Arabidopsis NAC domain proteins VND-INTERACTING1 and ANAC103 interact with multiple NAC domain proteins

The Arabidopsis thaliana NAM, ATAF1/2 and CUC2 (NAC) domain transcription factor VND-INTERACTING1 (VNI1) was previously isolated as an interacting factor of VASCULAR-RELATED NAC-DOMAIN PROTEIN7 (VND7), a key regulator of xylem vessel differentiation, in a yeast two-hybrid screening. Here, we characterized VNI1 and its closest homolog, ANAC103, at the molecular level. Both VNI1 and ANAC103 interacted in vitro not only with VND proteins but also with other NAC domain proteins, such as NAC1 and CUC2. A transient expression assay showed that both VNI1 and ANAC103 are transcriptional activators. ANAC103 promoter activity was detected in vascular tissues, as well as in the trichomes, guard cells, and margins of young leaves. These data suggest that VNI1 and ANAC103 promote the differentiation of various types of cells by modulating the transcriptional activities of a wide range of NAC domain transcription factors.