Potential abiotic stress targets for modern genetic manipulation.

Research into crop yield and resilience has underpinned global food security, evident in yields tripling in the past 5 decades. The challenges that global agriculture now faces are not just to feed 10+ billion people within a generation, but to do so under a harsher, more variable, and less predictable climate, and in many cases with less water, more expensive inputs, and declining soil quality. The challenges of climate change are not simply to breed for a "hotter drier climate," but to enable resilience to floods and droughts and frosts and heat waves, possibly even within a single growing season. How well we prepare for the coming decades of climate variability will depend on our ability to modify current practices, innovate with novel breeding methods, and communicate and work with farming communities to ensure viability and profitability. Here we define how future climates will impact farming systems and growing seasons, thereby identifying the traits and practices needed and including exemplars being implemented and developed. Critically, this review will also consider societal perspectives and public engagement about emerging technologies for climate resilience, with participatory approaches presented as the best approach.

Osmotic adjustment and energy limitations to plant growth in saline soil.

Plant roots must exclude almost all of the Na+ and Cl- in saline soil while taking up water, otherwise these ions would build up to high concentrations in leaves. Plants evaporate c. 50 times more water than they retain, so 98% exclusion would result in shoot NaCl concentrations equal to that of the external medium. Taking up just 2% of the NaCl allows a plant to osmotically adjust the Na+ and Cl- in vacuoles, while organic solutes provide the balancing osmotic pressure in the cytoplasm. We quantify the costs of this exclusion by roots, the regulation of Na+ and Cl- transport through the plant, and the costs of osmotic adjustment with organic solutes in roots.

Energy costs of salt tolerance in crop plants.

Agriculture is expanding into regions that are affected by salinity. This review considers the energetic costs of salinity tolerance in crop plants and provides a framework for a quantitative assessment of costs. Different sources of energy, and modifications of root system architecture that would maximize water vs ion uptake are addressed. Energy requirements for transport of salt (NaCl) to leaf vacuoles for osmotic adjustment could be small if there are no substantial leaks back across plasma membrane and tonoplast in root and leaf. The coupling ratio of the H+ -ATPase also is a critical component. One proposed leak, that of Na+ influx across the plasma membrane through certain aquaporin channels, might be coupled to water flow, thus conserving energy. For the tonoplast, control of two types of cation channels is required for energy efficiency. Transporters controlling the Na+ and Cl- concentrations in mitochondria and chloroplasts are largely unknown and could be a major energy cost. The complexity of the system will require a sophisticated modelling approach to identify critical transporters, apoplastic barriers and root structures. This modelling approach will inform experimentation and allow a quantitative assessment of the energy costs of NaCl tolerance to guide breeding and engineering of molecular components.

Phosphorylation influences water and ion channel function of AtPIP2;1.

The phosphorylation state of two serine residues within the C-terminal domain of AtPIP2;1 (S280, S283) regulates its plasma membrane localization in response to salt and osmotic stress. Here, we investigated whether the phosphorylation state of S280 and S283 also influence AtPIP2;1 facilitated water and cation transport. A series of single and double S280 and S283 phosphomimic and phosphonull AtPIP2;1 mutants were tested in heterologous systems. In Xenopus laevis oocytes, phosphomimic mutants AtPIP2;1 S280D, S283D, and S280D/S283D had significantly greater ion conductance for Na+ and K+ , whereas the S280A single phosphonull mutant had greater water permeability. We observed a phosphorylation-dependent inverse relationship between AtPIP2;1 water and ion transport with a 10-fold change in both. The results revealed that phosphorylation of S280 and S283 influences the preferential facilitation of ion or water transport by AtPIP2;1. The results also hint that other regulatory sites play roles that are yet to be elucidated. Expression of the AtPIP2;1 phosphorylation mutants in Saccharomyces cerevisiae confirmed that phosphorylation influences plasma membrane localization, and revealed higher Na+ accumulation for S280A and S283D mutants. Collectively, the results show that phosphorylation in the C-terminal domain of AtPIP2;1 influences its subcellular localization and cation transport capacity.

Deciphering aquaporin regulation and roles in seed biology.

