Transcriptome Profiling of Huanglongbing (HLB) Tolerant and Susceptible Citrus Plants Reveals the Role of Basal Resistance in HLB Tolerance

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.

Can CRISPR Win the Battle against Huanglongbing?

“…Recently, RNA-Seq was conducted using two genetically close related cultivars HLB tolerant "Jackson" grapefruit hybrid and HLB susceptible "Marsh" grapefruit. The results showed that basal defense played an important role in resistance to HLB [32]. Because small RNAs participate in disease resistance [33], small RNA profiling was determined in HLB infected sweet orange.…”

Efecto del HLB sobre el rendimiento de limón mexicano en Colima, México

“…Los síntomas de esta enfermedad están asociados a la presencia de una α-proteobacteria 'Candidatus Liberibacter asiáticus' del tipo Gram-negativa, restringida al floema de las plantas hospederas y que es diseminada por el psílido asiático de los cítricos (Diaphorina citri). Actualmente se le considera como la enfermedad más destructiva de los cítricos (Wang et al, 2016) y se ha convertido en la más seria amenaza para la producción de cítricos en todo el mundo (McCollum et al, 2016). No se conoce cura para los árboles infectados (Gottwald et al, 2007), los que en poco tiempo se vuelven decadentes e improductivos, y en algunos casos mueren.…”

“…The symptoms of this disease are associated with the presence of an α-proteobacteria 'Candidatus Liberibacter asiaticus' of Gram-negative type, restricted to phloem of host plants and spreaded by the Asian citrus psyllid (Diaphorina citri). It is now considered as the most destructive citrus disease (Wang et al, 2016) and has become the most serious threat to citrus production worldwide (McCollum et al, 2016). No cure for infected trees is known (Gottwald et al, 2007), which soon become decadent and unproductive, and in some cases die.…”

“…Moreover, studies at the genomic level have been ascertained that HLB can alter the expression of a large number of genes in various organs of infected plants (Kim et al, 2009;Liao and Burns, 2012;Mafra et al, 2013;Zheng and Zhao, 2013;Aritua et al, 2013;Zhong et al, 2015;Wang et al, 2016). Some genes are overexpressed, but others reduce its expression.…”

“…Some genes are overexpressed, but others reduce its expression. Genes whose expression is altered are mainly related to the plant's defense systems (Kim et al, 2009;Rawat et al, 2015;Wang et al, 2016), the sucrose and starch metabolism (Xu et al, 2015;Rawat et al, 2015;Wang et al, 2016), synthesis and signaling hormones (Martinelli et al, 2012), nutrients absorption and transport (Zhang et al, 2015;Rawat et al, 2015;Zhong et al, 2015). Mafra et al, 2013;Zheng y Zhao, 2013;Aritua et al, 2013;Zhong et al, 2015;Wang, et al, 2016).…”