BRC1 is likely not involved in imposing dormancy in latent grapevine buds, but it could contribute to establishing apical dominance relationships among woody buds upon its activation

The complex architecture and growth cycle of the grapevine bud presents a knowledge gap in understanding if or how apical dominance regulators apply to the distinct growth patterns of prompt buds, which regularly burst on the shoot, and latent bud, which remain dormant on the cane until the following spring. Tracking the expression of a grapevine homolog of BRANCHED1 (BRC1), a key regulator of axillary bud outgrowth in annuals, may shed light on this knowledge gap. Previous analyses identified a potential grapevine functional homolog VvBRC1 and suggested that BRC1-dependent apical dominance inhibits outgrowth of prompt bud. However, a detailed analysis of the potential participation of VvBRC1 and apical dominance in regulation of latent buds at any stage of complexed growth cycle is still lacking. Here we attempted to investigate whether and when VvBRC1 is involved in controlling bud break of latent buds-both on the shoot during the growing season and on the cane throughout the dormancy cycle. Our data suggest that while the bud-specific VvBRC1 regulates prompt bud outgrowth, (1) it does not regulate outgrowth of latent buds during their development or endodormancy cycle; and (2) a VvBRC1-regulated apical dominance mechanism may be established among woody buds upon bud activation.