The BIG gene controls size of shoot apical meristems in Arabidopsis thaliana

Key message BIG regulates the shoot stem cell population. Abstract The shoot apical meristem (SAM) contains a population of self-renewing cells, and provides daughter cells for initiation and development of aerial parts of plants. However, the underlying mechanisms of SAM size regulation remain largely unclear. Here, we identified a mutant that displayed a large SAM, designated big-shoot meristem ( big-m ), in Arabidopsis thaliana . The phenotype of big-m is caused by a new T-DNA insertion allele of BIG , causing a loss of function. The big-m mutant had more stem cells in the SAM than in the wild type. Expression of WUSCHEL ( WUS ) and SHOOTMERISTEMLESS ( STM ) was promoted in big-m compared with the wild type, showing that BIG functions upstream of WUS and STM . Therefore, BIG is an important regulator of the stem cell population in the SAM. Furthermore, genetic analysis indicated that BIG acts synergistically with PIN-FORMED1 (PIN1) in controlling SAM size. Our results suggest that BIG plays an important role in controlling Arabidopsis thaliana SAM growth via PIN1-mediated auxin homeostasis.