Recent studies have established that nuclear export of mRNAs is functionally coupled to different steps in gene expression processes, such as transcription, splicing, 3'-end formation and even translation. It is suggested that the manner in which individual mRNAs are transcribed and processed in the nucleus affects nuclear export and eventually their cytoplasmic fates, thus such inter-dependence could be especially important for the efficient expression of newly transcribed mRNAs, which are encoded on genes activated by different stimuli including various environmental stresses and developmental cues. Here we describe recently uncovered molecular mechanisms of the nuclear export of mRNA, in which the TREX (TRanscription-EXport) complex plays important roles of functionally connecting transcription, mRNA packaging and nuclear export.