Functional analysis of a rice importin-α binding protein

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To identify novel nuclear proteins that are involved in plants' responses to light environment, the author analyzed the function of a candidate protein, named IABP4, that had been isolated by its binding to rice importin-α1a(IMPα1a), a component of nuclear transport machinery, whose expression is strong in the dark and is down-regulated by light. The obtained results are as follows.1.Gene expression and the effect of light : Similar to rice IMPα1a gene, the expression of IABP4 was down-regulated by light both in etiolated-and green-seedlings of rice and Arabidopsis. The result suggests that nuclear accumulation of IABP4 might be reduced in the dark as a result of reduced IABP4 protein level as well as reduced nuclear import of IAB P4.2.Functional analysis by knockout lines : Five knockout lines of IABP4 were identified in Arabidopsis, and the proportion of seedlings with open hook and cotyledons in the dark was higher in the knockouts than in wild type, suggesting that IABP4 protein may be suppressing photomorphogenesis in the dank. Because germinated seedlings were all hetero-zygous with respect to T-DNA insertion, the homozygote is considered to be embryonic lethal or unable to germinate, suggesting that IABP4 is not only involved in the control of photomorphgenesis but also essential for plants.3.IntraceMar localization and the effect of light: Though we obtained IABP4 antiserum, it contained antibodies to other plant proteins, so we could not use it for localization studies. By purifying antibody or by using GFP-fusion, examination of nuclear localization of IABP4 is urgently required.