Characterization of photosystem 1 chlorophyll a/b-binding apoprotein accumulation in developing soybean using type-specific antibodies.

The structure and supramolecular assembly of the soybean photosystem 1 (PS 1) chlorophyll a/b-binding antenna (LHC 1) was examined. We identified the subunit composition of LHC 1 in soybean and followed the accumulation of individual subunits during light-induced assembly. We observed four LHC 1 subunits, at 23, 22, 21 and 20.5 kDa, obtained partial sequence information by amino-terminal sequence analysis, and classified the 20.5, 22, and 21 kDa subunits as being encoded by type I, II, and IV chlorophyll a/b binding protein genes, respectively. Antisera against LHC 1 subunits were used to follow the accumulation of individual subunits during the light-initiated transition from etioplast to chloroplast. Several points are noteworthy. First, monospecific antibody against the 22 kDa subunit decorated a 25 kDa peptide in etiolated tissue, which declined during maturation. This decline correlated with the light-induced appearance of mature 22 kDa peptide, suggesting a precursor/product relationship. Second, the same antibody identified a 22 kDa protein in mature corn, but not a larger band in etiolated corn, suggesting that LHC 1 accumulation is regulated differently between species before the onset of chlorophyll biosynthesis. Third, the mature 22 kDa subunit appeared somewhat later than the other LHC 1 peptides during greening, implying that this subunit is less intimately associated with the PS1 core than are the subunits appearing earlier in development.     

PATTERNS OF CELL SIZE CHANGE IN A MARINE CENTRIC DIATOM: VARIABILITY EVOLVING FROM CLONAL ISOLATES1

Isolates of the centric diatom, Thalassiosira weissflogii Grun., were maintained in exponential growth under constant, favorable conditions for nearly 2 years. During this interval, each culture underwent periodic increases and decreases in mean cell size, a behavior predicted for diatom populations alternating between sexual and asexual reproduction, respectively. The overall patterns of cell size change displayed by each culture, however, were unique. The maximum size of newly enlarged cells varied among isolates and within a given isolate over time. Consequently, both the timing and rate of increase in mean cell size also varied despite the fact that the minimum average cell size obtained by the various cultures was relatively constant. The most consistent feature among the isolates was the rate of decrease in mean cell size, a value determined by the physical constraints of the diatom frustule during mitotic divisions. We hypothesize that the extent of the variability exhibited by these cultures results from the fact that an inherent feature of diatom populations is a constantly changing genetic composition.     

Identification of a New Gene Family Expressed during the Onset of Sexual Reproduction in the Centric Diatom Thalassiosira weissflogii

An intriguing feature of the diatom life cycle is that sexual reproduction and the generation of genetic diversity are coupled to the control of cell size. A PCR-based cDNA subtraction technique was used to identify genes that are expressed as small cells of the centric diatom Thalassiosira weissflogii initiate gametogenesis. Ten genes that are up-regulated during the early stages of sexual reproduction have been identified thus far. Three of the sexually induced genes, Sig1, Sig2, and Sig3, were sequenced to completion and are members of a novel gene family. The three polypeptides encoded by these genes possess different molecular masses and charges but display many features in common: they share five highly conserved domains; they each contain three or more cysteine-rich epithelial growth factor (EGF)-like repeats; and they each display homology to the EGF-like region of the vertebrate extracellular matrix glycoprotein tenascin X. Interestingly, the five conserved domains appear in the same order in each polypeptide but are separated by variable numbers of nonconserved amino acids. SIG1 and SIG2 display putative regulatory domains within the nonconserved regions. A calcium-binding, EF-hand motif is found in SIG1, and an ATP/GTP binding motif is present in SIG2. The striking similarity between the SIG polypeptides and extracellular matrix components commonly involved in cell-cell interactions suggests that the SIG polypeptides may play a role in sperm-egg recognition. The SIG polypeptides are thus important molecular targets for determining when and where sexual reproduction occurs in the field.     

Veiled cinema: A conversation with Yousry Nasrallah

This interview with Yousry Nasrallah introduces an increasingly important Egyptian director to American audiences through his latest film, On Boys, Girls, and the Veil. The film is a documentary about a phenomenon sometimes misleadingly called “the veil” by Westerners. Nasrallah's film discusses relations between men and women through their own conversations about the wearing of clothes designed to restrict vision. The interview relates Nasrallah's work to the larger tradition of Egyptian filmmaking.     

