Floral-like destiny induced by a galling Cecidomyiidae on the axillary buds of Marcetia taxifolia (Melastomataceae)

The galls induced by Cecidomyiidae, Diptera, are very diverse, with conspicuous evidence of tissue manipulation by the galling herbivores. Bud galls, as those induced by an unidentified Cecidomyiidae species on Marcetia taxifolia, Melastomataceae, can be considered as one of the most complex type of prosoplasma galls. The gall-inducer manipulate the axillary meristem of the plant in a way that gall morphogenesis may present both vegetative and reproductive features of the host plant. Herein, we analyzed traces of determinate and indeterminate growth in the bud gall of M. taxifolia, looking for parallels between the features of the leaves and flowers, natural fates of the meristematic cells. The bud galls are induced by the cecidomyiid fly, and are formed by the connation of eight leaf primordia, a common process in ovary morphogenesis. The bud gall corresponds to a pistil-shaped gall morphotype, with anatomical features similar to those of an hypanthium and sepals. The gall mimics an ovary, which has protective barriers at the apex, and a nutritive tissue (with storage of lipids and proteins) or a placenta, respectively, at the basal portion. The redifferentiation of the promeristem into a nutritive tissue at the base of the gall confers a determinate destiny to the axillary bud. Comparatively, the gradients of cell expansion and of accumulation of primary metabolites also indicate that the gall and the ovary are convergent structures. Some constraints of the host plant cells, such as the absence of lignification, and the accumulation of polyphenols, lipids and terpenoids, are not altered and may confer chemical protection for plant tissues and the larva against oxidative stress.