Mapping a leaf rust resistance gene LrOft in durum wheat Ofanto and its suppressor SuLrOft in common wheat.

Epidemics of leaf rust (caused by the fungal pathogen Puccinia triticina Erikss., Pt) raise concerns regarding sustainability of wheat production. Deployment of resistant cultivars is the most effective and economic strategy for combating this disease. Ofanto is a durum wheat cultivar that exhibits high resistance to Pt race PHT throughout its entire growing period. In the present study, we identified a leaf rust resistance gene in Ofanto and temporarily designated it as LrOft. LrOft was mapped to a 2.5 cM genetic interval in chromosome arm 6BL between Indel markers 6B6941 and 6B50L24. During introgression of LrOft from Ofanto to common wheat it was observed that F1 plants of Ofanto crossed with Shi4185 exhibited leaf rust resistance whereas the F1 of Ofanto crossed with ND4503 was susceptible. In order to map the presumed suppressor locus, a Shi4185/ND4503//Ofanto three-way pentaploid population was generated and SuLrOft was mapped on chromosome arm 2AS. SuLrOft was mapped within a 2.6 cM genetic interval flanked by 2AS50L14 and 2AS50L6. Fine mapping using 2,268 plants of the three-way cross narrowed the suppressor locus to a 68.2-kbp physical interval according to IWGSC RefSeq v1.1. Sequence analysis of genes in the physical interval revealed that TraesCS2A02G110800 encoding an RPP-13-like protein with an NB-ARC domain was a potential candidate for SuLrOft.

Exogenous sodium diethyldithiocarbamate, a Jasmonic acid biosynthesis inhibitor, induced resistance to powdery mildew in wheat.

Jasmonic acid (JA) is an important plant hormone associated with plant-pathogen defense. To study the role of JA in plant-fungal interactions, we applied a JA biosynthesis inhibitor, sodium diethyldithiocarbamate (DIECA), on wheat leaves. Our results showed that application of 10 mM DIECA 0-2 days before inoculation effectively induced resistance to powdery mildew (Bgt) in wheat. Transcriptome analysis identified 364 up-regulated and 68 down-regulated differentially expressed genes (DEGs) in DIECA-treated leaves compared with water-treated leaves. Gene ontology (GO) enrichment analysis of the DEGs revealed important GO terms and pathways, in particular, response to growth hormones, activity of glutathione metabolism (e.g., glutathione transferase activity), oxalate oxidase, and chitinase activity. Gene annotaion revealed that some pathogenesis-related (PR) genes, such as PR1.1, PR1, PR10, PR4a, Chitinase 8, beta-1,3-glucanase, RPM1, RGA2, and HSP70, were induced by DIECA treatment. DIECA reduced JA and auxin (IAA) levels, while increased brassinosteroid, glutathione, and ROS lesions in wheat leaves, which corroborated with the transcriptional changes. Our results suggest that DIECA can be applied to increase plant immunity and reduce the severity of Bgt disease in wheat fields.

Glycerol-Induced Powdery Mildew Resistance in Wheat by Regulating Plant Fatty Acid Metabolism, Plant Hormones Cross-Talk, and Pathogenesis-Related Genes.

Our previous study indicated that glycerol application induced resistance to powdery mildew (Bgt) in wheat by regulating two important signal molecules, glycerol-3-phosphate (G3P) and oleic acid (OA18:1). Transcriptome analysis of wheat leaves treated by glycerol and inoculated with Bgt was performed to identify the activated immune response pathways. We identified a set of differentially expressed transcripts (e.g., TaGLI1, TaACT1, and TaSSI2) involved in glycerol and fatty acid metabolism that were upregulated in response to Bgt infection and might contribute to G3P and OA18:1 accumulation. Gene Ontology (GO) enrichment analysis revealed GO terms induced by glycerol, such as response to jasmonic acid (JA), defense response to bacterium, lipid oxidation, and growth. In addition, glycerol application induced genes (e.g., LOX, AOS, and OPRs) involved in the metabolism pathway of linolenic and alpha-linolenic acid, which are precursor molecules of JA biosynthesis. Glycerol induced JA and salicylic acid (SA) levels, while glycerol reduced the auxin (IAA) level in wheat. Glycerol treatment also induced pathogenesis related (PR) genes, including PR-1, PR-3, PR-10, callose synthase, PRMS, RPM1, peroxidase, HSP70, HSP90, etc. These results indicate that glycerol treatment regulates fatty acid metabolism and hormones cross-talk and induces the expression of PR genes that together contribute to Bgt resistance in wheat.