BbrizAGL6 Is Differentially Expressed During Embryo Sac Formation of Apomictic and Sexual Brachiaria brizantha Plants

Species of the genus Brachiaria comprise plants with different modes of reproduction, sexual and apomictic. In apomixis, the embryo sac differentiates from an unreduced cell, and the embryo develops in the absence of egg cell fertilisation. In this work, the characterisation and expression analyses of a MADS-box gene from Brachiaria brizantha, named BbrizAGL6, was described in sexual and apomictic plants. Phylogenetic analyses indicated that BbrizAGL6 belongs to the AGL6-like subfamily of proteins and clusters together with the AGL6-like protein of other monocots. BbrizAGL6 and AGL6 show conservation of the protein complex. Furthermore, BbrizAGL6 expressed preferentially in reproductive tissues and corresponding transcripts were detected in anthers and ovules. In ovules of B. brizantha, where the main differences among sexual and apomictic reproduction occur, BbrizAGL6 was differentially modulated. Transcripts of BbrizAGL6 were localised in the megaspore mother cell of ovaries from apomictic and sexual plants and, additionally, in the region where aposporic initial cells differentiate, in the nucellus of apomictic plants. For the first time, a role of an AGL6-like gene in megasporogenesis of apomictic and sexual plants is suggested.