Domestication‐medicated erect growth confines soybean basal branching by upregulating <i>GmBRC1a</i> and <scp> <i>GmBRC1b</i> </scp>

Soybean domestication has led to a remarkable transformation from the prostrate, vining growth pattern of wild soybeans to the erect growth habit characteristic of modern cultivars. Despite this significant morphological shift, the intricate molecular mechanisms governing the alteration in shoot architecture during domestication remain elusive. Here, we integrated transcriptomic, biochemical, and genetic approaches to dissect the regulatory mechanism underlying basal node branching during the transition of stem growth habit in soybean domestication. We found that the erect growth habit of cultivated soybean restricts basal node branching and reduces cytokinin levels. Exogenous cytokinin application to cultivated soybean enhances basal branching. GmBRC1b is specifically expressed in cotyledonary buds and node 1 buds, and its expression is suppressed by cytokinin. Knocking out GmBRC1a and GmBRC1b increases basal branching and yield, in part, by activating SPL (SQUAMOSA promoter-binding protein-like) transcription factors. Evolutionary analysis reveals that GmBRC1a/b genes underwent artificial selection during domestication, causing their expression to rise over time. Our study reveals that the erect growth habit in cultivated soybeans restricts basal branching via the cytokinin-GmBRC1 module, clarifying the genetic basis of shoot architectural evolution during domestication and highlighting the role of basal branching regulation in crop improvement.