Molecular and cellular analysis of adult plant resistance in wheat to Puccinia graminis f. sp. tritici

[摘要] Wheat (Triticum aestivum L.) production is affected by fungal diseases such as stem rustcaused by Puccinia graminis f. sp. tritici Erikss. & Henning (Pgt). Commerciallyimplemented single gene resistance in wheat may break down with the emergence of newvirulent races of Pgt. Emergence of the 'Ug99' race group reaffirmed the need for durablestem rust resistance. A paradigm shift is therefore required towards durable types ofresistance. Adult plant resistance (APR) may remain durable in the presence of new pathogenraces. A preceding project identified two Kenyan wheat lines (W1406 and W6979) from theGenome Resource Unit (Norwich, UK) that exhibited APR to Pgt. The aim of this study wasto investigate the APR response to Pgt race PTKST in W1406 and W6979 compared to asusceptible control (37-07). Four greenhouse trials were done and Pgt-inoculated flag leafsheaths were sampled at selected days post inoculation (dpi). Histological observations usingscanning electron microscopy and fluorescence microscopy, described the infection processof Pgt on wheat flag leaf sheaths. Fluorescence microscopy in particular showed a significantdecrease in Pgt colony sizes in the APR lines at 5 dpi. Fungal biomass quantification with achitin-binding probe and relative expression of the Pgt β-tubulin gene distinguished the APRlines from line 37-07 at 5 and 10 dpi. Relative expression of a haustorium-associated genealso distinguished the APR lines from the control line at 5 dpi. Taken together, these findingssupported phenotypic evidence that W1406 and W6979 inhibited Pgt development, but thatthe effect was more pronounced in W6979. These results prompted the selection of timepoints earlier than 5 dpi for RNA-sequencing (RNA-seq) analysis. A time based comparisonof differentially expressed (DE) transcripts showed two phases of the APR response at 1 and3 dpi. The majority of differentially expressed transcripts in W1406 were induced at 3 dpi butin W6979 at 1 dpi. The current hypothesis maintains that the activation of an earlier defenceresponse in W6979 caused a notable decrease of Pgt development in this line. The defenceresponse in W1406 was delayed but still significantly decreased Pgt development. RNA-seqalso identified several transcripts encoding putative effectors in Pgt. A comparison ofdifferentially expressed between the APR lines and 37-07 identified a number of candidateAPR associated transcripts. The current study therefore delivered a multifaceted descriptionof the APR response in W1406 and W6979 and its effect on Pgt development.

[发布机构] University of the Free State