Seeds are the typical dispersal and propagation units of angiosperms and gymnosperms. Water movement into and out of seeds plays a crucial role from the point of fertilization through to imbibition and seed germination. A class of membrane intrinsic proteins called aquaporins (AQPs) assist with the movement of water and other solutes within seeds. These highly diverse and abundant proteins are associated with different processes in the development, longevity, imbibition, and germination of seed. However, there are many AQPs encoded in a plant's genome and it is not yet clear how, when, or which AQPs are involved in critical stages of seed biology. Here we review the literature to examine the evidence for AQP involvement in seeds and analyse Arabidopsis seed-related transcriptomic data to assess which AQPs are likely to be important in seed water relations and explore additional roles for AQPs in seed biology.

Overexpression of HvCslF6 in barley grain alters carbohydrate partitioning plus transfer tissue and endosperm development.

In cereal grain, sucrose is converted into storage carbohydrates: mainly starch, fructan, and mixed-linkage (1,3;1,4)-ß-glucan (MLG). Previously, endosperm-specific overexpression of the HvCslF6 gene in hull-less barley was shown to result in high MLG and low starch content in mature grains. Morphological changes included inwardly elongated aleurone cells, irregular cell shapes of peripheral endosperm, and smaller starch granules of starchy endosperm. Here we explored the physiological basis for these defects by investigating how changes in carbohydrate composition of developing grain impact mature grain morphology. Augmented MLG coincided with increased levels of soluble carbohydrates in the cavity and endosperm at the storage phase. Transcript levels of genes relating to cell wall, starch, sucrose, and fructan metabolism were perturbed in all tissues. The cell walls of endosperm transfer cells (ETCs) in transgenic grain were thinner and showed reduced mannan labelling relative to the wild type. At the early storage phase, ruptures of the non-uniformly developed ETCs and disorganization of adjacent endosperm cells were observed. Soluble sugars accumulated in the developing grain cavity, suggesting a disturbance of carbohydrate flow from the cavity towards the endosperm, resulting in a shrunken mature grain phenotype. Our findings demonstrate the importance of regulating carbohydrate partitioning in maintenance of grain cellularization and filling processes.

A Survey of Barley PIP Aquaporin Ionic Conductance Reveals Ca2+-Sensitive HvPIP2;8 Na+ and K+ Conductance.

Some plasma membrane intrinsic protein (PIP) aquaporins can facilitate ion transport. Here we report that one of the 12 barley PIPs (PIP1 and PIP2) tested, HvPIP2;8, facilitated cation transport when expressed in Xenopus laevis oocytes. HvPIP2;8-associated ion currents were detected with Na+ and K+, but not Cs+, Rb+, or Li+, and was inhibited by Ba2+, Ca2+, and Cd2+ and to a lesser extent Mg2+, which also interacted with Ca2+. Currents were reduced in the presence of K+, Cs+, Rb+, or Li+ relative to Na+ alone. Five HvPIP1 isoforms co-expressed with HvPIP2;8 inhibited the ion conductance relative to HvPIP2;8 alone but HvPIP1;3 and HvPIP1;4 with HvPIP2;8 maintained the ion conductance at a lower level. HvPIP2;8 water permeability was similar to that of a C-terminal phosphorylation mimic mutant HvPIP2;8 S285D, but HvPIP2;8 S285D showed a negative linear correlation between water permeability and ion conductance that was modified by a kinase inhibitor treatment. HvPIP2;8 transcript abundance increased in barley shoot tissues following salt treatments in a salt-tolerant cultivar Haruna-Nijo, but not in salt-sensitive I743. There is potential for HvPIP2;8 to be involved in barley salt-stress responses, and HvPIP2;8 could facilitate both water and Na+/K+ transport activity, depending on the phosphorylation status.

Roles of membrane transporters: connecting the dots from sequence to phenotype.

BACKGROUND: Plant membrane transporters are involved in diverse cellular processes underpinning plant physiology, such as nutrient acquisition, hormone movement, resource allocation, exclusion or sequestration of various solutes from cells and tissues, and environmental and developmental signalling. A comprehensive characterization of transporter function is therefore key to understanding and improving plant performance. SCOPE AND CONCLUSIONS: In this review, we focus on the complexities involved in characterizing transporter function and the impact that this has on current genomic annotations. Specific examples are provided that demonstrate why sequence homology alone cannot be relied upon to annotate and classify transporter function, and to show how even single amino acid residue variations can influence transporter activity and specificity. Misleading nomenclature of transporters is often a source of confusion in transporter characterization, especially for people new to or outside the field. Here, to aid researchers dealing with interpretation of large data sets that include transporter proteins, we provide examples of transporters that have been assigned names that misrepresent their cellular functions. Finally, we discuss the challenges in connecting transporter function at the molecular level with physiological data, and propose a solution through the creation of new databases. Further fundamental in-depth research on specific transport (and other) proteins is still required; without it, significant deficiencies in large-scale data sets and systems biology approaches will persist. Reliable characterization of transporter function requires integration of data at multiple levels, from amino acid residue sequence annotation to more in-depth biochemical, structural and physiological studies.

