Genome resequencing and transcriptome profiling reveal structural diversity and expression patterns of constitutive disease resistance genes in Huanglongbing-tolerant Poncirus trifoliata and its hybrids. (15th November 2017)

• Record Type: Journal Article
• Authors: Rawat, Nidhi; Kumar, Brajendra; Albrecht, Ute; Du, Dongliang; Huang, Ming; Yu, Qibin; Zhang, Yi; Duan, Yong-Ping; Bowman, Kim D; Gmitter, Fred G; Deng, Zhanao
• Is Part Of: Horticulture research. Volume 4(2017)
• Publication Date: 2017-11-15
• Subjects: Agricultural genetics -- Plant genetics; Horticulture -- Research -- Periodicals; 635.072
• DOI: 10.1038/hortres.2017.64
• Languages: English
• ISSNs: 2052-7276

Abstract

Abstract: Huanglongbing (HLB) is the most destructive bacterial disease of citrus worldwide. While most citrus varieties are susceptible to HLB, Poncirus trifoliata, a close relative of Citrus, and some of its hybrids with Citrus are tolerant to HLB. No specific HLB tolerance genes have been identified in P. trifoliata but recent studies have shown that constitutive disease resistance (CDR) genes were expressed at much higher levels in HLB-tolerant Poncirus hybrids and the expression of CDR genes was modulated by Candidatus Liberibacter asiaticus ( C Las), the pathogen of HLB. The current study was undertaken to mine and characterize the CDR gene family in Citrus and Poncirus and to understand its association with HLB tolerance in Poncirus . We identified 17 CDR genes in two citrus genomes, deduced their structures, and investigated their phylogenetic relationships. We revealed that the expansion of the CDR family in Citrus seems to be due to segmental and tandem duplication events. Through genome resequencing and transcriptome sequencing, we identified eight CDR genes in the Poncirus genome ( PtCDR1 - PtCDR8 ). The number of SNPs was the highest in PtCDR2 and the lowest in PtCDR7 . Most of the deletion and insertion events were observed in the UTR regions of Citrus and Poncirus CDR genes. PtCDR2 and PtCDR8 were in abundance in the leaf transcriptomes of two HLB-tolerant Poncirus genotypes and were also upregulated in HLB-tolerant, Poncirus hybrids as revealed by real-time PCR analysis. These two CDR genes seem to be good candidate genes for future studies of their role in citrus- C Las interactions. Abstract : Citrus diseases: Candidate genes against citrus greening A resistance gene family in both Citrus plants and the related Poncirus provides genes that may protect against a devastating disease. Citrus greening disease, also known as 'huanglongbing, ' is the most destructive bacterial disease of citrus crops worldwide. Most Citrus varieties, such as oranges, grapefruits, and lemons, are susceptible to huanglongbing, but the closely related trifoliate orange ( Poncirus ), often used as a hardy rootstock for Citrus, is tolerant. An international team led by Zhanao Deng at the University of Florida, Wimauma, USA, used genetic and genomic techniques to characterize a family of 'constitutive disease resistance' ( CDR ) genes in Citrus and Poncirus . They found multiple CDR genes, and identified two in Poncirus which were abundant in resistant individuals and increased in activity when exposed to huanglongbing. These make good candidates for future breeding of huanglongbing-resistant citrus varieties.