Genome-wide characterization of heavy metal-associated isoprenylated plant protein gene family from Citrus sinensis in response to huanglongbing.

Introduction: Heavy metal-associated isoprenylated plant proteins (HIPPs) play vital roles in maintaining heavy metal balance and responding to both biotic and abiotic stresses in vascular plants. However, the role of HIPPs in the response to Huanglongbing (HLB), a harmful disease of citrus caused by the phloem-colonizing bacterium Candidatus Liberibacter asiaticus (CLas), has not been examined. Methods and results: In this study, a total of 26 HIPP genes were identified in Citrus sinensis, and they were grouped into 5 clades. The CsHIPP genes are distributed on 8 chromosomes and exhibited considerable synteny with HIPPs found in Arabidopsis thaliana. Additionally, we analyzed the gene structure, conserved motifs and domains of the CsHIPPs. Various cis-acting elements related to plant hormones and stress responses were identified in the promoters of CsHIPPs. Public transcriptome data and RT-qPCR analysis showed that the expression level of CsHIPP03 was significantly reduced in samples infected by CLas and Xanthomonas citri ssp. citri (Xcc). Furthermore, silencing the homologous gene of CsHIPP03 in Nicotiana benthamiana increased the disease resistance of plants to bacteria. Discussion: Our results provide a basis for functional studies of HIPP gene family in C. sinensis, highlighting their functions in bacterial resistance, and improve our understanding to the susceptibility mechanism of HLB.

Transcriptome analysis of Citrus sinensis reveals potential responsive events triggered by Candidatus Liberibacter asiaticus.

Citrus Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), is a devastating immune-mediated disorder that has a detrimental effect on the citrus industry, with the distinguishing feature being an eruption of reactive oxygen species (ROS). This study explored the alterations in antioxidant enzyme activity, transcriptome, and RNA editing events of organelles in C. sinensis during CLas infection. Results indicated that there were fluctuations in the performance of antioxidant enzymes, such as ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), peroxidase (POD), and superoxide dismutase (SOD), in plants affected by HLB. Transcriptome analysis revealed 3604 genes with altered expression patterns between CLas-infected and healthy samples, including those associated with photosynthesis, biotic interactions, and phytohormones. Samples infected with CLas showed a decrease in the expression of most genes associated with photosynthesis and gibberellin metabolism. It was discovered that RNA editing frequency and the expression level of various genes in the chloroplast and mitochondrion genomes were affected by CLas infection. Our findings provide insights into the inhibition of photosynthesis, gibberellin metabolism, and antioxidant enzymes during CLas infection in C. sinensis.

Systematic analysis of the thioredoxin gene family in Citrus sinensis: identification, phylogenetic analysis, and gene expression patterns.

Thioredoxin (TRX) proteins play essential roles in reactive oxygen species scavenging in plants. We executed an exhaustive analysis of the TRX gene family in Citrus sinensis (CsTRXs), encompassing identification, phylogenetic analysis, detection of conserved motifs and domains, gene structure, cis-acting elements, gene expression trends, and subcellular localization analysis. Our findings established that a total of 22 CsTRXs with thioredoxin domains were identified in the genome of C. sinensis. Phylogenetic analysis indicated that CsTRXs were divided into six subclusters. Conserved motifs analysis of CsTRXs indicated a wide range of conserved motifs. A significant number of cis-acting elements associated with both abiotic and biotic stress responses, inclusive of numerous phytohormone-related elements, were detected in the promoter regions of CsTRXs. The expression levels of CsTRXs including CsTRXf1, CsTRXh1, CsTRXm1, CsTRXo3, CsTRXx2 and CsTRXy1 were observed to be reduced upon pathogen infection. Subcellular localization analysis found that CsTRXf1, CsTRXm1, CsTRXo3, CsTRXx2 and CsTRXy1 were predominantly localized in chloroplasts, whereas CsTRXh1 was distributed indiscriminately. This research yields integral data on CsTRXs, facilitating future efforts to decipher the gene functions of CsTRXs.