Structural variations in wheat HKT1;5 underpin differences in Na+ transport capacity.

An important trait associated with the salt tolerance of wheat is the exclusion of sodium ions (Na+) from the shoot. We have previously shown that the sodium transporters TmHKT1;5-A and TaHKT1;5-D, from Triticum monoccocum (Tm) and Triticum aestivum (Ta), are encoded by genes underlying the major shoot Na+-exclusion loci Nax1 and Kna1, respectively. Here, using heterologous expression, we show that the affinity (K m) for the Na+ transport of TmHKT1;5-A, at 2.66 mM, is higher than that of TaHKT1;5-D at 7.50 mM. Through 3D structural modelling, we identify residues D471/a gap and D474/G473 that contribute to this property. We identify four additional mutations in amino acid residues that inhibit the transport activity of TmHKT1;5-A, which are predicted to be the result of an occlusion of the pore. We propose that the underlying transport properties of TmHKT1;5-A and TaHKT1;5-D contribute to their unique ability to improve Na+ exclusion in wheat that leads to an improved salinity tolerance in the field.

The sodium transporter encoded by the HKT1;2 gene modulates sodium/potassium homeostasis in tomato shoots under salinity.

Excessive soil salinity diminishes crop yield and quality. In a previous study in tomato, we identified two closely linked genes encoding HKT1-like transporters, HKT1;1 and HKT1;2, as candidate genes for a major quantitative trait locus (kc7.1) related to shoot Na+ /K+ homeostasis - a major salt tolerance trait - using two populations of recombinant inbred lines (RILs). Here, we determine the effectiveness of these genes in conferring improved salt tolerance by using two near-isogenic lines (NILs) that were homozygous for either the Solanum lycopersicum allele (NIL17) or for the Solanum cheesmaniae allele (NIL14) at both HKT1 loci; transgenic lines derived from these NILs in which each HKT1;1 and HKT1;2 had been silenced by stable transformation were also used. Silencing of ScHKT1;2 and SlHKT1;2 altered the leaf Na+ /K+ ratio and caused hypersensitivity to salinity in plants cultivated under transpiring conditions, whereas silencing SlHKT1;1/ScHKT1;1 had a lesser effect. These results indicate that HKT1;2 has the more significant role in Na+ homeostasis and salinity tolerance in tomato.

Non-selective cation channel activity of aquaporin AtPIP2;1 regulated by Ca2+ and pH.

The aquaporin AtPIP2;1 is an abundant plasma membrane intrinsic protein in Arabidopsis thaliana that is implicated in stomatal closure, and is highly expressed in plasma membranes of root epidermal cells. When expressed in Xenopus laevis oocytes, AtPIP2;1 increased water permeability and induced a non-selective cation conductance mainly associated with Na+ . A mutation in the water pore, G103W, prevented both the ionic conductance and water permeability of PIP2;1. Co-expression of AtPIP2;1 with AtPIP1;2 increased water permeability but abolished the ionic conductance. AtPIP2;2 (93% identical to AtPIP2;1) similarly increased water permeability but not ionic conductance. The ionic conductance was inhibited by the application of extracellular Ca2+ and Cd2+ , with Ca2+ giving a biphasic dose-response with a prominent IC50 of 0.32 mм comparable with a previous report of Ca2+ sensitivity of a non-selective cation channel (NSCC) in Arabidopsis root protoplasts. Low external pH also inhibited ionic conductance (IC50 pH 6.8). Xenopus oocytes and Saccharomyces cerevisiae expressing AtPIP2;1 accumulated more Na+ than controls. Establishing whether AtPIP2;1 has dual ion and water permeability in planta will be important in understanding the roles of this aquaporin and if AtPIP2;1 is a candidate for a previously reported NSCC responsible for Ca2+ and pH sensitive Na+ entry into roots.

Divalent Cations Regulate the Ion Conductance Properties of Diverse Classes of Aquaporins.

