Peng H, Chen Z, Fang Z, Zhou J, Xia Z, Gao L, Chen L, Li L, Li T, Zhai W, Zhang W.

Scientific Reports. 2015 Jul 17;5:12165. doi: 10.1038/srep12165.

http://www.nature.com/srep/2015/150717/srep12165/full/srep12165.html

Abstract

Rice bacterial blight (BB) is a devastating rice disease. The Xa21 gene confers a broad and persistent resistance against BB. We introduced Xa21 into Oryza sativa L ssp indica (rice 9311), through multi-generation backcrossing, and generated a nearly isogenic, blight-resistant 9311/Xa21 rice. Using next-generation sequencing, we profiled the transcriptomes of both varieties before and within four days after infection of bacterium Xanthomonas oryzae pv. oryzae. The identified differentially expressed (DE) genes and signaling pathways revealed insights into the functions of Xa21. Surprisingly, before infection 1,889 genes on 135 of the 316 signaling pathways were DE between the 9311/Xa21 and 9311 plants. These Xa21-mediated basal pathways included mainly those related to the basic material and energy metabolisms and many related to phytohormones such as cytokinin, suggesting that Xa21 triggered redistribution of energy, phytohormones and resources among essential cellular activities before invasion. Counter-intuitively, after infection, the DE genes between the two plants were only one third of that before the infection; other than a few stress-related pathways, the affected pathways after infection constituted a small subset of the Xa21-mediated basal pathways. These results suggested that Xa21 primed critically important genes and signaling pathways, enhancing its resistance against bacterial infection.

Figure 1: (A) Comparison of in-field phenotypes of the R and S lines after inoculation of the P6 strain of Xoo. (B) PCR validation of Xa21 being introduced into the genome of the R (9311/Xa21) plants using the molecular marker U1/I2 that was co-segregated with Xa21. (C) The AFLP result of the R and S plants using 24 pairs of AFLP primers. (D) Genotypic variations across chromosome 11 of the R rice line. (E) The expression of Xa21 in the R plants at various time points before and within the first four days after Xoo inoculation. (F) Comparison of the amount of bacteria, measured by the number of bacterial colonies, in the R and S plants in the first 10 days post inoculation of Xoo.