Two cytosolic glutamine synthetase isoforms play specific roles for seed germination and seed yield structure in <i>Arabidopsis</i>

Nitrogen (N) remobilization from reserves to sinks is essential for seedling establishment and seed production. Cytosolic glutamine synthetase (GS1) is up-regulated during both seed germination and seed filling in plants. However, the specific roles of the individual GS1 isogenes with respect to N remobilization, early seedling vigour, and final seed productivity are not known. In this study, impairment of seed germination and seedling establishment is demonstrated in the single knockout mutant gln1;2, and the double knockout mutant gln1;1:gln1;2. The negative effect of Gln1;2 deficiency was associated with reduced N remobilization from the cotyledons and could be fully alleviated by exogenous N supply. Following reproductive growth, both the single and double Gln1;2-knockout mutants showed decreased seed yield due to fewer siliques, less seeds per silique, and lower dry weight per seed. The gln1;1 single mutant had normal seed yield structure but primary root development during seed germination was reduced in the presence of external N. Gln1;2 promoter–green fluorescent protein constructs showed that Gln1;2 localizes to the vascular cells of roots, petals, and stamens. It is concluded that Gln1;2 plays an important role in N remobilization for both seedling establishment and seed production in Arabidopsis

Improved Salinity Tolerance of Rice Through Cell Type-Specific Expression of AtHKT1;1

Previously, cell type-specific expression of AtHKT1;1, a sodium transporter, improved sodium (Na+) exclusion and salinity tolerance in Arabidopsis. In the current work, AtHKT1;1, was expressed specifically in the root cortical and epidermal cells of an Arabidopsis GAL4-GFP enhancer trap line. These transgenic plants were found to have significantly improved Na+ exclusion under conditions of salinity stress. The feasibility of a similar biotechnological approach in crop plants was explored using a GAL4-GFP enhancer trap rice line to drive expression of AtHKT1;1 specifically in the root cortex. Compared with the background GAL4-GFP line, the rice plants expressing AtHKT1;1 had a higher fresh weight under salinity stress, which was related to a lower concentration of Na+ in the shoots. The root-to-shoot transport of 22Na+ was also decreased and was correlated with an upregulation of OsHKT1;5, the native transporter responsible for Na+ retrieval from the transpiration stream. Interestingly, in the transgenic Arabidopsis plants overexpressing AtHKT1;1 in the cortex and epidermis, the native AtHKT1;1 gene responsible for Na+ retrieval from the transpiration stream, was also upregulated. Extra Na+ retrieved from the xylem was stored in the outer root cells and was correlated with a significant increase in expression of the vacuolar pyrophosphatases (in Arabidopsis and rice) the activity of which would be necessary to move the additional stored Na+ into the vacuoles of these cells. This work presents an important step in the development of abiotic stress tolerance in crop plants via targeted changes in mineral transport

Na⁺transport in glycophytic plants:what we know and would like to know

Soil salinity decreases the growth rate of plants and can severely limit the productivity of crop plants. The ability to tolerate salinity stress differs widely between species of plants as well as within species. As an important component of salinity tolerance, a better understanding of the mechanisms of Na(+) transport will assist in the development of plants with improved salinity tolerance and, importantly, might lead to increased yields from crop plants growing in challenging environments. This review summarizes the current understanding of the components of Na(+) transport in glycophytic plants, including those at the soil to root interface, transport of Na(+) to the xylem, control of Na(+) loading in the stele and partitioning of the accumulated Na(+) within the shoot and individual cells. Using this knowledge, strategies to modify Na(+) transport and engineer plant salinity tolerance, as well as areas of research which merit particular attention in order to further improve the understanding of salinity tolerance in plants, are discussed.Darren Craig Plett & Inge Skrumsager Mølle

Improving nitrogen use efficiency in barley (Hordeum vulgare L.) through the cisgenic approach

Barley is one of the major crops cultivated worldwide and constitutes an important basis for animal feed. However, the production is facing a number of challenges that will be accentuated in the years to come, in particular restrictions on the use of nitrogen (N) fertilizer. In order to improve the N use efficiency in barley, we are developing a new generation of genetically modified plants based on the concept of cisgenesis. In this approach, plants are transformed only with their own genetic material. The genes encoding the cytosolic isoform of the glutamine synthetase (GS1) and the tonoplast intrinsic protein TIP2, potentially involve in N management and plant growth, have been selected to be transformed into the barley cultivar Golden Promise. The genomic clones comprising 1-2kb of the promoter, the gene itself and 0.5-1kb of the 3’untranslated region have been isolated and cloned into the pGreenII binary vector. The genes have been inserted into barley by Agrobacterium-mediated transformation using the hygromycin phosphotransferase gene for selection of transformed lines on hygromycin. In this system, the resistance gene is placed on the helper plasmid pSoup allowing for separate introductions of the gene of interest and the resistance gene for selection, respectively.The transgenic lines (T0), currently growing in greenhouse will be self pollinated and the molecular, physiological and agronomic characterization of subsequent generations will be undertaken