WRKY Transcription Factors Associated With NPR1-Mediated Acquired Resistance in Barley Are Potential Resources to Improve Wheat Resistance to Puccinia triticina

Abstract

Systemic acquired resistance (SAR) in <i>Arabidopsis</i> is established beyond the initial pathogenic infection or is directly induced by treatment with salicylic acid or its functional analogs (SA/INA/BTH). NPR1 protein and WRKY transcription factors are considered the master regulators of SAR. Our previous study showed that <i>NPR1</i> homologs in wheat (<i>Triticum aestivum</i> L.) and barley (<i>Hordeum vulgare</i> L.) regulated the expression of genes encoding pathogenesis-related (PR) proteins during acquired resistance (AR) triggered by <i>Pseudomonas syringae</i> pv. <i>tomato</i> DC3000. In the present examination, AR induced by <i>P. syringae</i> DC3000 was also found to effectively improve wheat resistance to <i>Puccinia triticina</i> (<i>Pt</i>). However, with more complex genomes, genes associated with this SAR-like response in wheat and barley are largely unknown and no specific <i>WRKYs</i> has been reported to be involved in this biological process. In our subsequent analysis, barley transgenic line overexpressing wheat <i>wNPR1</i> (wNPR1-OE) showed enhanced resistance to <i>Magnaporthe oryzae</i> isolate Guy11, whereas AR to Guy11 was suppressed in a barley transgenic line with knocked-down barley <i>HvNPR1</i> (HvNPR1-Kd). We performed RNA-seq to reveal the genes that were differentially expressed among these transgenic lines and the wild-type barley plants during the AR. Several <i>PR</i> and BTH-induced (<i>BCI</i>) genes were designated as downstream genes of <i>NPR1</i>. The expression of few <i>WRKYs</i> was significantly associated with <i>NPR1</i> expression during the AR events. The transient expression of three <i>WRKY</i> genes, including <i>HvWRKY6</i>, <i>HvWRKY40</i>, and <i>HvWRKY70</i>, in wheat leaves by <i>Agrobacterium</i>-mediated infiltration enhanced the resistance to <i>Pt</i>. In conclusion, a profile of genes associated with <i>NPR1</i>-mediated AR in barley was drafted and <i>WRKYs</i> discovered in the current study showed a substantial potential for improving wheat resistance to <i>Pt</i>.