Common evolutionary origin of the central portions of the Ri TL-DNA of Agrobacterium rhizogenes and the Ti T-DNAs of Agrobacterium tumefaciens

Analysis of published sequences for Ri TL-DNA (root-inducing left-hand transferred DNA) of Agrobacterium rhizogenes revealed several unsuspected structural features. First, Ri TL-DNA genes are redundant. Using redundancy as a criterion, three regions (left, middle and right) were discerned. The left one, ORFs (open reading frames) 1–7, contains no detectable redundancy. In the middle region a highly diverged gene family was detected in ORFs 8, 11, 12, 13 and 14. The right region contains an apparently recent duplication (ORF 15 =18+17). We interpret the phenomenon of redundancy, particularly in the central region that encodes the transformed phenotype, to be an adaptation that ensures function in a variety of host species. Comparison of Ri TL-DNA and Ti T-DNAs from Agrobacterium tumefaciens revealed common structures, unpredicted by previous nucleic acid hybridization studies. Ri TL-DNA ORF 8 is a diverged Ti T-DNA tms1. Both Agrobacterium genes consist of a member of the diverged gene family detected in the central part of the Ri TL-DNA, but fused to a sequence similar to iaaM of Pseudomonas savastonoi. Other members of this gene family were found scattered throughout Ti T-DNA. We argue that the central region of Ri and the part of Ti T-DNA including ORFs 5–10 evolved from a common ancestor. We present the hypothesis that the gene family encodes functions that alter developmental plasticity in higher plants.     

Glutamine-dependent signaling controls pluripotent stem cell fate

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Metabolic plasticity drives development during mammalian embryogenesis

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Sinistral snail shells in the sea: developmental causes and consequences

The paucity of sinistral (left-coiling) relative to dextral (right-coiling) species of gastropods in the marine realm is an enigma. In Conus , one of the most diverse marine animal genera, sinistral shell coiling has evolved as a species-wide character only once. Fossils of this species, Conus adversarius , are found in Upper Pliocene and lowermost Pleistocene deposits in the southeastern USA. Conus adversarius had nonplanktonic larval development; this may have been a critical factor for the early establishment of the species, as well as sinistral marine species in other clades. Notably, most specimens of aberrantly sinistral modern Conus are derived from typically dextral species that have nonplanktonic development. If C. adversarius was reproductively isolated from dextral conspecifics, then this species may provide an example of nearly instantaneous sympatric speciation in the fossil record. Furthermore, the common and widespread – while geologically short-lived – fossil shells of C. adversarius show large amounts of variability in form and this variation may be related, at least in part, to a pleiotropic effect associated with the reversed coiling direction of this species.     

Within-tree spatial variation in the leaf monoterpenes of Sequoia sempervirens

Location within a tree was analyzed as a source of variation in Sequoia sempervirens leaf monoterpenes. No differences were found for quantitative composition or total yield/dry wt among lower, middle and upper canopy positions. The awlshaped, spirally arranged leaves of vigorous upper shoots showed small quantitative compositional differences, but not differences in total yield. The intermediate leaf form of young sprouts had the most different monoterpene quantitative composition and about three times the total yield of the above two leaf forms. Analysis of a clonal ring of 17 adult trees resulted in coefficients of variation similar to those for samples collected from different canopy levels of the same shoot. Results revealed the sources and magnitudes of experimental error in comparative studies of this species' leaf monoterpenes, and did not support the concept that somatic mutation provides an important source of variation in a large, long-lived organism such as coast redwood.     

Adaptive developmental plasticity: what is it,how can we recognize it and when can it evolve?

Developmental plasticity describes situations where a specific input during an individual''s development produces a lasting alteration in phenotype. Some instances of developmental plasticity may be adaptive, meaning that the tendency to produce the phenotype conditional on having experienced the developmental input has been under positive selection. We discuss the necessary assumptions and predictions of hypotheses concerning adaptive developmental plasticity (ADP) and develop guidelines for how to test empirically whether a particular example is adaptive. Central to our analysis is the distinction between two kinds of ADP: informational, where the developmental input provides information about the future environment, and somatic state-based, where the developmental input enduringly alters some aspect of the individual''s somatic state. Both types are likely to exist in nature, but evolve under different conditions. In all cases of ADP, the expected fitness of individuals who experience the input and develop the phenotype should be higher than that of those who experience the input and do not develop the phenotype, while the expected fitness of those who do not experience the input and do not develop the phenotype should be higher than those who do not experience the input and do develop the phenotype. We describe ancillary predictions that are specific to just one of the two types of ADP and thus distinguish between them.