RESUMEN
RHO-related GTPases of plants (ROPs) are a class of signal transduction G proteins (alsoknown as GTP binding proteins) widely existing in plants. ROP proteins act as " molecular switches" toregulate the signal transduction process during cellular activities such as plant cell polarity regulation, plant morphological development, hormone level regulation, stress responses and many other life activitiesby shifting between inactive GDP-binding and active GTP-binding forms in the cells. In this review, thedomain structure, classification, the mechanism of activity regulation and biological functions of ROPproteins were summarize. Furthermore, ROP proteins from Arabidopsis, maize, rice and barley werephylogenetically analyzed. The results show that ROP proteins were classified into two types based on thedomain structure of the proteins. However, these ROP proteins were divided into 4 clades based on thesimilarity of protein sequences. Furthermore, the mechanism of ROP proteins as a molecular switchregulating various signaling pathways in cells, and the specific functions and mechanisms of ROPs in thepolarized growth of pollen tubes, root hairs and plant pavement cells and other stress responses werecharacterized. In addition, the research progress of the function of ROPs in plant hormones such as ABA, IAA and BR mediated signal transduction were described as well. At last, the unanswered questions suchas why different ROP proteins play distinct roles in the same signaling pathway and how ROPs coordinatedifferent signal pathways to jointly regulate a plant’ s development or physiological process werediscussed, which may shed light on future research.