Co-infection of Sweet Orange with Severe and Mild Strains of Citrus tristeza virus Is Overwhelmingly Dominated by the Severe Strain on Both the Transcriptional and Biological Levels

Abstract

Citrus tristeza is one of the most destructive citrus diseases and is caused by the phloem-restricted Closterovirus, Citrus tristeza virus. Mild strain CTV-B2 does not cause obvious symptoms on indicators whereas severe strain CTV-B6 causes symptoms, including stem pitting, cupping, yellowing, and stiffening of leaves, and vein corking. Our laboratory has previously characterized changes in transcription in sweet orange separately infected with CTV-B2 and CTV-B6. In the present study, transcriptome analysis of Citrus sinensis in response to double infection by CTV-B2 and CTV-B6 was carried out. Four hundred and eleven transcripts were up-regulated and 356 transcripts were down-regulated prior to the onset of symptoms. Repressed genes were overwhelmingly associated with photosynthesis, and carbon and nucleic acid metabolism. Expression of genes related to the glycolytic, oxidative pentose phosphate (OPP), tricarboxylic acid cycle (TCA) pathways, tetrapyrrole synthesis, redox homeostasis, nucleotide metabolism, protein synthesis and post translational protein modification and folding, and cell organization were all reduced. Ribosomal composition was also greatly altered in response to infection by CTV-B2/CTV-B6. Genes that were induced were related to cell wall structure, secondary and hormone metabolism, responses to biotic stress, regulation of transcription, signaling, and secondary metabolism. Transport systems dedicated to metal ions were especially disturbed and ZIPs (Zinc Transporter Precursors) showed different expression patterns in response to co-infection by CTV-B2/CTV-B6 and single infection by CTV-B2. Host plants experienced root decline that may have contributed to Zn, Fe, and other nutrient deficiencies. Though defense responses, such as, strengthening of the cell wall, alteration of hormone metabolism, secondary metabolites, and signaling pathways, were activated, these defense responses did not suppress the spread of the pathogens and the development of symptoms. The mild strain CTV-B2 did not provide a useful level of cross-protection to citrus against the severe strain CTV-B6.

In silico analysis of the grapefruit sRNAome, transcriptome and gene regulation in response to CTV-CDVd co-infection

“…Many diverse “genes” were found differentially regulated in response CTV-CDVd co-infection across both grapefruit varieties. Similar to the results of previous studies on the infection of either CTV [ 53 – 57 ] or CDVd [ 58 ] in different citrus species and in P. trifoliata , grapefruit metabolic, disease response, structural and phytohormone-related pathways seem to be affected by the co-infection. Genes with known involvement in plant disease responses were mostly grouped into leucine-rich repeat (which include tobacco mosaic virus resistance protein N-like) and ankyrin repeat-containing protein coding genes.…”

“…Genes with known involvement in plant disease responses were mostly grouped into leucine-rich repeat (which include tobacco mosaic virus resistance protein N-like) and ankyrin repeat-containing protein coding genes. The number of chloroplast-associated genes with altered expression supports the hypothesis that the CTV-CDVd co-infection influences the photosynthetic pathways of grapefruit, which was previously shown for CTV infection in sweet orange [ 56 , 57 ] and Mexican lime [ 54 , 59 ].…”

Zinc and Copper Ions Differentially Regulate Prion-Like Phase Separation Dynamics of Pan-Virus Nucleocapsid Biomolecular Condensates

“…Modulated SOD-1 expression and activity has also been observed from infection by respiratory syncytial virus and influenza A virus [ 269 , 270 ]. Cu/Zn-SOD activity is also modulated in plants infected by viruses [ 271 ].…”

Pochonia chlamydosporia Induces Plant-Dependent Systemic Resistance to Meloidogyne incognita

“…Other local plant defense mechanisms induced by P. chlamydosporia against RKN have been reported, including the increase of the peroxidases ( POX ) and poliphenoloxidases ( PPO ) enzymes activity at root nematode invasion stage (24–96 h after nematode inoculation) (de Medeiros et al, 2015). However, considering that P. chlamydosporia does not extensively colonize the root (Maciá-Vicente et al, 2009; Escudero and Lopez-Llorca, 2012), even being improved by chitosan irrigation (Escudero et al, 2017), the effect of local defense mechanisms alone may be insufficient to achieve significant nematode suppression.…”

“…Three 10-seed subsamples per Erlenmeyer were plated onto CMA and incubated at 25 ± 2°C in the dark for 2 weeks to assess putative contaminations prior to being used. The viability of the chlamydospores was assessed as in Escudero et al (2017).…”