The role of post-Golgi transport pathways and sorting motifs in the plasmodesmal targeting of the movement protein (MP) of Ourmia melon virus (OuMV)

Natali Ozber; Paolo Margaria; Charles T. Anderson; Massimo Turina; Cristina Rosa

Glycine substitutions in the Y motif altered the intracellular distribution of MP. A key question emerging from this observation is whether the Y motif in OuMV MP is a functional internalization motif. Y motifs are recognized by μ-subunits of APs 1-4 (Bonifacino and Traub, 2003) . In plants, CME of plasma membrane proteins depends on Y motifs in their cytoplasmic domains to be recognized by AP2M (Di Rubbo et al., 2013; Fan et al., 2013; Kim et al., 2013; Yamaoka et al., 2013) and it has been previously shown that CaMV MP is able to bind Arabidopsis AP2µ through three Y motifs (Carluccio et al., 2014) . Unlike CaMV MP, we failed to see direct binding of . CC-BY-NC-ND 4.0 International license is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/724716 doi: bioRxiv preprint AP2M to OuMV MP in vitro (Fig. 7) . Additionally, we did not observe any changes in the infectivity of OuMV in the absence of AP2M in Arabidopsis (Table 2) . It is, however, known that AP2M is not the sole regulator of CME in plants; a CME adaptor complex, TPLATE complex (TPC), is involved in the initiation of CME and is thus crucial for recruitment of clathrin and AP2 (Gadeyne et al., 2014) . Moreover, AP2 subunits are considered to form partially active complexes in the absence of single subunits (Wang et al., 2016) . Hence, other AP2 subunits and/or TPC may be important for internalization of OuMV MP, and in turn for infectivity of OuMV. At this point, we do not have enough evidence that the internalization of OuMV MP directly depends on AP2M.