Aquaporins (AQPs) are known to facilitate water and solute fluxes across barrier membranes. An increasing number of AQPs are being found to serve as ion channels. Ion and water permeability of selected plant and animal AQPs (plant Arabidopsis thaliana AtPIP2;1, AtPIP2;2, AtPIP2;7, human Homo sapiens HsAQP1, rat Rattus norvegicus RnAQP4, RnAQP5, and fly Drosophilamelanogaster DmBIB) were expressed in Xenopus oocytes and examined in chelator-buffered salines to evaluate the effects of divalent cations (Ca2+, Mg2+, Ba2+ and Cd2+) on ionic conductances. AtPIP2;1, AtPIP2;2, HsAQP1 and DmBIB expressing oocytes had ionic conductances, and showed differential sensitivity to block by external Ca2+. The order of potency of inhibition by Ca2+ was AtPIP2;2 > AtPIP2;1 > DmBIB > HsAQP1. Blockage of the AQP cation channels by Ba2+ and Cd2+ caused voltage-sensitive outward rectification. The channels with the highest sensitivity to Ca2+ (AtPIP2;1 and AtPIP2;2) showed a distinctive relief of the Ca2+ block by co-application of excess Ba2+, suggesting that divalent ions act at the same site. Recognizing the regulatory role of divalent cations may enable the discovery of other classes of AQP ion channels, and facilitate the development of tools for modulating AQP ion channels. Modulators of AQPs have potential value for diverse applications including improving salinity tolerance in plants, controlling vector-borne diseases, and intervening in serious clinical conditions involving AQPs, such as cancer metastasis, cardiovascular or renal dysfunction.

Genetics and physiology of cell wall polysaccharides in the model C4 grass, Setaria viridis spp.

BACKGROUND: Setaria viridis has emerged as a model species for the larger C4 grasses. Here the cellulose synthase (CesA) superfamily has been defined, with an emphasis on the amounts and distribution of (1,3;1,4)-ß-glucan, a cell wall polysaccharide that is characteristic of the grasses and is of considerable value for human health. METHODS: Orthologous relationship of the CesA and Poales-specific cellulose synthase-like (Csl) genes among Setaria italica (Si), Sorghum bicolor (Sb), Oryza sativa (Os), Brachypodium distachyon (Bradi) and Hordeum vulgare (Hv) were compared using bioinformatics analysis. Transcription profiling of Csl gene families, which are involved in (1,3;1,4)-ß-glucan synthesis, was performed using real-time quantitative PCR (Q-PCR). The amount of (1,3;1,4)-ß-glucan was measured using a modified Megazyme assay. The fine structures of the (1,3;1,4)-ß-glucan, as denoted by the ratio of cellotriosyl to cellotetraosyl residues (DP3:DP4 ratio) was assessed by chromatography (HPLC and HPAEC-PAD). The distribution and deposition of the MLG was examined using the specific antibody BG-1 and captured using fluorescence and transmission electron microscopy (TEM). RESULTS: The cellulose synthase gene superfamily contains 13 CesA and 35 Csl genes in Setaria. Transcript profiling of CslF, CslH and CslJ gene families across a vegetative tissue series indicated that SvCslF6 transcripts were the most abundant relative to all other Csl transcripts. The amounts of (1,3;1,4)-ß-glucan in Setaria vegetative tissues ranged from 0.2% to 2.9% w/w with much smaller amounts in developing grain (0.003% to 0.013% w/w). In general, the amount of (1,3;1,4)-ß-glucan was greater in younger than in older tissues. The DP3:DP4 ratios varied between tissue types and across developmental stages, and ranged from 2.4 to 3.0:1. The DP3:DP4 ratios in developing grain ranged from 2.5 to 2.8:1. Micrographs revealing the distribution of (1,3;1,4)-ß-glucan in walls of different cell types and the data were consistent with the quantitative (1,3;1,4)-ß-glucan assays. CONCLUSION: The characteristics of the cellulose synthase gene superfamily and the accumulation and distribution of (1,3;1,4)-ß-glucans in Setaria are similar to those in other C4 grasses, including sorghum. This suggests that Setaria is a suitable model plant for cell wall polysaccharide biology in C4 grasses.

Distribution, structure and biosynthetic gene families of (1,3;1,4)-ß-glucan in Sorghum bicolor.

