Characterization of early defence responses in rust-infected sunflower

["Puccinia helianthi","Protein kinases","Plant defence","CIPK","DUF26","Chlorophyll lfluorescence","Sunflowers -- Diseases and pests","Sunflowers -- Disease and pest resistance -- Genetic aspects","Rust diseases","Thesis (Ph.D. (Plant Sciences))--University of the Free State, 2008"]

Bezuidenhout, Mariette ; ["Visser, B.","Van der Westhuizen, A. J."]

University of the Free State

Others  :  http://scholar.ufs.ac.za/xmlui/bitstream/11660/8419/1/BezuidenhoutM.pdf

瑞士|英语

来源: University of Iowa

【 摘 要 】

English: Plants are equipped with a surveillance system which enables the plant torecognize an invading pathogen. After recognition, the stress signal is conveyedthroughout the plant cell and subsequent defence responses are activated.Protein kinase genes encode proteins which play important roles in the relay ofthe initial signal. The aim of this study was to characterise some aspects of thedefence response of sunflower upon infection with P. helianthi. One such aspectwas the identification of a putative protein kinase gene from the resistantsunflower cultivar. The HaLRD15 gene showed good homology (e-value 7e-151) toa Calcineurin B-like protein kinase (CDPK). The virtual protein encoded by theHaLRD15 gene contained various phosphorylation sites and a MAPK dockingsite. These sites could lead to the protein being phosphorylated therebyconveying the stress signal throughout the plant cell. Further analyses ofHaLRD15 in different sunflower cultivars indicated that the gene was inducibleexpressed in only one resistant cultivar, even though gene copies were present inall the tested cultivars. This led to the conclusion that HaLRD15 could beessential factor needed in the defence response.Furthermore, an attempt was made to obtain putative disease resistance geneswhich are differentially expressed in sunflower after infection by using primersspecific for the nucleotide binding site of resistance genes. One such genefragment obtained was NBS6. The polypeptide sequence of NBS6 showedhomology to a hypothetical protein containing a DUF26 domain. Further analysisof NBS6 showed that the gene is up-regulated by defence response relatedchemicals such as MeJA and menadione. Literature have implicated thatreceptor-like protein kinases containing DUF26, were involved in the defenceresponses in the plant-pathogen interaction, more specifically in the response ofplants upon oxidative stress.As photosynthesis related genes were also differentially expressed, the effect ofthe leaf rust pathogen on the photosynthetic capacity of both resistant andsusceptible cultivars was investigated by using chlorophyll fluorescence. The electron transport rate of the infected resistant plants was shown to be muchlower than that of the infected susceptible plants. However the energy dissipatedas heat (NPQ) was shown to increase over time in the infected susceptibleplants. The expression of various genes such as glutathione S-transferase andthe large and small subunit of Rubisco were finally analysed. The infectedsusceptible plants were shown to have a higher down-regulation of the RbcSgene than the infected resistant plants. The higher electron transport rate of theinfected susceptible plants in combination with the low induction levels of RbcSas well as a higher induction of GST during the early intervals, led to theconclusion that the susceptible plants increase the electron transport system toproduce higher amounts of reactive oxygen species, thereby leading to the higherinduction of GST expression.