WHY2 (At1g71260, Q8VYF7) - manual literature synthesis

No deep-research API was available for this review; this synthesis was written by hand from the cached
publications in publications/ and the UniProt record. Quotes are verbatim from the cached files.

Identity and family

• WHIRLY2 (AtWHY2) is one of three Arabidopsis Whirly proteins, a small plant-specific family of
  single-stranded DNA (ssDNA) binding proteins with a Whirly fold (Pfam PF08536, InterPro IPR013742).
  The 238-aa precursor carries a predicted 29-residue mitochondrial transit peptide (UniProt FT TRANSIT 1..29).
• The Arabidopsis WHY2 Whirly domain (residues 45-212) was crystallised (PDB 4KOP) and forms a tetramer
  PMID:24192350.
  DNA-contacting residues defined in the potato StWHY2-ssDNA structures are conserved in AtWHY2
  PMID:24192350.

Localisation

• Mitochondrial targeting was shown by in vitro import and GFP fusions PMID:15967440 (abstract only in cache).
• Stable WHIRLY2:GFP lines co-localise with TMRM and show punctate intramitochondrial spots
  PMID:32490348.
• mtDNA immunoprecipitation shows AtWhy2 is bound along the whole mitochondrial genome
  PMID:18423020.
• WHY2 co-purifies with ODB1 (RAD52-1) in large nucleoprotein complexes in mitochondria PMID:22762281 (abstract only).
• Together these support a mitochondrial nucleoid location PMID:32490348.
  No experimental evidence places WHY2 in chloroplasts; the paralogue WHY3, not WHY2, was found dual-targeted (PMID:32490348).

Molecular function

• Recombinant AtWhirly2 binds ssDNA with nanomolar affinity and is tetrameric
  PMID:30698803.
• Mechanism (from the potato orthologue StWHY2): non-sequence-specific binding in which ssDNA is held between
  adjacent subunits and made unavailable for duplex formation PMID:20551348. Potato WHY2 tetramers further assemble into 24-mers on long ssDNA, dependent on the KGKAAL motif lysine (PMID:21911368; potato WHY2 and Arabidopsis WHY1 were tested, not AtWHY2).
• RNA: Whirly proteins, including WHY2, were captured in Arabidopsis mRNA interactome studies PMID:32344669; the physiological relevance for mitochondrial RNA is unknown.

Biological role

• Genome stability / DSB repair in mitochondria: after ciprofloxacin-induced organellar DSBs, why2-1 mutants
  accumulate microhomology-mediated mtDNA rearrangements PMID:20551348.
  The effect is organelle-specific (plastid genome unaffected in why2-1).
• In vitro, AtWhirly2 blocks microhomology-mediated end-joining by organellar DNA polymerases PolIA/PolIB,
  consistent with competition for the ssDNA of a resected break PMID:30698803.
• Overexpression lowers mtDNA content and mitochondrial transcripts; knockout has no visible phenotype under
  normal growth (PMID:18423020), but why2-1 mitochondria show disorganised nucleoids, fewer cristae and impaired
  seed germination (PMID:32490348). These are phenotypes and do not by themselves define new process terms.
• Defense response / nuclear transcription: these roles were described for potato StWHY1 and Arabidopsis AtWHY1
  PMID:15708347; there is no
  WHY2-specific evidence.