Abstract
The seeds of a T-DNA insertion mutant of Arabidopsis, nekojita1 (nkj1), shifted germinable temperature limits lower than wild type. Abscisic acid (ABA) content in nkj1 seeds decreased to low levels by imbibition even at the restrictive temperature, 30 oC, as in germinating wild type seeds. Interestingly, nkj1 seeds were hyper-sensitive to ABA, and the germination was recovered by ABA biosynthesis inhibitor, fluridone, at the restrictive temperature. These results suggest that NKJ1 is a negative regulator of ABA signaling and has a promotive role on germination at permissive temperature conditions. nkj1 was mapped on the bottom arm of chromosome 4, and the gene was identified by sequencing of the T-DNA border and by genetic complementation test. The deduced amino acid sequence was highly homologous to Sec23/Sec24 subunit of COPII coat protein which is involved in vesicular transport from ER to golgi. NKJ1 gene expression was detected from various organs, and it was induced during germination and suppressed by restrictive high temperature conditions. We are now analyzing subcellular localization of NKJ1 protein by using transgenic plants which express NKJ1-GFP fusion protein.