In cereals, the presence of soluble polysaccharides including (1,3;1,4)-ß-glucan has downstream implications for human health, animal feed and biofuel applications. Sorghum bicolor (L.) Moench is a versatile crop, but there are limited reports regarding the content of such soluble polysaccharides. Here, the amount of (1,3;1,4)-ß-glucan present in sorghum tissues was measured using a Megazyme assay. Very low amounts were present in the grain, ranging from 0.16%-0.27% (w/w), while there was a greater quantity in vegetative tissues at 0.12-1.71% (w/w). The fine structure of (1,3;1,4)-ß-glucan, as denoted by the ratio of cellotriosyl and cellotetraosyl residues, was assessed by high performance liquid chromatography (HPLC) and ranged from 2.6-3:1 in the grain, while ratios in vegetative tissues were lower at 2.1-2.6:1. The distribution of (1,3;1,4)-ß-glucan was examined using a specific antibody and observed with fluorescence and transmission electron microscopy. Micrographs showed a variable distribution of (1,3;1,4)-ß-glucan influenced by temporal and spatial factors. The sorghum orthologs of genes implicated in the synthesis of (1,3;1,4)-ß-glucan in other cereals, such as the Cellulose synthase-like (Csl) F and H gene families were defined. Transcript profiling of these genes across sorghum tissues was carried out using real-time quantitative polymerase chain reaction, indicating that, as in other cereals, CslF6 transcripts dominated.

Exploring aquaporin functions during changes in leaf water potential.

Maintenance of optimal leaf tissue humidity is important for plant productivity and food security. Leaf humidity is influenced by soil and atmospheric water availability, by transpiration and by the coordination of water flux across cell membranes throughout the plant. Flux of water and solutes across plant cell membranes is influenced by the function of aquaporin proteins. Plants have numerous aquaporin proteins required for a multitude of physiological roles in various plant tissues and the membrane flux contribution of each aquaporin can be regulated by changes in protein abundance, gating, localisation, post-translational modifications, protein:protein interactions and aquaporin stoichiometry. Resolving which aquaporins are candidates for influencing leaf humidity and determining how their regulation impacts changes in leaf cell solute flux and leaf cavity humidity is challenging. This challenge involves resolving the dynamics of the cell membrane aquaporin abundance, aquaporin sub-cellular localisation and location-specific post-translational regulation of aquaporins in membranes of leaf cells during plant responses to changes in water availability and determining the influence of cell signalling on aquaporin permeability to a range of relevant solutes, as well as determining aquaporin influence on cell signalling. Here we review recent developments, current challenges and suggest open opportunities for assessing the role of aquaporins in leaf substomatal cavity humidity regulation.

A high-throughput yeast approach to characterize aquaporin permeabilities: Profiling the Arabidopsis PIP aquaporin sub-family.

Introduction: Engineering membrane transporters to achieve desired functionality is reliant on availability of experimental data informing structure-function relationships and intelligent design. Plant aquaporin (AQP) isoforms are capable of transporting diverse substrates such as signaling molecules, nutrients, metalloids, and gases, as well as water. AQPs can act as multifunctional channels and their transport function is reliant on many factors, with few studies having assessed transport function of specific isoforms for multiple substrates. Methods: High-throughput yeast assays were developed to screen for transport function of plant AQPs, providing a platform for fast data generation and cataloguing of substrate transport profiles. We applied our high-throughput growth-based yeast assays to screen all 13 Arabidopsis PIPs (AtPIPs) for transport of water and several neutral solutes: hydrogen peroxide (H2O2), boric acid (BA), and urea. Sodium (Na+) transport was assessed using elemental analysis techniques. Results: All AtPIPs facilitated water and H2O2 transport, although their growth phenotypes varied, and none were candidates for urea transport. For BA and Na+ transport, AtPIP2;2 and AtPIP2;7 were the top candidates, with yeast expressing these isoforms having the most pronounced toxicity response to BA exposure and accumulating the highest amounts of Na+. Linking putative AtPIP isoform substrate transport profiles with phylogenetics and gene expression data, enabled us to align possible substrate preferences with known and hypothesized biological roles of AtPIPs. Discussion: This testing framework enables efficient cataloguing of putative transport functionality of diverse AQPs at a scale that can help accelerate our understanding of AQP biology through big data approaches (e.g. association studies). The principles of the individual assays could be further adapted to test additional substrates. Data generated from this framework could inform future testing of AQP physiological roles, and address knowledge gaps in structure-function relationships to improve engineering efforts.

Arabidopsis plasma membrane intrinsic protein (AtPIP2;1) is implicated in a salinity conditional influence on seed germination.

