Abstract
Plants in the genus Asparagus have determinate leaf-like organs called cladodes in axils of degenerated foliage leaves. Because of their leaf-like morphology and axillary position, it has been unclear how cladodes have evolved and diversified. To reveal the evolutionary processes of cladodes, we have studied cladodes of A. asparagoides, which is sister to all other species in Asparagus and has leaf-like cladodes. The results indicated that cladodes are modified axillary shoots and the co-option of pre-existing genetic regulatory networks (GRN) involved in leaf development transferred the leaf-like form to axillary shoots. Moreover, to reveal the processes of the diversification, we also studied cladodes of A. officinalis, which has cylindrical cladodes. The results imply that altered expression pattern of leaf polarity genes led to the cylindrical morphology of cladodes in the A. officinalis clade. Thus, these results indicated that the co-option and alteration of pre-existing GRN play an important role in acquisition and subsequent morphological diversification of cladodes, respectively. We take the cladodes in the genus Asparagus as an example and discuss the acquisition and diversification of leaf-like organ.
