Is the 6 kDa tobacco etch viral protein a bona fide ERES marker?

The claim that the 6 kDa viral protein (VP) of Tobacco Etch Virus is a marker for ER exit sites (ERES) has been investigated. When transiently expressed as a CFP tagged fusion construct in tobacco mesophyll protoplasts, this integral membrane protein co-localizes with both the COPII coat protein YFP-SEC24 and the Golgi marker Man1-RFP. However, when over-expressed the VP locates to larger spherical structures which co-localize with neither ER nor Golgi markers. Nevertheless, deletion of the COPII interactive N-terminal D(X)E motif causes it to be broadly distributed throughout the ER, supporting the notion that this protein could be an ERES marker. Curiously, whereas brefeldin A (BFA) caused a typical Golgi-stack response (redistribution into the ER) of the VP in leaf epidermal cells, in protoplasts it resulted in the formation of structures identical to those formed by over-expression. However, anomalous results were obtained with protoplasts: when co-expressed with the non-cycling cis-Golgi marker Man1-RFP, a BFA-induced redistribution of the VP-CFP signal into the ER was observed, but, in the presence of the cycling Golgi marker ERD2-YFP, this did not occur. High resolution images of side-on views of Golgi stacks in epidermal cells showed that the 6 kDa VP-CFP signal overlapped considerably more with YFP-SEC24 than with Man1-RFP, indicating that the VP is proportionately more associated with ERES. However, based on a consideration of the structure of its cytoplasmic tail, the scenario that the VP collects at ERES and is transported to the cis-Golgi before being recycled back to the ER, is supported

Tubule-Guided Cell-to-Cell Movement of a Plant Virus Requires Class XI Myosin Motors

Cell-to-cell movement of plant viruses occurs via plasmodesmata (PD), organelles that evolved to facilitate intercellular communications. Viral movement proteins (MP) modify PD to allow passage of the virus particles or nucleoproteins. This passage occurs via several distinct mechanisms one of which is MP-dependent formation of the tubules that traverse PD and provide a conduit for virion translocation. The MP of tubule-forming viruses including Grapevine fanleaf virus (GFLV) recruit the plant PD receptors called Plasmodesmata Located Proteins (PDLP) to mediate tubule assembly and virus movement. Here we show that PDLP1 is transported to PD through a specific route within the secretory pathway in a myosin-dependent manner. This transport relies primarily on the class XI myosins XI-K and XI-2. Inactivation of these myosins using dominant negative inhibition results in mislocalization of PDLP and MP and suppression of GFLV movement. We also found that the proper targeting of specific markers of the Golgi apparatus, the plasma membrane, PD, lipid raft subdomains within the plasma membrane, and the tonoplast was not affected by myosin XI-K inhibition. However, the normal tonoplast dynamics required myosin XI-K activity. These results reveal a new pathway of the myosin-dependent protein trafficking to PD that is hijacked by GFLV to promote tubule-guided transport of this virus between plant cells

Survival of Female Scaled Quail During the Breeding Season at Three Sites in the Chihuahuan Desert

Scaled quail (Callipepla squamata) populations declined markedly across much of their range from 1988-2004, however little research has been conducted to investigate possible causes for the decline. As part of a larger study on scaled quail ecology and management, and in an attempt to determine whether breeding season survival could be implicated in this decline, we monitored survival of radiotagged female scaled quail during the breeding season at sites in Brewster and Pecos counties, Texas, and Sierra County, New Mexico, USA during 1999-2003. Survival rates were calculated using Kaplan Meier analysis for birds living \u3e7 days post capture. Interval survival rates (S) from Mar-Aug ranged from 0.46 to 0.82 for populations in Pecos County, Texas, and from 0.56 to 0.69 in Brewster County, Texas; survival was lower at the New Mexico site (S ranging from 0.22 to 0.48). Predation by mammals was the leading cause of mortality at both Texas study sites, whereas predation by raptors was the primary cause of mortality at the New Mexico site. Several mortalities in Texas were attributed to drowning; 3 in a water trough and 2 others following a flash flood. Survival rates on Texas sites were not affected by moist soil management but were greater than survival on New Mexico sites. Survival on New Mexico sites was greater on areas with access to free-choice quail feeders (S = 0.48) relative to a non-fed site (S = 0.22). Survival rates of scaled quail during the breeding season were higher than those reported for radiotagged northern bobwhite in west Texas at similar latitudes. Survival of female scaled quail during the breeding season does not appear to be a bottleneck to recruitment, at least not on sites where conservative grazing management is practiced