Figure 4.

Model illustrating the spatiotemporal expression patterns of the auxin response factors (ARFs) during various stages of syncytium development. During the syncytium initiation phase, ARF3, 6, 10–12, 14, 15 and 20–22 are predominantly expressed in the initial feeding cells, whereas ARF1, 2, 4, 5, 7, 9 and 17–19 are strongly activated in both the syncytial cells and in neighbouring cells. ARF2, 5 and 18 have an expanded expression pattern, which most probably marks the axis of expanding syncytium. During the syncytium formation phase, ARF1, 2, 5, 7, 17 and 18 continue to exhibit high expression in the developing syncytium. During the syncytium maintenance phase, only ARF1–3, 7, 17 and 20–22 are expressed in fully developed syncytium.