Abstract
Huanglongbing (HLB) is currently the most destructive disease of citrus worldwide. Although there is no immune cultivar, field tolerance to HLB within citrus and citrus relatives has been observed at the USDA Picos farm at Ft. Pierce, Florida, where plants have been exposed to a very high level of HLB pressure since 2006. In this study, we used RNA-Seq to evaluate expression differences between two closely related cultivars after HLB infection: HLB-tolerant “Jackson” grapefruit-like-hybrid trees and HLB susceptible “Marsh” grapefruit trees. A total of 686 genes were differentially expressed (DE) between the two cultivars. Among them, 247 genes were up-expressed and 439 were down-expressed in tolerant citrus trees. We also identified a total of 619 genes with significant differential expression of alternative splicing isoforms between HLB tolerant and HLB susceptible citrus trees. We analyzed the functional categories of DE genes using two methods, and revealed that multiple pathways have been suppressed or activated in the HLB tolerant citrus trees, which lead to the activation of the basal resistance or immunity of citrus plants. We have experimentally verified the expressions of 14 up-expressed genes and 19 down-expressed genes on HLB-tolerant “Jackson” trees and HLB-susceptible “Marsh” trees using real time PCR. The results showed that the expression of most genes were in agreement with the RNA-Seq results. This study provided new insights into HLB-tolerance and useful guidance for breeding HLB-tolerant citrus in the future.
Highlights
Huanglongbing (HLB), commonly known as citrus “greening”, is the most economically destructive disease of citrus worldwide
We extended our study to whose average expressions with log2 based fold ratios >1 and
The results showed that the gene expressions of most genes in agreement with the RNA-Seq results had similar expression pattern after HLB infection, which further supported the tolerant citrus and the susceptible citrus may have different defense response to Liberibacter asiaticus” (Las) infection
Summary
Huanglongbing (HLB), commonly known as citrus “greening”, is the most economically destructive disease of citrus worldwide. There is no immune cultivar, some resistance or field tolerance to HLB within citrus and citrus relatives has been described (Miyakawa, 1980; Nariani, 1981; Miyakawa and Yuan, 1990; Halbert and Manjunath, 2004; Sharma et al, 2004). Compared to other tested cultivars within individual experiments, lower susceptibility to HLB associated with Las, has been reported for limes (Schwarz et al, 1973; Shokrollah et al, 2009), pummelos (Schwarz et al, 1973; Koizumi et al, 1997), lemons (Schwarz et al, 1973; Nariani, 1981; Cheema et al, 1982), some mandarin types (e.g., “Ladu” and “Som Pan” in Thailand, Koizumi et al, 1997) and various non-cultivated Citrus or related species
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