PIT2 (UMAG_01375, A0A0D1EAR7) — curation notes

2026-10-02 initial review

Sources: UniProt entry, GOA (3 rows, all extracellular region), the Falcon deep research file, and the
cached papers PMID:21692877 (abstract only), PMID:27093436 (full text), PMID:23459172 (full text, newly
cached) and PMID:30952847 (full text, newly cached).

Identity

• Secreted 120-aa effector of Ustilago maydis. Signal peptide 1-25. Encoded next to pit1
  (transmembrane protein) in the pit cluster. Not related to the rice NLR also called Pit2.
• "Pit2 is secreted to the biotrophic interface" PMID:21692877

Molecular function: PLCP inhibitor

• PMID:23459172
• Y2H: binds CP1A, CP1B, CP2 and XCP2, but not CatB. Co-IP with CP2. Recombinant Pit2 at 10 uM inhibits
  CP2 by 85% PMID:23459172
• Specificity PMID:23459172
• PID14 motif (aa 44-57). Mutant 49-53 loses inhibition PMID:23459172. The mutant proteins still localize to the interface, so their loss of virulence is biochemical and not a trafficking defect.
• The free PID14 peptide also inhibits CatB, so the specificity of the intact protein comes from the
  flanking regions PMID:23459172.
• Substrate-mimic model PMID:30952847
• Both processing and inhibition are needed PMID:30952847.

Process / pathway

• The targets CP1 and CP2 process PROZIP1 into Zip1, which amplifies SA defence (Ziemann et al. 2018,
  via the deep research file; that paper is not cached here).
• Deletion phenotype PMID:23459172

Regulation (fungal side, not a Pit2 function)

• The UPR regulator Cib1 binds the UPRE in the pit1/pit2 promoter. ER stress increases secretion
  PMID:27093436.

Curation decisions

• All 3 extracellular region rows: ACCEPT.
• NEW GO:0004869 cysteine-type endopeptidase inhibitor activity (IDA, PMID:23459172). Comparator:
  P. infestans EPIC2B (D0NBV3), an apoplastic PLCP-inhibitor effector, has GO:0004869/GO:0030414 in GOA.
• NEW GO:0140403 effector-mediated suppression of host innate immune response (IMP). EPIC2B carries the
  parent term GO:0052170. I did not use GO:0140502 (SA-signalling suppression, which CMU1 uses) because
  Pit2 acts on proteases that amplify SA signalling, not on SA itself. This is raised as a question in the
  review.
• NEW GO:0140593 host apoplast, which matches CMU1.
• GO ids checked in QuickGO: GO:0004869, GO:0140403 (is_a GO:0052170, GO:0140590), GO:0140593 and
  GO:0140502 are all current.

Open / not used

• A 2025 bioRxiv preprint (Mendoza-Rojas et al.) reports a Pit2-derived peptide that activates the fungal
  GPCR Gpe1. It is not peer reviewed and was not annotated.