Genetics of fumonisin biosynthesis and resistance to fusarium verticillioides in maize

dc.contributor.advisorViljoen, Altusen_ZA
dc.contributor.advisorRose, Lindy J. en_ZA
dc.contributor.authorVan Zyl, Karlienen_ZA
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.en_ZA
dc.date.accessioned2018-11-15T07:12:59Z
dc.date.accessioned2018-12-10T06:35:18Z
dc.date.available2018-11-15T07:12:59Z
dc.date.available2018-12-10T06:35:18Z
dc.date.issued2018-12
dc.descriptionThesis (PhDAgric)--Stellenbosch University, 2018.en_ZA
dc.description.abstractENGLISH ABSTRACT: Fusarium ear rot (FER) is a serious disease of maize (Zea mays L.) caused by the hemi- biotrophic fungus Fusarium verticillioides. The fungus also produces toxic secondary metabolites, known as fumonisins, in the grain that pose serious animal and human health risks. The role that fumonisins play during F. verticillioides infection is unclear, but they are believed to suppress host basal defence and facilitate necrotrophic proliferation. Disease severity and fumonisin contamination of maize are influenced by host and fungal genetics, and by plant stresses imposed by warm and dry climates. Resistance to F. verticillioides is quantitatively controlled and strongly influenced by the environment. No maize cultivar exists that is immune to FER and fumonisin contamination. The availability of the full genome sequences of both maize and F. verticillioides, however, makes it possible to investigate plant and fungal genetic responses during infection. A cluster of genes responsible for fumonisin biosynthesis in F. verticillioides has been identified, but its regulation is not yet well understood. Random insertional mutagenesis was thus performed to potentially identify genes governing fumonisin production. A mutant was obtained that produced significantly more fumonisins than its wild-type strain. Functional annotation of the single insertion site in the mutant strain showed that it was in a non-protein- coding area of F. verticillioides chromosome 10. The integration potentially causes transcriptional interference of the downstream gene encoding a F. verticillioides 7600 hypothetical protein (FVEG_08564). In future this gene needs to be inactivated by targeted mutagenesis to confirm its function, and the expression of fumonisin in maize grain infected by the mutant determined. Information on the expression of F. verticillioides genes in maize kernels during infection is limited. This is due to the small amount of fungal RNA produced in maize, which makes transcriptome sequencing unreliable. A targeted approach to study the expression of genes involved in fumonisin production in planta was, therefore, employed. A reverse-transcription quantitative PCR (RT-qPCR) assay was first optimized, and then used to study the relative expression of two fumonisin biosynthesis (FUM) genes in maize kernels. The expression of these genes was also correlated with fumonisins levels. A positive but non-significant correlation was obtained between FUM1 and FUM19 gene expression and fumonisin concentration. This finding was in conflict to a significantly positive correlation between FUM1 and FUM19, and fumonisin production, in vitro. The disparity could be attributed to factors affecting FUM gene expression and mycotoxin production in planta, such as host and pathogen genotype, the climate and kernel maturation. The RT-qPCR used can be a valuable tool to further investigate fungal genes expressed in maize kernels. Resistance to F. verticillioides in maize is controlled by many genes that are expressed to protect the plant from early infection, through colonization, to fumonisin production. These defence-related genes are present in both resistant and susceptible genotypes, but their induction is more rapid and stronger in resistant than susceptible plants. When transcript profiles of resistant and susceptible South African maize inbred lines were studied over a 52- day time period, genes associated with pathogen recognition and redox homeostasis were most strongly induced in the resistant than in the susceptible inbred line. During the necrotrophic phase of infection the plant responded by activating jasmonic acid/ethylene signalling and genes that modulate programmed cell death. The study provides novel insights into the upstream host recognition processes over the course of F. verticillioides infection and gene expression during the latter stages of infection.