Ubiquitination is emerging as a tight regulatory mechanism that is necessary for all aspects of development and survival of all eukaryotes. Recent genomic and genetic analysis in Arabidopsis suggests that ubiquitination may also play important roles in plant response to the phytohormone abscisic acid (ABA). Many components of the ubiquitination pathway, such as ubiquitin-conjugating enzyme E2, ubiquitin ligase E3 and components of the proteasome, have been identified or predicted to be essential in ABA biosynthesis, catabolism and signaling. In addition, the ubiquitination-related pathway, sumoylation, is also involved in ABA signaling. We summarize in this report recent developments to elucidate their roles in the ABA-related pathway.Author for correspondence. Tel (Fax): +86 (0)10 6488 9351; E-mail: qxie@genetics.ac.cn