Dynamic changes in aquaporin gene expression occur during seed germination. One example is the ~30-fold increase in Arabidopsis thaliana PIP2;1 transcripts within 24h of seed imbibition. To investigate whether AtPIP2;1 can influence seed germination wild-type Columbia-0, single (Atpip2;1 ) and double (Atpip2;1-Atpip2;2 ) loss-of-function mutants, along with transgenic 2x35S::AtPIP2;1 over-expressing (OE) lines and null-segregant controls, were examined. The various genotypes were germinated in control and saline (75mM NaCl treatment) conditions and tested for germination efficiency, imbibed seed maximum cross sectional (MCS) area, imbibed seed mass, and seed Na+ and K+ content. Seed lacking functional AtPIP2;1 and/or AtPIP2;2 proteins or constitutively over-expressing AtPIP2;1 , had delayed germination in saline conditions relative to wild-type and null-segregant seed, respectively. Exposure to saline germination conditions resulted in Atpip2;1 mutants having greater imbibed seed mass and less accumulated Na+ than wild-type, whereas lines over-expressing AtPIP2;1 had reduced imbibed seed mass and greater seed K+ content than null-segregant control seed. The results imply a role for AtPIP2;1 in seed germination processes, whether directly through its capacity for water and ion transport or H2 O2 signalling, or indirectly through potentially triggering dynamic differential regulation of other aquaporins expressed during germination. Future research will aid in dissecting the aquaporin functions influencing germination and may lead to novel solutions for optimising germination in sub-optimal conditions, such as saline soils.

Major genes for Na+ exclusion, Nax1 and Nax2 (wheat HKT1;4 and HKT1;5), decrease Na+ accumulation in bread wheat leaves under saline and waterlogged conditions.

Two major genes for Na(+) exclusion in durum wheat, Nax1 and Nax2, that were previously identified as the Na(+) transporters TmHKT1;4-A2 and TmHKT1;5-A, were transferred into bread wheat in order to increase its capacity to restrict the accumulation of Na(+) in leaves. The genes were crossed from tetraploid durum wheat (Triticum turgidum ssp. durum) into hexaploid bread wheat (Triticum aestivum) by interspecific crossing and marker-assisted selection for hexaploid plants containing one or both genes. Nax1 decreased the leaf blade Na(+) concentration by 50%, Nax2 decreased it by 30%, and both genes together decreased it by 60%. The signature phenotype of Nax1, the retention of Na(+) in leaf sheaths resulting in a high Na(+) sheath:blade ratio, was found in the Nax1 lines. This conferred an extra advantage under a combination of waterlogged and saline conditions. The effect of Nax2 on lowering the Na(+) concentration in bread wheat was surprising as this gene is very similar to the TaHKT1;5-D Na(+) transporter already present in bread wheat, putatively at the Kna1 locus. The results indicate that both Nax genes have the potential to improve the salt tolerance of bread wheat.

C4 plants as biofuel feedstocks: optimising biomass production and feedstock quality from a lignocellulosic perspective.

The main feedstocks for bioethanol are sugarcane (Saccharum officinarum) and maize (Zea mays), both of which are C(4) grasses, highly efficient at converting solar energy into chemical energy, and both are food crops. As the systems for lignocellulosic bioethanol production become more efficient and cost effective, plant biomass from any source may be used as a feedstock for bioethanol production. Thus, a move away from using food plants to make fuel is possible, and sources of biomass such as wood from forestry and plant waste from cropping may be used. However, the bioethanol industry will need a continuous and reliable supply of biomass that can be produced at a low cost and with minimal use of water, fertilizer and arable land. As many C(4) plants have high light, water and nitrogen use efficiency, as compared with C(3) species, they are ideal as feedstock crops. We consider the productivity and resource use of a number of candidate plant species, and discuss biomass 'quality', that is, the composition of the plant cell wall.

An algal PIP-like aquaporin facilitates water transport and ionic conductance.

Aquaporins are water and solute channel proteins found throughout the kingdoms of life. Ion-conducting aquaporins (icAQPs) have been identified in both plants and animals indicating that this function may be conserved through evolution. In higher plants icAQP function has been demonstrated for isoforms from two of five aquaporin subfamilies indicating that this function could have existed before the divergence of higher plants from green algae. Here a PIP-like aquaporin from the charophytic alga Klebsormidium nitens was functionally characterised in Xenopus laevis oocytes and its expression was found to induce water and ion conductance.