Retinoblastoma (RB) is the first identified tumor suppressor. Mutation in RB not only causes retinoblastoma, its mutation is also associated with many types of cancer. Hence, it is important to study how the RB pathway regulates cell division. Unfortunately, RB null mutants often lead to embryonic lethality in mammalian model systems such as mouse. It makes study of the RB pathway difficult. Also, lack of the RB pathway in the eukaryotic single-cell system, budding yeast, makes it unsuitable for this study. RB gene is also present in plants and its function is important for plant growth and development. Dr. Su-Chiung Fang's group at Agricultural Biotechnology Research Center and Biotechnology Center in Southern Taiwan, Academia Sinica, took the advantage of the powerful genetics of the unicellular microalga, Chlamydomonas reinhardtii (Chlamydomonas), to investigate how the RB pathway regulates cell division. Unlike other model systems, Chlamydomonas RB mutant is viable and divides supernumerously to generate tiny cells. The size suppression genetic screen has allowed them to identify a SMALL UBIQUITIN-LIKE MODIFIER (SUMO) protease as a novel downstream player of the RB. They further showed that the SUMO protease regulates SUMOylation of RIBOSOMAL PROTEIN L30 (RPL30) to control cell division. In RB mutant cells, the supernumerous cell division can be attenuated by increasing the amount of SUMOylated RPL30 protein (Figure 1). This finding reveals a novel mechanism through which SUMO conjugation regulates RPL30 to control cell division in RB mutant cells and suggests that RPL30 may be useful molecular target for anti-cancer drugs screening. This new insight is also fundamental for application of agricultural biotechnology. The lead author for this work is Yen-Ling Lin, a PhD student in Microbial Genomics PhD program of Academia Sinica-National Chung Hsing University in the Fang Lab. This study was funded by Academia Sinica Agricultural Biotechnology Research Center and the Ministry of Science and Technology. Article link：〈SUMO protease SMT7 modulates ribosomal protein L30 and regulates cell-size checkpoint function〉, http://www.plantcell.org/content/32/4/1285