Transcriptional profiling of rice early response to Magnaporthe oryzae identified OsWRKYs as important regulators in rice blast resistance

Abstract

Rice blast disease is a major threat to rice production worldwide, but the mechanisms underlying rice resistance to the causal agent Magnaporthe oryzae remain elusive. Therefore, we carried out a transcriptome study on rice early defense response to M. oryzae. We found that the transcriptional profiles of rice compatible and incompatible interactions with M. oryzae were mostly similar, with genes regulated more prominently in the incompatible interactions. The functional analysis showed that the genes involved in signaling and secondary metabolism were extensively up-regulated. In particular, WRKY transcription factor genes were significantly enriched among the up-regulated genes. Overexpressing one of these WRKY genes, OsWRKY47, in transgenic rice plants conferred enhanced resistance against rice blast fungus. Our results revealed the sophisticated transcriptional reprogramming of signaling and metabolic pathways during rice early response to M. oryzae and demonstrated the critical roles of WRKY transcription factors in rice blast resistance.

Figure 1. The disease symptoms on IRBL18, IRBL22 and LTH leaves at 7 days post-inoculation.

The inoculation experiment was repeated three times (n = 10 seedlings) with similar results.

Figure 2. Differentially expressed genes (DEGs) identified from the transcriptome study.

A: The venn diagram of DEGs in IRBL18, IRBL22 and LTH. The numbers of up- and down-regulated genes were shown in red and green, respectively. B: Hierarchical clustering of the log2-transformed fold changes. The scale bar displays log2-transformed fold changes. C: Scatter plot of log2-transformed fold changes.

Figure 3. Overview of the transcriptional changes in IRBL18 at 24 hours post-inoculation.

Genes significantly up- (red) or down-regulated (green) in fungal-inoculated leaf samples relative to mock-inoculated are illustrated. The scale bar displays log2-transformed fold changes.

Figure 4. The expression patterns of receptor kinase and nucleotide binding and leucine rich repeat (NB-LRR) genes.

A: The expression patterns of NB-LRR genes. B: The expression patterns of receptor kinase genes, with the family names shown on the right side. The scale bar displays log2-transformed fold changes.

Figure 5. Transcriptional changes in shikimate and phenylpropanoid biosynthesis pathways.

A: The expression patterns of genes in the shikimate and phenylpropanoid biosynthesis pathway. The scale bar displays log2-transformed fold changes. B: The metabolic view of shikimate and phenylpropanoid biosynthesis pathways. The steps catalyzed by enzymes encoded by up-regulated genes were shown in red. The shikimate and phenylalanine biosynthesis pathways were highlighted with pink background and the phenylpropanoid biosynthesis pathway was highlighted with light blue background. Gene abbreviations were listed in Table S5.

Figure 6. The sliding window analysis of genes involved in signaling (A) and secondary metabolism (B).

The solid lines represent the percentages of certain functional category in a 500-gene window in IRBL18 (red), IRBL22 (blue) and LTH (green). The blue dotted lines represent the 95% confidence levels.

Figure 7. The expression patterns of OsWRKYs (A) and the trans-activation activities of selected OsWRKYs (B).

The scale bar in (A) displays log2-transformed fold changes.

Figure 8. Overexpression of OsWRKY47 enhanced rice resistance to Magnaporthe oryzae strain 96-4-1a.

A: The disease symptoms on TP309, pUbi:OsWRKY47#16 and #7 transgenic plants at 7 days post-inoculation. The inoculation experiments were repeated three time (n = 15 seedlings) with similar results. B, C: The expression levels of OsWRKY47 and PR10 in TP309 and pUbi:OsWRKY47 transgenic plants determined by quantitative RT-PCR. The expression levels were standardized to OsUBQ and the value in TP309 was set at 1.0. Error bars in (B) and (C) represent the SD from three biological replicates, each containing at least 10 seedlings. The expression levels that differ significantly (P<0.05) from those in TP309 were marked with asterisks.