There are so called PIN proteins, or PIN-formed proteins, in plants. What does this acronym mean?

Wikipedia briefly explains the function of the protein but not the origin of the name. It's not explained even in the link-linked review paper, if I'm not missing something.


2 Answers 2


Like many genes and gene products, PIN proteins were named for a mutant phenotype and PIN is not actually an acronym; the source in your link does actually explain this (emphasis mine):

The significance and function of AtPIN1 was discovered through the phenotype generated by the loss-of-function mutation in the gene: mutant plants fail to develop floral organs properly and generate naked, pin-like inflorescences, which gave the name PIN-FORMED (PIN) to the family

Křeček, P., Skůpa, P., Libus, J., Naramoto, S., Tejos, R., Friml, J., & Zažímalová, E. (2009). The PIN-FORMED (PIN) protein family of auxin transporters. Genome biology, 10(12), 249.

  • $\begingroup$ Thanks. So it is explained there… (I was lazy to read more than the summary, then I've did just /\<[Pp][a-z]+(\s|-)[Ii][a-z]+(\s|-)[Nn][a-z]+/ regexp search). $\endgroup$
    – mykhal
    Commented Nov 3, 2018 at 16:54
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    $\begingroup$ It begs the question: why was “PIN” all-caps at all? When something is all-caps, it makes people think it’s an acronym. I’m not a geneticist, or even a biologist, by training. So please enlighten me if there’s some rule in the field that justifies all-caps. $\endgroup$
    – Kal
    Commented Nov 4, 2018 at 8:02
  • $\begingroup$ Explaining what actually is a “pin-like inflorescence” would be very helpful. $\endgroup$
    – mykhal
    Commented Jan 15, 2019 at 8:26

It is not an acronym; it is an abbreviation of pinnulate (or pinnulated), which means having the pinnulae of a pinnate leaf properly developed.

Gene symbols written in all caps indicate the wild-type condition of the organism: If a gene is referred to as PIN1, it means its product (an auxin transporter) permits normal branching (or at lest does not contribute to malformations); when it is written in lower case, pin1, it indicates the gene has a variant associated with a mutant (non-pinnate) phenotype.

PIN1: nothing is broken

pin1: a single stalk without pinnulae (in the case of Arabidopsis)

If the mutant looks like a pin, it is a co-incidence (probably a mnemonic suggested by a English-speaking teacher). The original meaning derives from pinna, which refers to the normal appearance of leaves and flowers.

  • $\begingroup$ Welcome and thanks for your answer. Can you add sources to support your claims and allow folks to background read on your answer? $\endgroup$
    – AliceD
    Commented Feb 7, 2021 at 20:17
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    $\begingroup$ Hearsay. That's the explanation I heard from folks in my orbit. Here's one example: youtu.be/jFiqj9NKQfc?t=1452 Apparently, while functionally accurate, it is incorrect as a matter of origin. The discovereres of PIN genes named them pin-forming. ncbi.nlm.nih.gov/pmc/articles/PMC160035/pdf/030677.pdf They do write gene names in lower case, so that's not where the confusion originated. There are pictures in the paper illustrating the mutant phenotypes. $\endgroup$
    – user101414
    Commented Feb 8, 2021 at 22:04

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