In This Issue

AGRICULTURAL SCIENCES

Transgenic plastids escape via pollen in tobacco

In most crops, plastids such as chloroplasts and mitochondria are maternally inherited, and plastid DNA is excluded from pollen, which carries the male gametes. As a result, plastid transformation to introduce transgenes into plants could reduce the risk of unwanted gene transfer from fields with genetically modified plants to neighboring fields. Paternal chloroplast leakage can occur at a low level, although the rate at which it occurs has widely varied in published reports. Two separate studies by Stephanie Ruf et al. and Zora Svab and Pal Maliga confirm that paternal plastid transgene leakage occurs in tobacco plants. The authors of both studies introduced antibiotic resistance transgenes into the chloroplasts of plants used as pollen donors, crossed these with genetically similar nonresistant plants, and screened the offspring. Fewer than 1 of 10,000 seedlings gained resistance, a number that the authors believe is much higher than what is likely to appear under field conditions. Understanding the genetic control of plastid inheritance will facilitate the design of future transgenic crops and minimize the risk of plastid transgene escape via pollen. — F.A.

“Determining the transgene containment level provided by chloroplast transformation” by Stephanie Ruf, Daniel Karcher, and Ralph Bock (see pages 6998–7002)

and

“Exceptional transmission of plastids and mitochondria from the transplastomic pollen parent and its impact on transgene containment” by Zora Svab and Pal Maliga (see pages 7003–7008)

ENVIRONMENTAL SCIENCES

Microbial players interlinked in Black Sea's nitrogen cycle

Nitrogen is essential to all life forms, and its availability often holds the key to biological production in the oceans. Nitrification, the stepwise oxidation of ammonium to nitrite and then nitrate, plays a key role in the marine nitrogen cycle; it links the recycling of organic matter to the ultimate nitrogen loss from the system. However, exactly which microbes are responsible for this process has been heavily debated in the last few years. Recent studies have speculated that Crenarchaeota, which comprise ≈30% of oceanic picoplankton, could be more prolific nitrifiers than the previously known aerobic ammonia-oxidizing bacteria (AOB). Using gene expression analyses, Phyllis Lam et al. show that the ammonia monooxygenase gene subunit A (amoA) of Crenarchaeota is active in the Black Sea. Both ammonia-oxidizing crenarchaea and AOB are important nitrifiers. Crenarchaeal ammonia oxidizers are probably the main contributors of nitrite and nitrate in the lower oxic zone of the water column, whereas AOB perform the same task in the suboxic zone. Both groups provide the nitrite needed by the so-called anammox bacteria, which combine nitrite and ammonium to form nitrogen gas that is ultimately lost from the system. — B.T.

“Linking crenarchaeal and bacterial nitrification to anammox in the Black Sea” by Phyllis Lam, Marlene M. Jensen, Gaute Lavik, Daniel F. McGinnis, Beat Müller, Carsten J. Schubert, Rudolf Amann, Bo Thamdrup, and Marcel M. M. Kuypers (see pages 7104–7110)

EVOLUTION, GEOLOGY

The evolution of biting

Several adaptations were involved in the evolution of ancient tetrapods from an aquatic to a terrestrial lifestyle. One such adaptation, suction, is an efficient method of feeding in water, but it does not work well on land. Therefore, early terrestrial inhabitants would have had to develop a new means to capture prey, namely, biting. Molly Markey and Charles Marshall report that skeletal evidence of a bite emerged in the Devonian aquatic tetrapod Acanthostega. By developing a quantitative method to investigate skull sutures in fossils spanning water-to-land evolution, Markey and Marshall measured skulls of modern fish to correlate metrics such as interdigitation and sinuosity with the forces generated during suction feeding. Skull sutures were subsequently measured in several species of fish and tetrapods from the Devonian and Permian periods. In early fish, bones were found to be compressed at the rear of the skull and stretched at the front, consistent with suction; in land-based tetrapods, these forces were reversed. Analysis of Acanthostega revealed that, although it was adapted to an aquatic lifestyle, it likely captured prey by biting. The analysis suggests that tetrapods first evolved a bite before emerging as fully terrestrial animals. — K.M.

“Terrestrial-style feeding in a very early aquatic tetrapod is supported by evidence from experimental analysis of suture morphology” by Molly J. Markey and Charles R. Marshall (see pages 7134–7138)

PSYCHOLOGY

Cochlear implants help deaf patients integrate multisensory input

A surgically implanted neuroprosthesis, the cochlear implant, allows a severely deaf patient the ability to understand speech by directly stimulating functional auditory nerves inside the cochlea. Patients remain sensitive to noisy environments and may develop compensatory skills to overcome their difficulties. Julien Rouger et al. found that cochlear-implanted deaf patients are adept at integrating visual and auditory signals and as a result can speech-read better than their normal-hearing counterparts. The authors followed the performance of nearly 100 postlinguistically deafened patients during a longitudinal study that extended over 8 years after implantation. In both unisensory (visual or auditory) and bisensory (visuo-auditory) word recognition experiments, cochlear-implanted patients outperformed normal-hearing individuals who were presented with stimuli distorted to simulate the processing performed by the cochlear implant system. This work may help better guide the rehabilitation of patients using visually oriented therapeutic strategies. — F.A.

“Evidence that cochlear-implanted deaf patients are better multisensory integrators” by J. Rouger, S. Lagleyre, B. Fraysse, S. Deneve, O. Deguine, and P. Barone (see pages 7295–7300)