Genes linked to X or Z chromosomes, which are hemizygous in the heterogametic sex, are predicted to evolve at different rates than those on autosomes. This “faster-X effect” can arise either as a consequence of hemizygosity, which leads to more efficient selection for recessive beneficial mutations in the heterogametic sex, or as a consequence of reduced effective population size of the hemizygous chromosome, which leads to increased fixation of weakly deleterious mutations due to genetic drift. Empirical results to date suggest that, while the overall pattern across taxa is complicated, systems with male-heterogamy show a faster-X effect attributable to more efficient selection, while the faster-Z effect in female-heterogametic taxa is attributable to increased drift. To test the generality of the faster-Z pattern seen in birds and snakes, we sequenced the genome of the Lepidopteran silkmoth Bombyx huttoni. We show that silkmoths experience faster-Z evolution, but unlike in birds and snakes, the faster-Z effect appears to be attributable to more efficient positive selection. These results suggest that female-heterogamy alone is unlikely to explain the reduced efficacy of selection on the bird Z chromosome. It is likely that many factors, including differences in overall effective population size, influence Z chromosome evolution.

SummaryLepidopterans as other insects have a very potent innate immune system, which basically comprises cellular and humoral defence mechanisms against bacterial and fungal infections. In lepidopterans, not much is known about the defence mechanisms against viral pathogens, such as baculoviruses. Here we show that small silk proteins of the domesticated silkworm, Bombyx mori, called seroins, act as antiviral agents against a baculovirus pathogen, Bombyx mori nucleopolyhedrovirus (BmNPV). Involvement of these proteins in the inhibition of baculovirus infection was revealed by estimating the viral load upon their dsRNA-mediated knockdown. Additionally, we found through antimicrobial assays that seroins are potent inhibitors of bacterial growth. Binding competition assays followed by antimicrobial assays showed that seroins bind to peptidoglycan, a cell wall component of bacteria. Analysis of bacterial load upon knockdown of seroins resulted in higher proliferation of bacteria. Phylogenetic analysis showed the recent origin of seroins in a few moth species and duplication only in Bombycids. The antiviral and antibacterial activity of seroins shown in this study using several biochemical and molecular biological assays provide strong evidence to characterize them as antimicrobial proteins. Hence, we hypothesize that seroins are potent candidates for use in development of transgene-based disease resistant silkworm strains.

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Water chestnut (2n = 48) is an aquatic plant of Trapaceae family, the fruits of which are nutritious and have medicinal properties. By selecting from Green Spineless and Red Spineless Biotypes for high TSS and yield from natural population, we developed Improved Red Spineless (IRS) and Improved Green Spineless (IGS) genotypes and registered at N.B.P.G.R as IC 642169 and IC 642170, respectively. These two improved varieties were analyzed with the well-known local varieties using 10 RAPDs and 10 ISSR primers. A total of 78.0 polymorphic fragments with an average PIC of 0.32 and 0.16 and an average MI of 1.48 and 1.09 were produced by the RAPD and ISSR markers, respectively. The dendrogram analysis based on individual and combined RAPD and ISSR markers has demonstrated that the new improved varieties are molecularly distinct from the locally popular varieties. Among four genotypes, the unique gene sequences in 550 bp and 800 bp DNA ladders identified by AP-4 primer and 600 bp DNA ladders identified by AP-32 primer are only found in IRS genotype as dimorphic bands and single band, respectively. Similarly, in IGS water chestnut, DNA fragments AP30-1250, and ISSR23-1500 & ISSR23-1350 are only found as single bands and dimorphic bands, respectively.