Two Stabiliser loci suppress Tam3 transposition without compromising transposase production in Antirrhinum

Snapdragon (Antirrhinum majus) exhibits occasional genetic instabilities that manifest as variegations and morphological chimeras. Stabiliser (St) is a historical locus that stabilizes phenotypically unstable or mutable traits in Antirrhinum. Here, we characterized two St loci, the previously described Old Stabiliser (OSt) and New Stabiliser (NSt), that specifically suppress the transposition of the Class II DNA transposable element Tam3 in Antirrhinum. Both St loci harbor Tam3 derivatives with unique structures: OSt contains a pseudo-Tam3 copy whose 5'-terminal region has been rearranged compared to the cognate Tam3 element, and NSt consists of two intact Tam3 copies in a head-to-head orientation. Neither locus interferes with the production of the intact Tam3 transposase (TPase) or the nuclear import of TPase. Both OSt and NSt produce specific sRNAs from their 5'-terminal regions containing multiple TPase-binding motifs. We performed sRNA induction experiments by TRV-mediated virus-induced gene silencing targeting the 5'-terminal region of the Tam3 sequence, which suppressed Tam3 transposition in the ost/nst plants. These results suggest that specific sRNAs can repress Tam3 transposition by interacting with the TPase-binding motifs within the Tam3 element or with the TPase itself.