How wild poppies use two unrelated genetic systems to avoid inbreeding

A missing biological lock

Field poppies avoid fertilising themselves by recognising and rejecting their own pollen. Biologists thought they understood this plant self-incompatibility system through a well-known gene pair named PrpS and PrsS. However, looking across different poppy strains revealed a puzzle. In many poppy haplotypes, those familiar genes were completely absent.

An unexpected replacement

To find out what was going on, researchers examined the chromosomal region called the S locus. Instead of variations of the old genes, they discovered a completely different gene pair segregating at the exact same location: SOPT and SGRP.

These genes are idiomorphs. That means they occupy the same position on the chromosome in different plants, yet they share no evident common ancestry. The poppy system is not controlled by regular homologous gene variants that branched apart over time. Instead, it relies on two entirely distinct, multiallelic idiomorph pairs that somehow share the exact same role.

Testing the new pair

Finding the genes was not enough to confirm their job. The researchers used heterologous expression, inserting the poppy SOPT and SGRP genes into another plant, Arabidopsis thaliana. When expressed in this host, the new gene pair functioned successfully, blocking self-fertilisation just as the original pair does.

This shows that natural selection built two completely independent mechanisms to govern allorecognition in the very same species.

What we still do not know

The exact proportion of poppies that lack the original PrpS-PrsS pair remains uncounted beyond the observation that it is missing in many plants. Functional tests have so far been verified in Arabidopsis thaliana rather than by directly altering genes in wild poppies. Researchers also do not yet know the evolutionary timeline that placed these two unrelated gene systems into the same locus, nor the exact molecular signals they use to halt pollination.