Changes in plasma membrane aquaporin gene expression under osmotic stress and blue light in tomato

Divergent abiotic stresses induce osmotic stress on plant cells resulting in an imbalance in water homeostasis which is preserved by aquaporins. Since the plasma membrane aquaporins (PIPs) were shown to be involved in seed development and responses to abiotic stresses, we focused on determining the contribution of mannitol-induced osmotic stress, blue light (BL), and 7B-1 mutation to their gene expression in tomato (Solanum lycopersicum L.) seeds. To assess that, we used a quantitative RT-PCR to determine the expression profiles of genes encoding PIPs. Subsequently, a multiple linear regression analysis was used to evaluate the impact of studied stressors (mannitol and BL) and 7B-1 mutation on PIP gene expressions. We found that mannitol-induced osmotic stress and 7B-1 mutation (conferring the lower responsiveness to osmotic stress- and BL-induced inhibition of seed germination) decreased expression of PIP1;3, PIP2;3 and PIP1;2, PIP2;1 genes, respectively. This might be a way to retain water for radicle elongation and seed germination under the stress conditions. Interestingly, the expression of PIP1;3 gene was downregulated not only by osmotic stress, but also by BL. Altogether, our data indicate the existence of a link between osmotic stress and BL signalling and the involvement of the 7B-1 mutation in this crosstalk.     

Aquaporin expression during seed osmopriming and post-priming germination in spinach

Aquaporins (AQPs) are proteinaceous channels known to regulate transmembrane water transport, and therefore may be important component of imbibition during osmopriming and germination. To explore the association between AQPs and osmopriming-led enhanced germination performance, we studied the expression patterns of four spinach (Spinacia oleracea) AQP coding genes (SoPIP1;1, SoPIP1;2, SoPIP2;1, and SoδTIP) during osmopriming and subsequent germination under optimal conditions, chilling and drought. All these genes were up-regulated within 2–4 d of priming (phase II-imbibition). We hypothesize such up-regulation to facilitate the pressure potential-driven cell expansion and increase germination potential of primed seeds. Our data during post-priming germination suggest that SoPIP1;1 and SoδTIP were more closely associated with enhanced germination performance. In general, all AQPs were downregulated under chilling and drought. However, under chilling, SoPIP2;1 was expressed at relatively higher level in primed seeds that also exhibited greater chilling tolerance, while SoPIP1;2 and SoδTIP exhibited opposite pattern. Similarly, SoPIP1;1, SoPIP2;1, and SoδTIP exhibited higher expression in primed seeds that also had greater drought tolerance.     

Molecular genetics and functional genomics of abiotic stress-responsive genes in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.): a review of recent advances and future

Abiotic stresses are the key factors which negatively influence plant development and productivity and are the main cause of extensive agricultural production losses worldwide. Brassica napus is an oilseed crop of global economic significance and major contributor to the total oilseed production, quite often encounters abiotic stresses, resulting in reduced agricultural productivity. Hence, there is an immediate need being felt to raise B. napus cultivars which would be more suitable for various abiotic stress conditions presently and in the years to come. Biotechnology and molecular plant breeding has emerged as an important tool for molecular understanding of plant response to various abiotic stresses. Currently, various stress-responsive genes and mechanisms have been identified and functionally characterized in model plant Arabidopsis and other major crop plants such as Oryza sativa and Zea mays. However, very inadequate success has been achieved in this direction in a major oilseed crop such as B. napus. In this review, we present the latest methods and approaches of studying abiotic stress in B. napus. In this review, we describe the genes functioning as markers for crop breeding and discuss the recent progress and advances in genome editing by break through CRISPR/Cas9 multigene–multiplex approaches for developing multiple abiotic stress tolerance with our on-going research as a scheme. We also throw some light on molecular genetics, plant breeding and abiotic stress biotechnology of B. napus which offer a new prospective on the research directions for the practical plant breeding and functional genomics of B. napus in response to different abiotic stress conditions.     

Heterologous Expression of Two Jatropha Aquaporins Imparts Drought and Salt Tolerance and Improves Seed Viability in Transgenic Arabidopsis thaliana

Drought and high salinity are environmental conditions that cause adverse effects on the growth and productivity of crops. Aquaporins are small integral membrane proteins that belong to the family of the major intrinsic proteins (MIPs), with members in animals, plants and microbes, where they facilitate the transport of water and/or small neutral solutes thereby affecting water balance. In this study we characterized two aquaporin genes namely, plasma membrane intrinsic protein (PIP2;7) and tonoplast intrinsic protein TIP1;3 from Jatropha curcas that are localised to the plasma membrane and vacuole respectively. Transgenic Arabidopsis thaliana lines over-expressing JcPIP2;7 and JcTIP1;3 under a constitutive promoter show improved germination under high salt and mannitol compared to control seeds. These transgenic plants also show increased root length under abiotic stress conditions compared to wild type Col-0 plants. Transgenic lines exposed to drought conditions by withholding water for 20 days, were able to withstand water stress and attained normal growth after re-watering unlike control plants which could not survive. Transgenic lines also had better seed yield than control under salt stress. Importantly, seed viability of transgenic plants grown under high salt concentration was 35%-45% compared to less than 5% for control seeds obtained from plants growing under salt stress. The effect of JcPIP2;7 and JcTIP1;3 on improving germination and seed viability in drought and salinity make these important candidates for genetic manipulation of plants for growth in saline soils.     

Transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis> and tobacco plants overexpressing an aquaporin respond differently to various abiotic stresses

Despite the high isoform multiplicity of aquaporins in plants, with 35 homologues including 13 plasma membrane intrinsic proteins (PIPs) in Arabidosis thaliana, the individual and integrated functions of aquaporins under various physiological conditions remain unclear. To better understand aquaporin functions in plants under various stress conditions, we examined transgenic Arabidopsis and tobacco plants that constitutively overexpress Arabidopsis PIP1;4 or PIP2;5 under various abiotic stress conditions. No significant differences in growth rates and water transport were found between the transgenic and wild-type plants when grown under favorable growth conditions. The transgenic plants overexpressing PIP1;4 or PIP2;5 displayed a rapid water loss under dehydration stress, which resulted in retarded germination and seedling growth under drought stress. In contrast, the transgenic plants overexpressing PIP1;4 or PIP2;5 showed enhanced water flow and facilitated germination under cold stress. The expression of several PIPs was noticeably affected by the overexpression of PIP1;4 or PIP2;5 in Arabidopsis under dehydration stress, suggesting that the expression of one aquaporin isoform influences the expression levels of other aquaporins under stress conditions. Taken together, our results demonstrate that overexpression of an aquaporin affects the expression of endogenous aquaporin genes and thereby impacts on seed germination, seedling growth, and stress responses of the plants under various stress conditions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Water transport by aquaporins in the extant plant Physcomitrella patens

Although aquaporins (AQPs) have been shown to increase membrane water permeability in many cell types, the physiological role of this increase was not always obvious. In this report, we provide evidence that in the leafy stage of development (gametophore) of the moss Physcomitrella patens, AQPs help to replenish more rapidly the cell water that is lost by transpiration, at least if some water is in the direct vicinity of the moss plant. Three AQP genes were cloned in P. patens: PIP2;1, PIP2;2, and PIP2;3. The water permeability of the membrane was measured in protoplasts from leaves and protonema. A significant decrease was measured in protoplasts from leaves and protonema of PIP2;1 or PIP2;2 knockouts but not the PIP2;3 knockout. No phenotype was observed when knockout plants were grown in closed petri dishes with ample water supply. Gametophores isolated from the wild type and the pip2;3 mutant were not sensitive to moderate water stress, but pip2;1 or pip2;2 gametophores expressed a water stress phenotype. The knockout mutant leaves were more bent and twisted, apparently suffering from an important loss of cellular water. We propose a model to explain how the AQPs PIP2;1 and PIP2;2 delay leaf dessication in a drying atmosphere. We suggest that in ancestral land plants, some 400 million years ago, APQs were already used to facilitate the absorption of water.     

Cloning of Ten Peroxidase (<Emphasis Type="Italic">POD</Emphasis>) Genes from <Emphasis Type="Italic">Tamarix Hispida</Emphasis> and Characterization of their Responses to Abiotic Stress

Plant peroxidases (PODs) have been ascribed a variety of biological functions, including hydrogen peroxide detoxification, lignin biosynthesis, hormonal signaling, and stress response. In the present study, ten POD genes, including three ascorbate peroxidases (class I PODs) and seven secretory peroxidases (class III PODs), were cloned from Tamarix hispida. The roles of the ten POD genes were addressed under different abiotic stress conditions, and gene expression profiles in roots, stems, and leaves were evaluated using real-time quantitative reverse-transcribed polymerase chain reaction. Our results showed that the relative abundance of the PODs was markedly different in roots, stems, and leaves, indicating that POD activity differs in these three organs. ThPOD1 and ThPOD8 were the most and least abundant, respectively, in all organs. The expression profiles in response to abiotic stresses were organ specific. All of the genes were highly induced by drought, salt, salt–alkaline, CdCl₂, and abscisic acid (ABA) treatments in at least one organ. Five ThPOD genes were induced in roots, stems, and leaves under all of the studied stress conditions, indicating that they are closely associated with abiotic stress. Our results demonstrate that the ten plant peroxidases are all expressed in leaves, stems, and roots, that they are involved in different abiotic stress responses, and that they are controlled by an ABA-dependent stress signaling pathway.