Metabolic rate and growth in the temperate bivalve Mercenaria mercenaria at a biogeographic limit, from the English Channel

Metabolism and growth rate of the hard clam, Mercenaria mercenaria, were investigated in a population invasive to Southampton Water, southern England. An individual metabolic model expressed as a function of soft tissue dry mass was fitted to data of 18 individuals (log (VO2) = −1.952 + 0.543 • log (DM); F1,16 = 201.18, P < 0.001, r2 = 0.926). A von Bertalanffy growth function was fitted to 227 size-at-age data pairs of 18 individuals (Ht = 80.13 • (1 − e−0.149 • (t−0.542)); r2 = 0.927). Individual age-specific somatic production was calculated, demonstrating increase with age to a maximum of 3.88 kJ y−1 at ten years old followed by decrease, and individual age-specific annual respiration was calculated, demonstrating asymptotic increase with age to 231.37 kJ y−1 at 30 years old. Results found here lie within the physiological tolerances reported across the biogeographical range, suggesting that the species' biogeographical limitation in the UK to Southampton Water results from ecological rather than physiological factors

A mobile signal transported over a long distance induces systemic transcriptional gene silencing in a grafted partner

Transcriptional gene silencing (TGS) can be induced by promoter-targeted small interfering RNA (siRNA). Long-distance transmission of TGS by viral infection in plants has been reported. However, systemic TGS has not been observed in the case of using an inverted repeat transgene as the silencing trigger. Here it is reported that a mobile signal, presumably the siRNA, produced from a hairpin structure transgene controlled by a companion cell-specific promoter can also induce transmissible TGS in both a modified agroinfiltration and a grafting system. Although the transmissible TGS occurred only in cells located in the vicinity of a leaf vein in the scion, very strong silencing was observed in the root system, especially the lateral roots, including the root apical meristem. The transmissible TGS was maintained through tissue culture and subsequently inherited by the progeny. The results suggest the potential application of mobile promoter-targeting siRNA in horticulture for improvement of plant cultivars by grafting