Transcriptomic analyses reveal physiological changes in sweet orange roots affected by citrus blight

Area of Science:

• Plant Pathology
• Molecular Biology
• Genomics

Background:

• Citrus blight is a progressive decline disease affecting commercial citrus production.
• The exact cause of citrus blight is unknown, but transmission via root grafts suggests a viral origin.
• Diagnosis relies on identifying physical blockage of xylem vessels, hindering water transport.

Purpose of the Study:

• To investigate the molecular mechanisms underlying citrus blight by analyzing transcriptomic changes in affected trees.
• To identify specific genes and pathways involved in the disease progression and xylem dysfunction.

Main Methods:

• RNA sequencing (RNA-Seq) was performed on root tissues from seven symptomatic citrus trees and one healthy control.
• Transcriptomic data were analyzed to compare gene expression patterns between healthy and diseased trees.
• Quantitative real-time PCR (RT-qPCR) was used to validate the expression of specific transcripts, including citrus endogenous pararetrovirus.

Main Results:

• Citrus blight stress led to down-regulation of aquaporin and cellulose synthase genes, and up-regulation of lignin biosynthesis genes.
• Genes involved in carbohydrate metabolism, nucleotide synthesis, signaling, and hormone pathways were significantly down-regulated.
• Elevated transcripts of a pararetrovirus were detected in the roots of blighted trees.

Conclusions:

• Citrus blight involves complex transcriptomic alterations, including changes in primary and secondary metabolism, nuclear transport, and hormone pathways.
• The observed gene expression patterns suggest an irreversible decline in affected plants.
• Imbalances in wood formation pathways, potentially driven by altered cellulose synthase and lignin production, likely contribute to xylem blockage, a hallmark symptom of citrus blight.