Xu, Meirong


Publications (9)

Physiological variables influenced by “<i>Candidatus</i> Liberibacter asiaticus” infection in two citrus species

Citation
Wu et al. (2022). Plant Disease
Names
Ca. Liberibacter asiaticus
Subjects
Agronomy and Crop Science Plant Science
Abstract
“Candidatus Liberibacter asiaticus” (CLas) is the bacterium associated with the citrus disease known as Huanglongbing (HLB). This study evaluated the influence of CLas infection on a number of key plant physiological variables concerning photosynthesis, cell integrity, reactive oxygen species scavengers’ activity, and osmoregulation of two different species of citrus (the pomelo Citrus maxima (Burm.) Merr. and the mandarin C. reticulata cv. Tankan), relative to their measured CLas infection load. Results indicated all measured physiological variables excepting soluble sugar were affected by increased CLas infection titers, wherein the variety C. maxima proved overall more resistant than C. reticulata. CLas infection was linked in both plants to decrease in chlorophyll concentration, cell membrane permeability and malondialdehyde, as well as increased free proline and starch contents. Chlorophyll fluorescence measurements taken 9 months after grafting the mandarin C. reticulata with CLas scions revealed a significant decrease in the photosynthesis variables Fv/Fm, Y(II) and QL, whilst NPQ increased significantly; C. maxima plants, on the other hand, did not show significant differences until the 12th month from infection exposure. The variables SOD, CAT, POD, and soluble protein initially increased and later decreased. In addition, progression of CLas replication in both citrus species was accompanied by rapid changes in three reactive oxygen species scavenging enzymes in C. maxima, while the pattern was different in C. reticulata. We hypothesize the observed interspecific differences in physiological change are related to their relative resistance against CLas infection. These results provide a scaffold for better describing the pathogenesis, selecting the most resistant breeds, or even validating pertaining omics research: ultimately these detailed observations can facilitate the diagnosis of CLas infection.

A Novel Microviridae Phage (CLasMV1) From “Candidatus Liberibacter asiaticus”

Citation
Zhang et al. (2021). Frontiers in Microbiology 12
Names
Ca. Liberibacter asiaticus
Subjects
Microbiology Microbiology (medical)
Abstract
“Candidatus Liberibacter asiaticus” (CLas) is an unculturable phloem-limited α-proteobacterium associated with citrus Huanglongbing (HLB; yellow shoot disease). HLB is currently threatening citrus production worldwide. Understanding the CLas biology is critical for HLB management. In this study, a novel single-stranded DNA (ssDNA) phage, CLasMV1, was identified in a CLas strain GDHZ11 from Guangdong Province of China through a metagenomic analysis. The CLasMV1 phage had a circular genome of 8,869 bp with eight open reading frames (ORFs). While six ORFs remain uncharacterized, ORF6 encoded a replication initiation protein (RIP), and ORF8 encoded a major capsid protein (MCP). Based on BLASTp search against GenBank database, amino acid sequences of both MCP and RIP shared similarities (coverage &amp;gt; 50% and identity &amp;gt; 25%) to those of phages in Microviridae, an ssDNA phage family. Phylogenetic analysis revealed that CLasMV1 MCP and RIP sequences were clustered with genes from CLas and “Ca. L. solanacearum” (CLso) genomes and formed a unique phylogenetic lineage, designated as a new subfamily Libervirinae, distinct to other members in Microviridae family. No complete integration form but partial sequence (∼1.9 kb) of CLasMV1 was found in the chromosome of strain GDHZ11. Read-mapping analyses on additional 15 HiSeq data sets of CLas strains showed that eight strains harbored complete CLasMV1 sequence with variations in single-nucleotide polymorphisms (SNPs) and small sequence insertions/deletions (In/Dels). PCR tests using CLasMV1-specific primer sets detected CLasMV1 in 577 out of 1,006 CLas strains (57%) from southern China. This is the first report of Microviridae phage associated with CLas, which expands our understanding of phage diversity in CLas and facilitates current research in HLB.

A Significantly High Abundance of “Candidatus Liberibacter asiaticus” in Citrus Fruit Pith: in planta Transcriptome and Anatomical Analyses

Citation
Fang et al. (2021). Frontiers in Microbiology 12
Names
Ca. Liberibacter asiaticus
Subjects
Microbiology Microbiology (medical)
Abstract
Huanglongbing, a highly destructive disease of citrus, is associated with the non-culturable phloem-limited α-proteobacterium “Candidatus Liberibacter asiaticus” (CLas). The distribution patterns of CLas in infected plant are variable and not consistent, which make the CLas detection and characterization more challenging. Here, we performed a systemic analysis of CLas distribution in citrus branches and fruits of 14 cultivars. A significantly high concentration of CLas was detected in fruit pith (dorsal vascular bundle) of 14 citrus cultivars collected at fruit maturity season. A 2-year monitoring assay of CLas population in citrus branches of “Shatangju” mandarin (Citrus reticulata Blanco “Shatangju”) revealed that CLas population already exhibited a high level even before the appearance of visual symptoms in the fruit rind. Quantitative analyses of CLas in serial 1.5-cm segments of fruit piths showed the CLas was unevenly distributed within fruit pith and tended to colonize in the middle or distal (stylar end) regions of pith. The use of CLas-abundant fruit pith for dual RNA-seq generated higher-resolution CLas transcriptome data compared with the leaf samples. CLas genes involved in transport system, flagellar assembly, lipopolysaccharide biosynthesis, virulence, stress response, and cell surface structure, as well as host genes involved in biosynthesis of antimicrobial-associated secondary metabolites, was up-regulated in leaf midribs compared with fruit pith. In addition, CLas infection caused the severe collapse in phloem and callose deposition in the plasmodesmata of fruit pith. The ability of fruit pith to support multiplication of CLas to high levels makes it an ideal host tissue for morphological studies and in planta transcriptome analyses of CLas–host interactions.

Draft Whole-Genome Sequence of a “ Candidatus Liberibacter asiaticus” Strain from Yunnan, China

Citation
Chen et al. (2019). Microbiology Resource Announcements 8 (3)
Names
Ca. Liberibacter asiaticus
Subjects
Genetics Immunology and Microbiology (miscellaneous) Molecular Biology
Abstract
The draft genome sequence of “ Candidatus Liberibacter asiaticus” strain YNJS7C, isolated from a navel orange tree in Yunnan Province, China, is presented here. The YNJS7C strain has a genome size of 1,258,986 bp, with a G+C content of 36.6%, 1,174 predicted open reading frames, and 53 RNA genes.