Identification of FAM96B as a novel prelamin A binding partner

Prelamin A accumulation causes nuclear abnormalities, impairs nuclear functions, and eventually promotes cellular senescence. However, the underlying mechanism of how prelamin A promotes cellular senescence is still poorly understood. Here we carried out a yeast two-hybrid screen using a human skeletal muscle cDNA library to search for prelamin A binding partners, and identified FAM96B as a prelamin A binding partner. The interaction of FAM96B with prelamin A was confirmed by GST pull-down and co-immunoprecipitation experiments. Furthermore, co-localization experiments by fluorescent confocal microscopy revealed that FAM96B colocalized with prelamin A in HEK-293 cells. Taken together, our data demonstrated the physical interaction between FAM96B and prelamin A, which may provide some clues to the mechanisms of prelamin A in premature aging.     

MUTATIONAL MELTDOWN IN SELFING ARABIDOPSIS LYRATA

The majority of plant species and many animals are hermaphrodites, with individuals expressing both female and male function. Although hermaphrodites can potentially reproduce by self‐fertilization, they have a high prevalence of outcrossing. The genetic advantages of outcrossing are described by two hypotheses: avoidance of inbreeding depression because selfing leads to immediate expression of recessive deleterious mutations, and release from drift load because self‐fertilization leads to long‐term accumulation of deleterious mutations due to genetic drift and, eventually, to extinction. I tested both hypotheses by experimentally crossing Arabidopsis lyrata plants (self‐pollinated, cross‐pollinated within the population, or cross‐pollinated between populations) and measuring offspring performance over 3 years. There were 18 source populations, each of which was either predominantly outcrossing, mixed mating, or predominantly selfing. Contrary to predictions, outcrossing populations had low inbreeding depression, which equaled that of selfing populations, challenging the central role of inbreeding depression in mating system shifts. However, plants from selfing populations showed the greatest increase in fitness when crossed with plants from other populations, reflecting higher drift load. The results support the hypothesis that extinction by mutational meltdown is why selfing hermaphroditic taxa are rare, despite their frequent appearance over evolutionary time.     

Comparisons of the thermal physiology of water hyacinth biological control agents: predicting establishment and distribution pre‐ and post‐release

Investigations into the thermal physiology of weed biological control agents may elucidate reasons for establishment failure following release. Such studies have shown that the success of water hyacinth biological control in South Africa remains variable in the high‐lying interior Highveld region, because the control agents are restricted to establishment and development due to extreme winter conditions. To determine the importance of thermal physiology studies, both pre‐ and post‐release, this study compared the known thermal requirements of Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae) released in 1996, with those of an agent released in 1990, Niphograpta albiguttalis (Warren) (Lepidoptera: Pyralidae) and a candidate agent, Megamelus scutellaris Berg (Hemiptera: Delphacidae), which is currently under consideration for release. The lower developmental threshold (t_o) and rate of development (K) were determined for N. albiguttalis and M. scutellaris, using a reduced axis regression, and incorporated into a degree‐day model which compared the number of generations that E. catarinensis, N. albiguttalis, and M. scutellaris are capable of producing annually at any given site in South Africa. The degree‐day models predicted that N. albiguttalis (K = 439.43, t_o = 9.866) can complete 4–11 generations per year, whereas M. scutellaris (K =502.96, t_o = 11.458) can only complete 0–10 generations per year, compared with E. catarinensis (K = 342, t_o = 10.3) which is predicted to complete 3–14 generations per year. This suggests that the candidate agent, M. scutellaris, will not fare better in establishment than the other two agents that have been released in the Highveld, and that it may not be worth releasing an agent with higher thermal requirements than the agents that already occur in these high‐lying areas. Thermal physiology studies conducted prior to release are important tools in biological control programmes, particularly those in resource‐limited countries, to prevent wasting efforts in getting an agent established.     

Kin discrimination and outer membrane exchange in Myxococcus xanthus: A comparative analysis among natural isolates

