Two-way induction: how germ cells are differentiated in plants

Plant reproductive development, particularly germ cell initiation, has been a central topic in plant biology for decades. However, the mechanisms driving the spatiotemporal patterning of diploid and haploid germ cell differentiation remain insufficiently understood. This article introduces the “two-way induction model,” which explains how diploid germ cells are initiated from somatic cells and how these germ cells, in turn, influence surrounding somatic cells during early development. The model, initially proposed in the context of stamen development, highlights the dynamic interaction between inward (somatic to germ cells) and outward (germ cells to surrounding somatic) induction processes. Advances in molecular technologies, including gene expression profiling, small molecule labeling, and high-resolution imaging, now provide opportunities to empirically test this model. Moreover, I discuss the potential application of the “two-way induction model” across different plant groups, including bryophytes and pteridophytes, where research is currently limited. The insights gained from this model could reshape our understanding of plant reproduction and provide new directions for studying the evolutionary and developmental processes governing germ cell differentiation in multicellular plants.