Genome-wide profiling of developmental, hormonal or environmental responsiveness of the nucleocytoplasmic transport receptors in Arabidopsis.

Being poikilothermic and sessile organisms, plants have to respond quickly to changing environmental cues, and a higher order of gene regulation is required. The significance of nucleocytoplasmic transport via importinalpha and importinbeta (alpha/beta) has been exhibited in a wide spectrum of biological processes. However, most of these receptors have not been characterized as to which cellular or development processes are required and how their expression is regulated by environmental stimuli. Here we pursued a phylogenetic analysis and investigated the expression patterns of all 8 IMPalphas and 18 IMPbetas in Arabidopsis. The IMPalpha isoforms could be tracked back to a common ancestor, while the IMPbetas derived from different ones. The majority of transport receptor genes were constitutively expressed. Intriguingly, AtIMPalpha5, 7, 8 and AtIMPbeta5 were specifically expressed in different tissues. AtIMPbeta3 was the sole receptor that was obviously modulated by exogenous phytohormones, whereas three IMPalphas and five IMPbetas exhibited responses to environmental stimuli. Furthermore, our RT-PCR data provided direct evidence that AtIMPalpha5, 8 and AtIMPbeta5 are not pseudogenes and we also corrected the open reading frame annotation of AtIMPalpha8. These genome-wide profiling results not only widen our understanding of these transport receptors, but also provide strong evidence supporting the role of transport receptors in multiple signaling pathways and give us an insight into the further analysis of nucleocytoplasmic trafficking in Arabidopsis.