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Fusarium kopvrot (FKV) is 'n ernstige siekte van mielies (Zea mays L.) en word deur die hemi- biotrofiese swampatogeen, Fusarium verticillioides, veroorsaak. Die fungus produseer toksiese sekondêre metaboliete, bekend as fumonisiene, in die graan wat ernstige menslike en dierlike gesondheidsprobleme inhou. Die rol wat fumonisiene gedurende die infeksieproses speel is steeds onduidelik, maar daar word geglo dat dit basale verdediging kan onderdruk en nekrotrofiese proliferasie fasiliteer. Siekte-intensiteit en die hoeveelheid fumonisien opeenhoping in mielies word beïnvloed deur gasheer- en swamgenetika, en plantstres wat deur warm en droë klimaat opgelê word. Gasheerweerstand teen F. verticillioides word kwantitatief beheer en word sterk deur die omgewing beïnvloed. Tot dusver is geen kultivars ontwikkel wat teen FKV en fumonisien-opeenhoping bestand is nie. Die beskikbaarheid van die genome van beide mielies en F. verticillioides maak dit egter moontlik om plant- en swamgenetiese reaksies tydens infeksie te ondersoek. ‘n Groep gene wat vir die biosintese van fumonisiene verantwoordelik is, is geïdentifiseer, maar die regulering daarvan is nog nie goed verstaan nie. Mutagenese van F. verticillioides is dus uitgevoer om moontlike gene wat fumonisienproduksie affekteer, te identifiseer. ʼn Mutant wat aansienlik meer fumonisiene geproduseer het as die wilde tipe isolaat was verkry. Funksionele annotering van die enkele integrasie in die mutant het getoon dat dit in nie- proteïen-koderende DNS van F. verticillioides chromosoom 10 plaasgevind het. Die integrasie het moontlik transkripsionele ontwrigting van die geen stroom-af, F. verticillioides 7600 hipotetiese proteïen (FVEG_08564), veroorsaak. In die toekoms moet die funksie van die geen deur geteikende mutagenese bevestig word. Die uitdrukking van fumonisiene deur die mutant moet ook in graan getoets word. Inligting oor die uitdrukking van F. verticillioides gene in mieliepitte tydens infeksie is beperk. Dit is omdat ʼn klein hoeveelheid swam RNS in die mielies vervaardig word, wat ‘sequencing’ (basispaar-volgorde-bepaling) onuitvoerbaar maak. ʼn Gerugte metode om die uitdrukking van gene betrokke by die produksie van fumonisiene in mieliepitte is gevolg. ʼn Omgekeerde-transkripsie kwantitiewe PKR (RT-qPKR) protokol is eers geoptimaliseer, en dan gebruik om die relatiewe uitdrukking van twee F. verticillioides fumonisien biosintetiese (FUM) gene in die mieliepitte te bestudeer. Die uitdrukking van die gene was ook gekorreleer met fumonisienvlakke. Positiewe assosiasies maar geen beduidende korrelasies tussen FUM1 en FUM19 geenuitdrukking en fumonisienkonsentrasies was verkry nie. Hierdie bevindinge was in kontras met beduidende positiewe korrelasies tussen FUM1 en FUM19 tot fumonisienproduksie in vitro. Die verskil kan aan verskeie faktore toegeskryf word, wat die uitdrukking van FUM gene en die produksie van fumonisiene in die mieliepitte beïnvloed, soos gasheer- en patogeengenotipe, die klimaat en saadrypwording. RT-qPKR sal 'n waardevolle instrument wees om die uitdrukking van swamgene in die mieliepitte te ondersoek. Gasheerverdediging teen F. verticillioides in mielies word deur baie gene beheer wat uitgedruk word om die plant te beskerm teen vroeë infeksie, deur kolonisasie, tot fumonisienproduksie. Hierdie verdedigingsverwante gene is teenwoordig in beide weerstandbiedende en vatbare genotipes, maar hul induksie is vinniger en sterker in die weerstandbiedende genotipes. Toe die transkripsionele veranderinge van Suid-Afrikaanse weerstandbiedende en vatbare ingeteelde mielielyne oor 'n tydperk van 52 dae ondersoek was, was daar gevind dat gene wat verband hou met patogeenherkenning en redoks homeostase sterker geinduseer was in the weerstandbiedende mielielyn. Gedurende die nekrotrofiese fase van infeksie, het die plant gereageer deur jasmoniese suur/etileen seine te aktiveer, sowel as gene wat geprogrammeerde seldood moduleer. Die studie bied nuwe insig raakende die gasheerherkenningsprosesse deur die loop van F. verticillioides-infeksie sowel as geen-uitdrukking tydens laasgenoemde stadiums van infeksie.af_ZA
dc.description.versionDoctoralen_ZA
dc.embargo.terms2021-12-31
dc.format.extentx, 163 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/105164
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectGeneticsen_ZA
dc.subjectFumonisins -- Synthesisen_ZA
dc.subjectBiosynthesisen_ZA
dc.subjectFusarium diseases of plantsen_ZA
dc.subjectFusarium ear rot (FER)en_ZA
dc.subjectMaize (Zea mays) -- Diseases and pestsen_ZA
dc.subjectFusarium verticillioides -- Genetic resistanceen_ZA
dc.subjectFungal geneticsen_ZA
dc.subjectMaize (Zea mays) -- Effect of stress onen_ZA
dc.subjectMaize -- Effect of climatic changes onen_ZA
dc.subjectUCTDen_ZA
dc.titleGenetics of fumonisin biosynthesis and resistance to fusarium verticillioides in maizeen_ZA
dc.typeThesisen_ZA
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