Dosage differences in 12-OXOPHYTODIENOATE REDUCTASE genes modulate wheat root growth.

Wheat, an essential crop for global food security, is well adapted to a wide variety of soils. However, the gene networks shaping different root architectures remain poorly understood. We report here that dosage differences in a cluster of monocot-specific 12-OXOPHYTODIENOATE REDUCTASE genes from subfamily III (OPRIII) modulate key differences in wheat root architecture, which are associated with grain yield under water-limited conditions. Wheat plants with loss-of-function mutations in OPRIII show longer seminal roots, whereas increased OPRIII dosage or transgenic over-expression result in reduced seminal root growth, precocious development of lateral roots and increased jasmonic acid (JA and JA-Ile). Pharmacological inhibition of JA-biosynthesis abolishes root length differences, consistent with a JA-mediated mechanism. Transcriptome analyses of transgenic and wild-type lines show significant enriched JA-biosynthetic and reactive oxygen species (ROS) pathways, which parallel changes in ROS distribution. OPRIII genes provide a useful entry point to engineer root architecture in wheat and other cereals.

A genome-wide association study unveils key chromosome regions involved in determining sodium accumulation in wheat under conditions of low potassium supply.

Improving nutrient use efficiency is an important objective in modern breeding programs. In this work, we examined potassium utilization efficiency (KUtE) and traits potentially related to it in a formerly genotyped, geographically diverse population of bread wheat (Triticum aestivum) under low potassium supply conditions. Our results unveil the existence of a large variation within the population for the traits examined. A genome-wide association study, based on a single-locus model, identified 15 markers associated with some of those traits. No marker-trait association was found using that tool for KUtE, but the use of a multi-locus approach suggested that additional marker-trait associations may be present, including whole-plant KUtE. Besides, the existence of a significant correlation between KUtE and sodium accumulation in shoots suggests the possibility of pyramiding traits associated with sodium homeostasis to improve this efficiency. In this regard, two discrete regions mapped on the long arm of chromosome 1B (1BLA and 1BLB) were associated with variation in sodium accumulation as detected with the single and multi-locus models used. Further exploration of the potential function of the genes placed in these regions, and their expression patterns, suggested likely candidates for this trait. Among the candidates placed in 1BLA region, we found TraesCS1B02G370500, TraesCS1B02G370600, and TraesCS1B02G370900, coding for putative Calcineurin B like proteins. Region 1BLB contain TraesCS1B02G388900 coding for a kinase and other genes including TraesCS1B02G389700, TraesCS1B02G389800 and TraesCS1B02G389900 coding for Ethylene-responsive transcription factors. The information here provided can be useful in breeding programs aimed to manipulate sodium accumulation through marker-assisted selection.

Barley plants carrying the altered function Sln1d allele display modified responses to low phosphorus supply: implications for phosphorus utilisation efficiency.

The module GA-GID1-DELLA (Gibberellin-Gibberellin Receptor-DELLA proteins) provides a point for the integration of signals potentially relevant in determining nutrient utilisation and acquisition efficiencies. In this study, we explored the role of components of this module during the acclimation of barley plants (Hordeum vulgare L.) to different phosphorus (P) supplies by using two related genotypes, harbouring either the WT or the Sln1d alleles of the DELLA-coding gene Sln1. Dwarf Sln1d plants exhibited reduced shoot P utilisation efficiency (PUtE) and better performance at low levels of P supply. The superior PUtE displayed by WT plants disappeared when corrected by internal P concentration, indicating that multiple analyses are necessary to fully understand the meaning of PUtE estimates. Over a wide range of external supplies of P, Sln1d plants displayed enhanced P concentration, which was associated with low relative growth rate, high biomass partitioning to roots and high P-uptake-rate, thus suggesting that the effect of the Sln1d allele on P dynamics is not simply a consequence of slow growth habit. An enhanced P concentration was also found in a mutant with defective GAs-synthesis. Our results suggest that components of the GA-GID1-DELLAs module contribute to set the acclimation response of barley plants to low P supply through both P-dynamics dependent and P-dynamics independent mechanisms.

A wheat/rye polymorphism affects seminal root length and yield across different irrigation regimes.

The introgression of a small segment of wheat (Triticum aestivum L.) chromosome arm 1BS in the distal region of the rye (Secale cereale L.) 1RS.1BL arm translocation in wheat (henceforth 1RSRW) was previously associated with reduced grain yield, carbon isotope discrimination, and stomatal conductance, suggesting reduced access to soil moisture. Here we show that lines with the normal 1RS arm have longer roots than lines with the 1RSRW arm in both field and hydroponic experiments. In the 1RSRW lines, differences in seminal root length were associated with a developmentally regulated arrest of the root apical meristem (RAM). Approximately 10 d after germination, the seminal roots of the 1RSRW plants showed a gradual reduction in elongation rate, and stopped growing a week later. Seventeen days after germination, the roots of the 1RSRW plants showed altered gradients of reactive oxygen species and emergence of lateral roots close to the RAM, suggesting changes in the root meristem. The 1RSRW lines also showed reduced biomass (estimated by the normalized difference vegetation index) and grain yield relative to the 1RS lines, with larger differences under reduced or excessive irrigation than under normal irrigation. These results suggest that this genetic variation could be useful to modulate root architecture.

Root phenotypes of dwarf and "overgrowth" SLN1 barley mutants, and implications for hypoxic stress tolerance.

