism, were profiled via gas chromatography mass spectrometry (GC MS) based technology and targeted spectrophotometric assays. Based on these analyses, three important observations were made. First, parasitic plants were severely carbon deprived, despite being successful in colonizing and exploiting their hosts. Second, the levels of organic acids participating in mitochondrial respiration decreased and certain amino acids and soluble protein content increased. This suggests that parasitic plants utilize alternative respiratory substrates to compensate for a limitation in carbon supply. Third, although characterized by reduced carbohydrate pools, minor sugars normally not associated with plant metabolism, dominated the soluble sugar pool. The presence and significance of one of these sugars, namely turanose (α-D-glucopyranosyl-(1→3)-α-D-fructofuranose), was further investigated. Turanose biosynthetic reactions could be demonstrated in Orobanche minor extracts. Protein purification and mass spectrometry identification suggested that turanose biosynthesis occurred uniquely in parasitic plants. Future work will elucidate the functional significance of turanose metabolism in plant parasitism. Taken together, this study significantly contributes to our understanding of plant parasitism through development of metabolic signatures associated with distinct parasitic classes. These biochemical profiles highlighted several important strategies and alternative metabolic pathways that are either expressed or constitutively activated during parasitism. This knowledge broadens the scope of using parasitic plants in several biotechnological applications or as a novel research tool to address fundamental questions in plant science.

AFRIKAANSE OPSOMMING: Meeste landelike plante maak gebruik van voordelige simbiotiese assosiasies met swamme om voedinsgtowwe (bv. stikstof (N) en fosfor (P)) van hulle te verkry in ruil vir koolstof geproduseer deur die plant. Plant parasitisme (gedefinieer hier as die vermoë van sekere plante om ander lewende materiaal te parasiteer) het ontwikkel in die planteryk waar hulle sommige, of al hul voedings stowwe van 'n gasheer plant ontvang, wat erg negatief geraak word deur die parasiet. Terwyl die fisiologiese aanpassings goed gebestudeer is, is die onderliggende molekulêre en biochemiese meganismes van plant parasitisme steeds grootliks onbekend. As 'n eerste benadering, was hierdie projek geïnisieer om 'n biochemiese bloudruk op te bou van primêre metaboliete teenwoordig in parasitiese plante. Die metabolome van negentien parasitiese spesies, wat wissel van hemi - en holoparasiete tot mikoheterotrofiese plante, is ondersoek deur gas chromatografie – massa spektrometrie (GC MS) gebaseerde tegnologie en geteikende spektrofotometriese toetse. Gebaseer op hierdie ontledings was drie belangrike waarnemings gemaak. Eerstens, parasitiese plante was erg koolstof arm, ten spyte daarvan dat hulle suksesvol is in die aanhegting en ontginning van voedingstowwe vanaf gasheer plante. Tweedens, die vlakke van organiese sure wat deelneem aan mitochondriale respirasie het afgeneem, terwyl sekere aminosure en oplosbare proteïen inhoude toegeneem het. Dit dui daarop dat parasitiese plante gebruik maak van alternatiewe respiratoriese substrate om te vergoed vir 'n beperking in koolstof aanbod. Derde, alhoewel parasitiese plante gekenmerk word deur verminderde koolhidraat inhoude, het skaarse suikers wat normaalweg nie verband hou met plant metabolisme nie, hulle oplosbare suiker inhoud oorheers. Die teenwoordigheid en betekenis van een van hierdie suikers, naamlik turanose (α -D -glucopyranosyl-(1→3)-α-D-fructofuranose), was verder ondersoek. Die sintese reaksie van turanose kan gedemonstreer word in Orobanche hederae uittreksels. Proteïen suiwering en massa spektrometrie identifikasie het voorgestel dat turanose biosintese uniek plaasvind in parasitiese plante. Toekomstige werk sal aandui wat die betekenis is van turanose metabolisme in plant parasitisme. Saamgevat het hierdie studie aansienlik bygedra tot ons begrip van plant parasitisme deur ontwikkeling van metaboliese handtekeninge wat verband hou met onderskeie parasitiese klasse. Hierdie biochemiese profiele beklemtoon verskeie belangrike strategieë en alternatiewe metaboliese paaie wat óf uitgedruk of konstitutief geaktiveer word tydens parasitisme. Hierdie kennis verbreed die omvang van die gebruik van parasitiese plante in verskeie biotegnologiese toepassings of as 'n nuwe navorsings instrument om fundamentele vrae in plant wetenskap aan te spreek.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/85740
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