Abstract
VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT-A2) is a subspecies-forming gene that confers the long-glume and large-grain traits of tetraploid Polish wheat (Triticum polonicum; AABB) and hexaploid Xinjiang rice wheat (T. petropavlovskyi; AABBDD). Transcriptional activation of VRT-A2 due to a natural sequence variation in its Intron-1 region significantly enhances grain weight but also causes some basal spikelets to fail to completely develop, thus decreasing grain number per spike and yield. This yield penalty has presented a challenge for the use of VRT-A2 in breeding high-yield wheat. Here, we report the characterization of 2 regulatory modules that fine-tune VRT-A2 expression in bread wheat (T. aestivum): (i) the APETALA2/Ethylene Responsive Factor (AP2/ERF)-type transcription factor MULTI-FLORET SPIKELET1 (TaMFS1) represses VRT-A2 expression by recruiting a transcriptional corepressor and a histone deacetylase and (ii) the STRUCTURE-SPECIFIC RECOGNITION PROTEIN 1 (TaSSRP1) facilitates VRT-A2 activation by assembling Mediator and further RNA polymerase II. Deleting TaMFS1 triggered moderate upregulation of VRT-A2 results in significantly increased grain weight without the yield penalty. Our study thus provides a feasible strategy for overcoming the tradeoffs of pleotropic genes by editing their upstream transcriptional regulators.