Phages play a key role in the marine environment by regulating the transfer of energy between trophic levels and influencing global carbon and nutrient cycles. The diversity of marine phage communities remains difficult to characterize because of the lack of a signature gene common to all phages. Recent studies have demonstrated the presence of host-derived auxiliary metabolic genes in phage genomes, such as those belonging to the Pho regulon, which regulates phosphate uptake and metabolism under low-phosphate conditions. Among the completely sequenced phage genomes in GenBank, this study identified Pho regulon genes in nearly 40% of the marine phage genomes, while only 4% of nonmarine phage genomes contained these genes. While several Pho regulon genes were identified, phoH was the most prevalent, appearing in 42 out of 602 completely sequenced phage genomes. Phylogenetic analysis demonstrated that phage phoH sequences formed a cluster distinct from those of their bacterial hosts. PCR primers designed to amplify a region of the phoH gene were used to determine the diversity of phage phoH sequences throughout a depth profile in the Sargasso Sea and at six locations worldwide. phoH was present at all sites examined, and a high diversity of phoH sequences was recovered. Most phoH sequences belonged to clusters without any cultured representatives. Each depth and geographic location had a distinct phoH composition, although most phoH clusters were recovered from multiple sites. Overall, phoH is an effective signature gene for examining phage diversity in the marine environment.Marine viruses merit study not only because of their sheer abundance but also because of the critical roles they play in the Earth's biogeochemical cycles (11). The majority of these viruses are phages (viruses that infect bacteria). Because phages are host-specific predators that influence the composition of the bacterial community (9, 47), it is essential to understand the diversity of marine phages. Microscopy-based methods have only limited resolution for analyzing marine phage diversity, and therefore genetic methods are preferable. However, identification of phages in environmental samples is hampered by the lack of a single gene found in all phages (50). Nonetheless, some genes are shared within groups of phages, and these "signature genes" can be used as markers to examine the diversity of a phage group of interest (70). Several signature genes have been developed to examine the diversity of phages in the marine environment, including structural genes (61,64,86), replication genes (10, 33), and auxiliary metabolic genes (14,54,60,68,80).Auxiliary metabolic genes (AMGs) are phage-borne metabolic genes that were typically thought to be restricted to cellular genomes yet have been identified in phage genomes through sequencing (11). Numerous AMGs involved in photosynthesis, carbon metabolism, and nucleotide metabolism have been identified in marine phages (14,35,36,42,43,65,68,78,80). In addition, marine phages carry AMGs involved in nut...

To understand complex regulatory processes in multicellular organisms, it is critical to be able to quantitatively analyze protein movement and protein-protein interactions in time and space. During Arabidopsis development, the intercellular movement of SHORTROOT (SHR) and subsequent interaction with its downstream target SCARECROW (SCR) control root patterning and cell fate specification. However, quantitative information about the spatio-temporal dynamics of SHR movement and SHR-SCR interaction is currently unavailable. Here, we quantify parameters including SHR mobility, oligomeric state, and association with SCR using a combination of Fluorescent Correlation Spectroscopy (FCS) techniques. We then incorporate these parameters into a mathematical model of SHR and SCR, which shows that SHR reaches a steady state in minutes, while SCR and the SHR-SCR complex reach a steady-state between 18 and 24 hr. Our model reveals the timing of SHR and SCR dynamics and allows us to understand how protein movement and protein-protein stoichiometry contribute to development.DOI: http://dx.doi.org/10.7554/eLife.14770.001

To understand complex regulatory processes in multicellular organisms, it is critical to be able to quantitatively analyze protein movement and protein-protein interactions in time and space. During Arabidopsis development, the intercellular movement of SHORTROOT (SHR) and subsequent interaction with its downstream target SCARECROW (SCR) control root patterning and cell fate specification. However, quantitative information about the spatio-temporal dynamics of SHR movement and SHR-SCR interaction is currently unavailable. Here, we quantify parameters including SHR mobility, oligomeric state, and association with SCR using a combination of Fluorescent Correlation Spectroscopy (FCS) techniques. We then incorporate these parameters into a mathematical model of SHR and SCR, which shows that SHR reaches a steady state in minutes, while SCR and the SHR-SCR complex reach a steady-state between 18 and 24 hr. Our model reveals the timing of SHR and SCR dynamics and allows us to understand how protein movement and protein-protein stoichiometry contribute to development.