Two major conducting tissues in plants, phloem and xylem, are composed of highly specialized cell types adapted to long distance transport. Sieve elements (SEs) in the phloem display a thick cell wall, callose-rich sieve plates and low cytoplasmic density. SE differentiation is driven by selective autolysis combined with enucleation, after which the plasma membrane and some organelles are retained. By contrast, differentiation of xylem tracheary elements (TEs) involves complete clearance of the cellular components by programmed cell death followed by autolysis of the protoplast; this is accompanied by extensive deposition of lignin and cellulose in the cell wall. Emerging molecular data on TE and SE differentiation indicate a central role for NAC and MYB type transcription factors in both processes. ; Other ; The Y.H. laboratory is funded by the Academy of Finland Centre of Excellence programme, the Gatsby Foundation, the Biotechnology and Biological Sciences Research Council, the University of Helsinki, the European Research Council Advanced Investigator Grant Symdev (No. 323052) and Tekes (the Finnish Funding Agency for Technology and Innovation).