Rapid Evolution of a Sexual Reproduction Gene in Centric Diatoms of the Genus Thalassiosira

Sexual reproduction is commonly assumed to occur in the vast majority of diatoms due to the intimate association of this process with cell size control. Surprisingly, however, little is known about the impact of sexual events on diatom population dynamics. The Sig1 gene is strongly upregulated during sexual reproduction in the centric diatom Thalassiosira weissflogii and has been hypothesized to encode a protein involved in gamete recognition. In the present study, degenerate PCR primers were designed and used to amplify a portion of Sig1 from three closely related species in the cosmopolitan genus Thalassiosira, Thalassiosira oceanica, Thalassiosira guillardii, and Thalassiosira pseudonana. Identification of Sig1 in these three additional species facilitated development of this gene as a molecular marker for diatom sexual events. Examination of the new sequences indicated that multiple copies of Sig1 are probably present in the genome. Moreover, compared to the housekeeping gene β-tubulin, the Sig1 genes of isolates of T. weissflogii collected from different regions of the Atlantic and Pacific oceans displayed high levels of divergence. The Sig1 genes of the four closely related Thalassiosira species also displayed high levels of sequence divergence compared to the levels observed with a second gene, Fcp, probably explaining why Sig1 could not be amplified from more distantly related species. The high levels of sequence divergence both within and between species suggest that Sig1 is rapidly evolving in a manner reminiscent of the manner observed in other genes that encode gamete recognition proteins. A simple model is presented for Sig1 evolution and the implications of such a rapidly evolving sexual reproduction gene for diatom speciation and population dynamics.     

Superovulation and embryo recovery from peripubertal Holstein heifers

The use of peripubertal donors in embryo transfer (ET) programs presents significant opportunity to accelerate genetic gain in domestic livestock by reducing the generation interval. These studies were designed to evaluate feasibility of superovulation and embryo recovery in peripubertal heifers (starting at 7.8 months of age), and to determine whether subsequent reproductive and lactational performance of donor heifers were impaired. Study 1 utilized 10 pairs of contemporary full-sibling heifers in which one heifer in each pair was assigned to receive a superovulation regimen and her full-sibling contemporary received placebo. Treated heifers were artificially inseminated at estrus and embryos were flushed transcervically 4-6 days later. Based on recovery of oocytes and/or embryos, 9 of 10 heifers responded to the hormonal regimen and 12 total embryos were recovered. Seven embryos (58%) were transferred into recipients resulting in five pregnancies. Control and treated heifers remained in the herd and were bred at a natural estrus by AI at 15 months of age. Lactation records, i.e., 305 days mature equivalent (305 d ME) were obtained, and all animals were evaluated for udder conformation traits between 32 and 38 months of age. Reproductive traits (age at first calving and days to conception) and lactational traits of heifers subjected to embryo transfer and their non-treated full-siblings did not differ (P > 0.05). Study 2 was conducted to establish the commercial feasibility of hormonally programming peripubertal heifers ranging in age from 7.8 to 9.9; 10 to 11.9; 12 to 13.9 and >/= 14 months. In total, 3982 embryos were recovered from 520 heifers, with 2419 (60.7%) of those categorized as viable (transferable). The number of ova/embryos obtained per flush (5.6 +/- 1.0) and the number of transferable embryos (2.8 +/- 0.5) was reduced (P < 0.05) in heifers of age 7.8-9.9 months compared to all other age groups. There was no difference (P > 0.05) in the number of ova/embryos recovered (7.8 +/- 0.3), or the number of transferable embryos (4.8 +/- 0.2), among heifers that were >/=10 months of age. The number of unfertilized ova did not differ by age, however, more degenerate embryos tended to be recovered from heifers <10 months of age compared to heifers >/=14 months of age. These data indicate that transferable embryos can be safely recovered from heifers beginning at 10 months of age without compromising subsequent reproductive or lactational performance of the donor.     

Interactions between Diatoms and Bacteria

Summary: Diatoms and bacteria have cooccurred in common habitats for hundreds of millions of years, thus fostering specific associations and interactions with global biogeochemical consequences. Diatoms are responsible for one-fifth of the photosynthesis on Earth, while bacteria remineralize a large portion of this fixed carbon in the oceans. Through their coexistence, diatoms and bacteria cycle nutrients between oxidized and reduced states, impacting bioavailability and ultimately feeding higher trophic levels. Here we present an overview of how diatoms and bacteria interact and the implications of these interactions. We emphasize that heterotrophic bacteria in the oceans that are consistently associated with diatoms are confined to two phyla. These consistent bacterial associations result from encounter mechanisms that occur within a microscale environment surrounding a diatom cell. We review signaling mechanisms that occur in this microenvironment to pave the way for specific interactions. Finally, we discuss known interactions between diatoms and bacteria and exciting new directions and research opportunities in this field. Throughout the review, we emphasize new technological advances that will help in the discovery of new interactions. Deciphering the languages of diatoms and bacteria and how they interact will inform our understanding of the role these organisms have in shaping the ocean and how these interactions may change in future oceans.