Dehiscent fruits in Brassicaceae and Papaveraceae: convergent morpho-anatomical features with divergent underlying genetic mechanisms.

BACKGROUND AND AIMS

Dry dehiscent fruits have independently evolved multiple times during angiosperm diversification. A striking example is the convergent evolution of Brassicaceae siliques and Papaveraceae pods, both formed by two fused carpels forming valves, that meet at a replum or replum-like structure. In both cases, valve separation occurs through a dehiscence zone at the valve margins in contact with the replum. In Arabidopsis, fruit development is regulated by transcription factors: FRUITFULL (FUL) ensures proper valve cell division, REPLUMLESS (RPL) specifies replum identity, and SHATTERPROOF (SHP1/2) genes pattern the dehiscence zone. SHP1/2 also regulate INDEHISCENT (IND) for lignified layer formation and ALCATRAZ (ALC) and SPATULA (SPT) for the non-lignified layer, with the network antagonized by APETALA2 (AP2), which influences replum formation and valve margin growth.

METHODS

Using previously published and new In situ RNA hybridization expression data, we evaluated how this network applies to basal eudicots.

KEY RESULTS

In Bocconia frutescens, homolog expression suggests conserved roles for FUL and AP2 in fruit wall proliferation, acting antagonistically to ALC and RPL homologs localized to the dehiscence zone. A role for STK homologs in dehiscence zone formation cannot be excluded, while the role of AG-like genes, the closest homologs of SHP during fruit development is unlikely.

CONCLUSIONS

Our findings indicate significant rewiring of the fruit developmental network between basal and core eudicots, underscoring the need for functional studies in non-eudicot species to validate this framework.