TINod (Transcription Initiator for Nodulation), a New GRAS Family Transcription Factor of Lotus japonicus, Initiates Transcription in Analogous Manner to STAT of Animals

Abstract

On infection with Mesorhizobium loti, the nod- mutant of Lotus japonicus, tinod can induce calcium spiking and root hair deformation, but cannot form infection threads or start cortical cell division. The mutant was also blocked in induction of early nodulins, like ENOD40 and NIN by M. loti. We have positionally cloned the causal gene, TINod, encoding a novel member of plant-specific transcription factor GRAS family. Expression of TINod was restricted only to roots, especially in their stele, and was suppressed rapidly upon inoculation with M. loti, suggesting that TINod is functioning on the downstream of calcium spiking, as a surveillance factor of rhizobial infection to initiate transcription of several nodulation-related genes. Most interestingly, TINod was first, as the plant GRAS members, shown to function analogously with animal STATs (Signal Transducers and Activators of Transcription) in its SH2 domain, which have been known to be conserved in both families.