Previous studies have shown that Arabidopsis equilibrative nucleoside transporters (AtENTs) possess transport activities when produced in yeast cells and are differentially expressed in Arabidopsis organs. Herein, we report further analysis on the nucleoside transport activities and transcriptional patterns of AtENT members. The recombinant proteins of AtENTs 3, 6, and 7, but not those of AtENTs 1, 2, 4, and 8, were found to transport thymidine with high affinity. Contrary to previous suggestion that AtENT1 may not transport uridine, this work showed that recombinant AtENT1 was a pH-dependent and high-affinity transporter of uridine. When grown on MS plates, the AtENT3 knockout plants were more tolerant to the cytotoxic uridine analog 5-fluorouridine than wild-type plants and the knockout plants of AtENT1 or AtENT6. Consistent with this observation, the AtENT3 knockout line exhibited a significantly decreased ability to take up [ 3 H]uridine via the roots when compared with wild-type plants and the plants with mutated AtENT1 or AtENT6. This indicates that AtENT3, but not AtENTs 1 and 6, is the main transporter for uridine uptake in Arabidopsis roots. The transcription of AtENTs 1, 3, 4, 6, 7, and 8 was regulated in a complex manner during leaf development and senescence. In contrast, the six AtENT members were coordinately induced during seed germination. This work provides new information on the transport properties of recombinant AtENT proteins and new clues for future studies of the in vivo transport activities and physiological functions of the different ENT proteins in Arabidopsis plants.

Bacteria and archaea have evolved an adaptive immune system, known as type II prokaryotic clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) system, which uses short RNA to direct the degradation of target sequences present in invading viral and plasmid DNAs. Recent advances in CRISPR/Cas system provide an improved method for genome editing, showing robust and specific RNA-guided endonuclease activity at targeted endogenous genomic loci. It is the latest technology to modify genome DNA specifically and effectively following zinc finger nucleases (ZFNs) and TALE nucleases (TALENs). Compared with ZFNs and TALENs, CRISPR/Cas is much simpler and easier to engineer. This review summarizes recent progress, and discusses the prospects of CRISPR/Cas system, with an emphasis on its structure, principle, applications and potential challenges.