Abstract
Mitogen-activated protein kinase (MAPK) is one of the critical mediators of signaling systems by constituting phosphorylation pathways together with upstream kinases. Despite the importance, few direct targets have so far been identified, making it difficult to understand the whole features of so called MAPK cascade. Notably, a novel transcription factor, which was recently identified from tobacco, is activated upon phosphorylation by wound-induced protein kinase (WIPK), a typical MAPK in tobacco plants, and designated as NtWIF (Nicotiana tobacum WIPK interacting factor). To identify genes that are controlled by NtWIF, a microarray screening was performed using NtWIF overexpressing transgenic tobacco, and a set of affected clones were isolated. Approximately 28% of them were related to defense, confirming the critical role of WIPK in stress response. In addition, 15% of the clones were related to differentiation, suggesting pleiotrophic effects of NtWIF. When NtWIF was overexpressed or silenced by RNAi in tobacco plants, abnormal seed development and root growth were observed. Seeds of RNAi lines exhibited immature endosperm, resulting in germination failure. Root growth was retarded in both transgenic seedlings due to abnormal cell numbers in meristem. These results implicated the participation of phytohormones, of which function might be controlled by NtWIF. Since NtWIF possesses a B3-DNA binding motif, which specifically recognizes auxin-responsive elements found in many auxin-responsive genes, the present finding suggested that WIPK/NtWIF functions not only in stress response but also in developmental process through hormonal control.
