Targeted mutagenesis of BnaSTM leads to abnormal shoot apex development and cotyledon petiole fusion at the seedling stage in Brassica napus L.

The Arabidopsis homeodomain transcription factor () is crucial for shoot apical meristem (SAM) function, which cooperates with () () feedback regulation loops to maintain the homeostasis of stem cells in SAM. also interacts with the boundary genes to regulate the tissue boundary formation. However, there are still few studies on the function of in , an important oil crop. There are two homologs of in ( and ). In the present study, CRISPR/Cas9 technology was employed to create the stable site-directed single and double mutants of the genes in The absence of SAM could be observed only in the double mutants at the mature embryo of seed, indicating that the redundant roles of and are vital for regulating SAM development. However, different from Arabidopsis, the SAM gradually recovered on the third day after seed germination in double mutants, resulting in delayed true leaves development but normal late vegetative and reproductive growth in . The double mutant displayed a fused cotyledon petiole phenotype at the seedling stage, which was similar but not identical to the in Arabidopsis. Further, transcriptome analysis showed that targeted mutation of caused significant changes for genes involved in the SAM boundary formation (, , ). In addition, also caused significant changes of a sets of genes related to organogenesis. Our findings reveal that the plays an important yet distinct role during SAM maintenance as compared to Arabidopsis.