Golden bananas in the field: elevated fruit pro‐vitamin A from the expression of a single banana transgene

Vitamin A deficiency remains one of the world's major public health problems despite food fortification and supplements strategies. Biofortification of staple crops with enhanced levels of pro‐vitamin A (PVA) offers a sustainable alternative strategy to both food fortification and supplementation. As a proof of concept, PVA‐biofortified transgenic Cavendish bananas were generated and field trialed in Australia with the aim of achieving a target level of 20 μg/g of dry weight (dw) β‐carotene equivalent (β‐CE) in the fruit. Expression of a Fe'i banana‐derived phytoene synthase 2a (MtPsy2a) gene resulted in the generation of lines with PVA levels exceeding the target level with one line reaching 55 μg/g dw β‐CE . Expression of the maize phytoene synthase 1 (ZmPsy1) gene, used to develop ‘Golden Rice 2’, also resulted in increased fruit PVA levels although many lines displayed undesirable phenotypes. Constitutive expression of either transgene with the maize polyubiquitin promoter increased PVA accumulation from the earliest stage of fruit development. In contrast, PVA accumulation was restricted to the late stages of fruit development when either the banana 1‐aminocyclopropane‐1‐carboxylate oxidase or the expansin 1 promoters were used to drive the same transgenes. Wild‐type plants with the longest fruit development time had also the highest fruit PVA concentrations. The results from this study suggest that early activation of the rate‐limiting enzyme in the carotenoid biosynthetic pathway and extended fruit maturation time are essential factors to achieve optimal PVA concentrations in banana fruit.     

Physiological and molecular mechanisms underlying the integration of light and temperature cues in Arabidopsis thaliana seeds

The relief of dormancy and the promotion of seed germination are of extreme importance for a successful seedling establishment. Although alternating temperatures and light are signals promoting the relief of seed dormancy, the underlying mechanisms of their interaction in seeds are scarcely known. By exposing imbibed Arabidopsis thaliana dormant seeds to two‐day temperature cycles previous of a red light pulse, we demonstrate that the germination mediated by phytochrome B requires the presence of functional PSEUDO‐RESPONSE REGULATOR 7 (PRR7) and TIMING OF CAB EXPRESSION 1 (TOC1) alleles. In addition, daily cycles of alternating temperatures in darkness reduce the protein levels of DELAY OF GERMINATION 1 (DOG1), allowing the expression of TOC1 to induce seed germination. Our results suggest a functional role for some components of the circadian clock related with the action of DOG1 for the integration of alternating temperatures and light signals in the relief of seed dormancy. The synchronization of germination by the synergic action of light and temperature through the activity of circadian clock might have ecological and adaptive consequences.     

Range expansion and ancestral niche reconstruction in the Mediterranean diving beetle genus Meladema (Coleoptera,Dytiscidae)

Species of the genus Meladema (Dytiscidae, Colymbetinae) are some of the largest macroinvertebrates in the western Palearctic region, being top predators in fishless streams. Two of the three described species, Meladema imbricata (Wollaston, 1871) and Meladema lanio (Fabricius, 1775) are Macaronesian endemics from the Canary Islands and Madeira, respectively, while the third, Meladema coriacea Laporte, 1835, is widely distributed from Morocco and the Iberian Peninsula to Turkey, including the Canary Islands. Previous phylogenetic analysis using only mitochondrial markers revealed the existence of two cryptic lineages within M. coriacea, one restricted to Corsica and the other including the rest of sampled populations. We reconstruct here the evolutionary history of the species of Meladema using a more comprehensive sampling covering its whole geographical range, adding nuclear markers and Bayesian molecular dating. Using environmental niche modelling, we test for possible differences in climatic preferences among lineages and reconstruct their ancestral climatic niche. Our results strongly supported the existence of four monophyletic lineages represented by the three recognized species plus a fourth cryptic lineage with populations of M. coriacea from the Tyrrhenian islands (Corsica, Sardinia and Montecristo). This pattern is not likely to be the result of mitochondrial artefacts due to Wolbachia infection, as all 11 tested individuals were negative for this parasite. Dating analysis placed the origin of Meladema in the Middle Miocene although diversification among extant Meladema lineages started in the early Pleistocene and took place in a relatively short time period. Phylogeographic analysis inferred a continental origin of Meladema, with an independent colonization of the Macaronesian and Mediterranean islands. From the south‐western Mediterranean region, the continental M. coriacea expanded its range up to Bulgaria and Turkey in the northern basin and to Tunisia in the southern. Results of niche modelling showed that seasonality is the critical factor in shaping the current distribution of Meladema. Island lineages (M. imbricata, M. lanio and the Tyrrhenian lineage of M. coriacea) occur in sites with low seasonality, within the range of the reconstructed ancestral climatic niche of the genus. On the contrary, continental M. coriacea expanded its range to localities outside the ancestral climatic range of the genus, with a higher seasonality and aridity.     

