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 importinα and importinβ (α/β) 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 IMPαs and 18 IMPβs in Arabidopsis. The IMPα isoforms could be tracked back to a common ancestor, while the IMPβs derived from different ones. The majority of transport receptor genes were constitutively expressed. Intriguingly, AtIMPα5, 7, 8 and AtIMPβ5 were specifically expressed in different tissues. AtIMPβ3 was the sole receptor that was obviously modulated by exogenous phytohormones, whereas three IMPαs and five IMPβs exhibited responses to environmental stimuli. Furthermore, our RT-PCR data provided direct evidence that AtIMPα5, 8 and AtIMPβ5 are not pseudogenes and we also corrected the open reading frame annotation of AtIMPα8. 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.