Ontogeny of postgenital leaf sheath fusion in Commelina erecta L. (Commelinaceae)

MAIN CONCLUSION: Commelina erecta L. leaf sheaths fuse postgenitally without KN1 ortholog expression, indicating a distinct molecular mechanism for sheath fusion in Commelinaceae, contrasting it from sheath formation in Poaceae. Leaf sheaths are common structures within monocotyledonous, being open or closed depending on the separation of their margins. In Commelinaceae, a family of monocotyledonous plants with simple leaves and alternate phyllotaxy, their sheaths are closed. In Poaceae, which often have open sheaths, there has been evidence of KNOX genes affecting the fusion in sheaths in this family. The present study, therefore, investigated the nature of the sheath fusion and the expression of KN1 ortholog at the leaf sheaths in Commelina erecta L. Samples of the shoot apex and leaf primordia were subjected to scanning electron microscopy and optical microscopy techniques with serial sections in paraffin. Samples of apical meristems from specimens of C. erecta were also subjected to in situ hybridization to verify the expression of KNOX within its leaves, with the probe sequence established by degenerate RT-PCR. The anatomical analysis revealed that sheaths of C. erecta undergo post-genital fusion. In situ hybridizations in C. erecta revealed no expression of KN1 ortholog at the region of the fused sheath margins. The post-genital fusion indicates, therefore, the previous separation of the sheath margins, which, associated with lack of expression of KN1 at this region, suggests a distinct molecular mechanism of leaf fusion in Commelinaceae, contrasting it from sheath formation in Poaceae.