Phosphorylation of Pkp1 by RIPK4 regulates epidermal differentiation and skin tumorigenesis

Tissue homeostasis of skin is sustained by epidermal progenitor cells localized within the basal layer of the skin epithelium. Post‐translational modification of the proteome, such as protein phosphorylation, plays a fundamental role in the regulation of stemness and differentiation of somatic stem cells. However, it remains unclear how phosphoproteomic changes occur and contribute to epidermal differentiation. In this study, we survey the epidermal cell differentiation in a systematic manner by combining quantitative phosphoproteomics with mammalian kinome cDNA library screen. This approach identified a key signaling event, phosphorylation of a desmosome component, PKP1 (plakophilin‐1) by RIPK4 (receptor‐interacting serine–threonine kinase 4) during epidermal differentiation. With genome‐editing and mouse genetics approach, we show that loss of function of either Pkp1 or Ripk4 impairs skin differentiation and enhances epidermal carcinogenesis in vivo. Phosphorylation of PKP1's N‐terminal domain by RIPK4 is essential for their role in epidermal differentiation. Taken together, our study presents a global view of phosphoproteomic changes that occur during epidermal differentiation, and identifies RIPK‐PKP1 signaling as novel axis involved in skin stratification and tumorigenesis.     

Histone H4K20 tri‐methylation at late‐firing origins ensures timely heterochromatin replication

Among other targets, the protein lysine methyltransferase PR‐Set7 induces histone H4 lysine 20 monomethylation (H4K20me1), which is the substrate for further methylation by the Suv4‐20h methyltransferase. Although these enzymes have been implicated in control of replication origins, the specific contribution of H4K20 methylation to DNA replication remains unclear. Here, we show that H4K20 mutation in mammalian cells, unlike in Drosophila, partially impairs S‐phase progression and protects from DNA re‐replication induced by stabilization of PR‐Set7. Using Epstein–Barr virus‐derived episomes, we further demonstrate that conversion of H4K20me1 to higher H4K20me2/3 states by Suv4‐20h is not sufficient to define an efficient origin per se, but rather serves as an enhancer for MCM2‐7 helicase loading and replication activation at defined origins. Consistent with this, we find that Suv4‐20h‐mediated H4K20 tri‐methylation (H4K20me3) is required to sustain the licensing and activity of a subset of ORCA/LRWD1‐associated origins, which ensure proper replication timing of late‐replicating heterochromatin domains. Altogether, these results reveal Suv4‐20h‐mediated H4K20 tri‐methylation as a critical determinant in the selection of active replication initiation sites in heterochromatin regions of mammalian genomes.     

Structure of a Pancreatic ATP-Sensitive Potassium Channel

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药物外排泵与生物被膜在微生物耐药机制中的相关性研究进展

生物被膜是介导微生物耐药与多重耐药的一大热点机制,涉及微生物的生长代谢、耐药基因等基因表型改变、群体感应系统的调控及药物外排泵等多重因素。耐药基因、药物外排泵与生物被膜在微生物耐药机制中,具有复杂而密切的相互影响。分别从生物被膜对药物外排泵、耐药基因的影响,药物外排泵对生物被膜的影响,以及药物外排泵和微生物生物被膜共同的调节因素,对近年来的相关研究进展作一综述。