Unraveling Mitochondrial Genome Evolution in Puccinia striiformis f. sp. elymi, the Elymus Stripe Rust Fungus

Area of Science:

• Plant Pathology
• Mitochondrial Genomics
• Evolutionary Biology

Background:

• Mitochondrial evolution in host-specialized rust fungi, particularly Puccinia striiformis f. sp. elymi (Pse), is not well understood.
• Pse infects Elymus dahuricus and represents a specialized lineage within Puccinia striiformis.

Purpose of the Study:

• To assemble and characterize the complete mitochondrial genome of Pse.
• To investigate the evolutionary patterns and mechanisms driving mitochondrial genome size variation in Pse.
• To establish a genomic basis for studying reductive evolution in specialized rust lineages.

Main Methods:

• Assembly of the Pse mitogenome using PacBio HiFi sequencing.
• Comparative genomic analysis with P. striiformis f. sp. tritici (Pst).
• Phylogenomic analysis to determine evolutionary relationships.
• Identification and analysis of single nucleotide polymorphism (SNP) clusters.

Main Results:

• A complete circular mitogenome of 72,952 bp was assembled for Pse.
• The Pse mitogenome exhibits a 28.34% contraction compared to Pst, primarily driven by massive loss of mitochondrial introns.
• The mitogenome retains conserved protein-coding genes, tRNAs, and rRNAs, with negative GC-skew.
• Phylogenomic analysis strongly supports Pse as sister to the Pst clade.
• A SNP cluster in nad4 was identified as a potential marker for lineage differentiation.

Conclusions:

• Mitochondrial intron loss is a key driver of reductive evolution and genome size variation in host-specialized rust fungi like Pse.
• The characterized Pse mitogenome provides a foundation for future research into rust mitochondrial evolution.
• The identified SNP marker warrants further population-level validation for diagnostic applications.