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Accueil du site → Doctorat → Afrique du Sud → 2007 → CHARACTERIZATION OF SOME EARLY DEFENCE RESPONSES OF LEAF RUST‐INFECTED WHEAT

University of the Free State (2007)

CHARACTERIZATION OF SOME EARLY DEFENCE RESPONSES OF LEAF RUST‐INFECTED WHEAT

Appelgryn, Johannes Jacobus

Titre : CHARACTERIZATION OF SOME EARLY DEFENCE RESPONSES OF LEAF RUST‐INFECTED WHEAT

Auteur : Appelgryn, Johannes Jacobus

Université de soutenance : University of the Free State

Grade : Doctor of Philosophy (PhD) 2007

Résumé
The aim of this study was to investigate the early events following the infection of wheat with leaf rust. An attempt was made to identify and characterize genes putatively involved in these early events. More specifically, the aim was to obtain genes whose role in infected plants could be linked to the resistance locus within the resistant plant. DDRT‐PCR was used to isolate differentially expressed genes from the resistant Thatcher+Lr34 plants during the first 15 h after infection. Four cDNA fragments were cloned and sequenced. The first clone coded for a monosaccharide transporter, while the second clone encoded a cell wall invertase. Both these clones formed part of a different study to postulate a role for these proteins during infection. The third cDNA clone, coded for a putative heat shock protein. Heat shock proteins are molecular chaperones and are normally involved in ensuring cellular homeostasis by preventing the aggregation of denatured proteins and assisting in the folding and transport of new and denatured proteins. The fourth clone encoded an indole‐3‐glycerol phosphate lyase. The expression of the putative heat shock protein increased 86 fold within 9 h.p.i in infected resistant wheat and was chosen for further analysis. The gene shared very high sequence similarity to an O. sativa HSP70 gene and was called TaHlp01 (Triticum aestivum Heat shock Like Protein 01). TaHlp01 was inducibly expressed upon infection of resistant wheat with leaf rust as well as yellow rust but its expression remained constant in the infected susceptible cultivars. This indicated that the regulation of expression is dependent on the presence of the resistance locus within the resistant cultivars. A transient repression of TaHlp01 expression was found during the later stages of infection in both the IR and IS plants that were similar to a transient repression of TaHlp01 expression after Thatcher+Lr34 plants were treated with salicylic acid. TaHlp01 expression was also found to be induced by heat stress, indicating a possible role during heat stress. A possible interplant communication event was also examined. It was found that infected plants were able to induce the defence response of uninfected plants. This communication between infected and uninfected plants was more effective between plants of the same cultivars than between different cultivars. It appears as if resistant plants were able to induce a more controlled defence response than susceptible plants. When uninfected resistant and susceptible plants exposed to infected plants, was infected themselves, they exhibited a more resistant phenotype compared to plants that was not exposed. The communication event during this interaction most likely involves jasmonic acid.

Mots clés : •Puccinia triticina •plant defence •interplant communication •TaHlp01 •Triticum aestivum

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