Genetically similar cells of the soil bacterium Myxococcus xanthus cooperate at multiple social behaviours, including motility and multicellular development. Another social interaction in this species is outer membrane exchange (OME), a behaviour of unknown primary benefit in which cells displaying closely related variants of the outer membrane protein TraA transiently fuse and exchange membrane contents. Functionally incompatible TraA variants do not mediate OME, which led to the proposal that TraA incompatibilities determine patterns of intercellular cooperation in nature, but how this might occur remains unclear. Using natural isolates from a centimetre‐scale patch of soil, we analyse patterns of TraA diversity and ask whether relatedness at TraA is causally related to patterns of kin discrimination in the form of both colony‐merger incompatibilities (CMIs) and interstrain antagonisms. A large proportion of TraA functional diversity documented among global isolates is predicted to be contained within this cm‐scale population. We find evidence of balancing selection on the highly variable PA14‐portion of TraA and extensive transfer of traA alleles across genomic backgrounds. CMIs are shown to be common among strains identical at TraA, suggesting that CMIs are not generally caused by TraA dissimilarity. Finally, it has been proposed that interstrain antagonisms might be caused by OME‐mediated toxin transfer. However, we predict that most strain pairs previously shown to exhibit strong antagonisms are incapable of OME due to TraA dissimilarity. Overall, our results suggest that most documented patterns of kin discrimination in a natural population of M. xanthus are not causally related to the TraA sequences of interactants.     

Electrostatic potentials of the S‐locus F‐box proteins contribute to the pollen S specificity in self‐incompatibility in Petunia hybrida

Self‐incompatibility (SI) is a self/non‐self discrimination system found widely in angiosperms and, in many species, is controlled by a single polymorphic S‐locus. In the Solanaceae, Rosaceae and Plantaginaceae, the S‐locus encodes a single S‐RNase and a cluster of S‐locus F‐box (SLF) proteins to control the pistil and pollen expression of SI, respectively. Previous studies have shown that their cytosolic interactions determine their recognition specificity, but the physical force between their interactions remains unclear. In this study, we show that the electrostatic potentials of SLF contribute to the pollen S specificity through a physical mechanism of ‘like charges repel and unlike charges attract’ between SLFs and S‐RNases in Petunia hybrida. Strikingly, the alteration of a single C‐terminal amino acid of SLF reversed its surface electrostatic potentials and subsequently the pollen S specificity. Collectively, our results reveal that the electrostatic potentials act as a major physical force between cytosolic SLFs and S‐RNases, providing a mechanistic insight into the self/non‐self discrimination between cytosolic proteins in angiosperms.     

Self‐incompatibility and post‐fertilization maternal regulation cause low fecundity in Aegle marmelos (Rutaceae)

Outbreeding confers an evolutionary advantage, and flowering plants have evolved a variety of contrivances for its maximization. However, neither fruit set nor seed set is realized to its fullest potential for a variety of reasons. The causes of low flower to fruit and seed to ovule ratios were investigated in naturally occurring bael trees (Aegle marmelos) at two sites for three seasons. The study established that the mass effect of synchronized flowering attracted a variety of insect pollinators to the generalist flowers; Apis dorsata was the most efficient pollinator. The seed to ovule ratio was low despite high natural pollination efficiency (c. 2400 pollen per stigma). Although pollination‐induced structural and histochemical changes in the style allowed many (9.5 ± 2.1) pollen tubes to grow, only cross‐pollen tubes could grow through the style. Gametophytic self‐incompatibility, manifested in the stylar zone, resulted in a significantly slower growth rate of self‐pollen tubes. The occurrence of obligate self‐incompatibility, coupled with increased self‐pollen deposition (geitonogamy), caused a significant number of flowers to abort. Fruit retention in the trees declined from 40% to 12% as a result of abortion of fruits at different stages of development. The number of mature fruits on a tree was negatively correlated (r = ?0.82) with their size. It is inferred that low natural fecundity in A. marmelos is primarily a result of obligate self‐incompatibility and strong post‐fertilization maternal regulation of allocation of resources to the developing fruits. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 572–585.     

水稻雄性不育系珍汕97A小孢子发育过程中的微管骨架

水稻（Oryza sativaL.)雄性不育系珍汕97A,保持系珍汕97B和恢复系测64三系小孢子发生过程的研究表明;恢复系测64小孢子母细胞细胞质浓,有明显的微管荧光围绕着细胞核。小孢子母细胞经两次减数分裂形成四分体。四分体和小孢子的微管从细胞核表面向胞质周缘延伸,形成放射性排列格局,花粉发育正常。细胞质中有少量点状微管荧光,保持系珍汕97B小孢子发生过程的细胞形态和微管结构与恢复系测64相似。但细胞质中的点状微管荧光多一些。雄性不育系珍汕97A小孢子发生早期,小孢子母细胞内出现液泡,核中染色质凝集,微管荧光很弱,没有清晰的微管丝结构。细胞质中有许多点状微管荧光等不正常现象。小孢子母细胞经过减数分裂形成的四分体也没有清晰的丝状微管结构。随后,所有的小孢子迅速败育,雄性不育系珍汕97A在小孢子母细胞发生的很早时期,微管结构就明显不正常。