One of the widest ranging abiotic stresses in world agriculture arises from low iron (Fe) availability due to high soil pH, with 30% of arable land too alkaline for optimal crop production. To aquire Fe, Graminaceous plants use a chelation strategy and release phytosiderophores from their roots to chelate Fe (III) in the soil. Non-graminaceous plants differ from graminaceous plants in acquiring Fe, ferric reduction on root surface being the first step of iron uptake. Rice is very susceptible to low Fe availability. We enhanced the tolerance of rice to Fe deficiency in calcareous soils by introducing the barley genes participating in the phytosiderophore synthesis and tested these transgenic rice lines in a field experiment on a calcareous soil under paddy conditions. We showed that introducing barley genes involved in the synthesis of phytosiderophore into rice is an effective, practical method to improve agricultural productivity in calcareous soils. We also improved the tolerance of rice to Fe deficiency by increasing the ferric reductase activity of root cells by introducing the engineered gene refre1-372. To understand the molecular mechanisms that regulate Fe acquisition in plants, we analyzed the promoter region of the barley Fe deficiency inducible IDS2 gene and identified two novel cis-acting elements, IDE1 and IDE2. We identified two rice transcription factors, IDEF1 and IDEF2, which specifically bind to IDE1 and IDE2, respectively. The enhanced expression of transcription factors resulted in increased phytosiderophore secretion and tolerance to low Fe availability in a calcareous soil.
To remediate the worldwide-spreading acid sulphate soil area and utilize it for human beings, acid tolerant leguminous plants are expected to be useful as crops and pioneer plants. The purpose of this study is to produce symbiotic nitrogen fixing systems tolerant to acid sulfate soils, through the identification of the genes that confer acid tolerance on plants and the isolation of acid-tolerant rhizobia. We identified acid tolerant genes by two approaches. One approach is functional screening of a soybean cDNA library and their characterization in planta. E. coli cells were transformed with a cDNA library of soybean and cultured on a LB medium adjusted to pH 4 or pH 5. Selected six tolerant clones were introduced into Arabidopsis thaliana using a plant expression vector. The overexpressors grew better than the wild type under the acid and aluminium stresses. The other one is molecular genetic analysis of the candidate genes identified by previous studies: a gene for a key enzyme of sulfur assimilation, cysteine synthase. The candidate gene was ectopically overexpressed in A. thaliana under the control of the cauliflower mosaic virus 35S promoter. All the genes tested were shown to confer acid tolerance on the model plants.
I report the successful culture of the tardigrade Ramazzottius varieornatus by supplying the green alga Chlorella vulgaris as a food. A standard strain named YOKOZUNA-1 has been isolated from single egg of R. varieornatus. The reared animals have anhydrobiotic ability throughout their life cycle in eggs, juveniles, and adults. Body water content of adult R. varieornatus drops from 78.6% wt./wt. in hydrated state to 2.5% wt./wt. in anhydrobiotic state. Reared adults, while in an anhydrobiotic state, are tolerant of exposure to 100°C, 1 GPa, 99.8% acetonitrile, and 5000 Gy of 4He ions. Furthermore, hydrated active adults survive freezing at -2 to -20°C at a cooling rate of 1°C/min. Based on useful culture systems and extraordinary tolerance to extreme environmental conditions of R. varieornatus, this species is expected to be a suitable model for extremophile research focusing on multicellular organisms.
Dense animal communities at hydrothermal vents and cold seeps rely on symbioses with chemoautotrophic bacteria. To reveal the symbiotic mechanism, we sequenced the genome of chemoautotrophic intracellular symbiont in deep-sea clam, Calyptogena okutanii. On the other hand, C. magnifica symbiont genome sequenced in USA. The genomes appear to have been reduced. To understand their reductive genome evolution (RGE), we compared their genomes. They have small genomes containing chemoautotrophic and intracellular symbiotic features, and lack most genes for DNA recombination and repair e.g. recA and mutY. Their genome structures were highly conserved excepting one inversion. Many deletions from small (<100 bp) to large (>1 kbp up to 11 kbp) sizes were detected and deletion numbers decreased exponentially with size. Densities of deletions, short-repeat density and A+T content were higher in non-coding regions than in coding regions. Because Calyptogena symbiont genomes lack recA, we deduced that deletions and the inversion occurred by RecA-independent recombination (RIR) at short-repeats with simultaneous consumption of repeats, and that short-repeats were regenerated by high rate of mutation with enhanced A+T bias in the absence of mutY. We proposed that an active RGE is ongoing by short-repeats dependent RIR with regeneration of short-repeats in extant Calyptogena symbionts.
The growing body of research reveal that the programmed cell death (PCD) is ubiquitously distributed in microorganisms, plays key roles in developmental processes and inkeeping the integrity of bacterial communities. Inspired by this, bioengineers are making their original version of PCD devices for the temporal and/or spatial control of the bacteria communities. In this review, we discuss how PCD system should be designed and/or implemented into the bacteria to make a faithful and long-lasting &39;robots&39; for the real-world applications.