Gibberellins are central to the regulation of plant development and growth. Action of gibberellins involves the degradation of DELLA proteins, which are negative regulators of growth. In barley (Hordeum vulgare), certain mutations affecting genes involved in gibberellin synthesis or coding for the barley DELLA protein (Sln1) confer dwarfism. Recent studies have identified new alleles of Sln1 with the capacity to revert the dwarf phenotype back to the taller phenotypes. While the effect of these overgrowth alleles on shoot phenotypes has been explored, no information is available for roots. Here, we examined aspects of the root phenotypes displayed by plants with various Sln1 gene alleles, and tested responses to growth in an O2-deficient root-zone as occurs during soil waterlogging. One overgrowth line, bearing the Sln1d.8 allele carrying two amino acid substitutions (one in the amino terminus and one in the GRAS domain of the encoded DELLA protein), displays profound and opposite effects on shoot height and root length. While it stimulates shoot height, it severely compromises root length by a reduction of cell size in zones distal to the root apex. In addition, Sln1d.8 plants counteract the negative effect of the original mutation on the formation of adventitious roots. Interestingly, plants bearing this allele display enhanced resistance to flooding stress in a way non-related with increased root porosity. Thus, various Sln1 gene alleles contribute to root phenotypes and can also influence plant responses to root-zone O2-deficiency stress.

A survey of sequences of KT-HAK-KUP transporters in green algae and basal land plants.

In this data article, information is provided on sequences of KT-HAK-KUP transporters from green algae and basal land plants. A data set is offered containing sequences corresponding to the chlorophyte algae Chlamydomonas eustigma, Gonium pectorale and Coccomyxa subellipsoidea, the charophyte algae Coleochaete orbicularis and Klebsormidium flaccidum, the bryophyte Sphagnum fallax, the marchantophyte Marchantia polymorpha and the gymnosperm Pinus taeda, which have been not formerly analyzed. In addition, an analysis of similarity scores among representatives of the clusters recognized in photosynthetic green organisms (namely, chlorophyte algae, charophyte algae, basal embryophytes and higher embryophytes) is performed as well as an analysis of membrane topology for them.

KT-HAK-KUP transporters in major terrestrial photosynthetic organisms: A twenty years tale.

Since their discovery, twenty years ago, KT-HAK-KUP transporters have become a keystone to understand how alkali cation fluxes are controlled in major land-dwelling photosynthetic organisms. In this review we focus on their discovery, phylogeny, and functions, as well as the regulation of its canonical member, AtHAK5. We also address issues related to structure-function studies, and the technological possibilities opened up by recent findings. Available evidence suggests that this family of transporters underwent an early divergence into major groups following the conquest of land by embryophytes. KT-HAK-KUPs are necessary to accomplish several major developmental and growth processes, as well as to ensure plant responses to environmental injuries. Although the primary function of these transporters is to mediate potassium (K+) fluxes, some of them can also mediate sodium (Na+) and cesium (Cs+) transport, and contribute to maintenance of K+ (and Na+) homeostasis in different plant tissues. In addition, there is evidence for a role of some members of this family in auxin movement and in adenylate cyclase activity. Recent research, focusing on the regulation of the canonical member of this family, AtHAK5, revealed the existence of a complex network that involves transcriptional and post-transcriptional phenomena which control the enhancement of AtHAK5-mediated K+ uptake when Arabidopsis thaliana plants are faced with low K+ supply. In spite of the formidable advances made since their discovery, important subjects remain to be elucidated to gain a more complete knowledge of the roles and regulation of KT-HAK-KUPs, as well as to improve their use for innovative procedures in crop breeding.

The stay-green phenotype of TaNAM-RNAi wheat plants is associated with maintenance of chloroplast structure and high enzymatic antioxidant activity.

TaNAM transcription factors play an important role in controlling senescence, which in turn, influences the delivery of nitrogen, iron and other elements to the grain of wheat (Triticum aestivum) plants, thus contributing to grain nutritional value. While lack or diminished expression of TaNAMs determines a stay-green phenotype, the precise effect of these factors on chloroplast structure has not been studied. In this work we focused on the events undergone by chloroplasts in two wheat lines having either control or diminished TaNAM expression due to RNA interference (RNAi). It was found that in RNAi plants maintenance of chlorophyll levels and maximal photochemical efficiency of photosystem II were associated with lack of chloroplast dismantling. Flow cytometer studies and electron microscope analysis showed that RNAi plants conserved organelle ultrastructure and complexity. It was also found that senescence in control plants was accompanied by a low leaf enzymatic antioxidant activity. Lack of chloroplast dismantling in RNAi plants was associated with maintenance of protein and iron concentration in the flag leaf, the opposite being observed in control plants. These data provide a structural basis for the observation that down regulation of TaNAMs confers a functional stay-green phenotype and indicate that the low export of iron and nitrogen from the flag leaf of these plants is concomitant, within the developmental window studied, with lack of chloroplast degradation and high enzymatic antioxidant activity.

Internal efficiency of nutrient utilization: what is it and how to measure it during vegetative plant growth?

Efficient use of the resources required by plants to sustain crop production is considered an important objective in agriculture. In this context, the idea of developing crops with an enhanced ability to utilize mineral nutrients already taken up by roots has been proposed. In recent years powerful tools that allow the association of phenotypic variation with high-resolution genetic maps of crop plants have also emerged. To take advantage of these tools, accurate methods are needed to estimate the internal efficiency of nutrient utilization (ENU) at the whole-plant level, which requires using suitable conceptual and experimental approaches. Here we highlight some inconsistencies in the definitions of ENU commonly used for ENU 'phenotyping' at the vegetative stage and suggest that it would be convenient to adopt a dynamic definition. The idea that ENU should provide information about the relationship between carbon and mineral nutrient economies mainly during the period under which growth is actually affected by low internal nutrient concentration is here advocated as a guide for the selection of adequate operational ENU formulae for the vegetative stage. The desirability of using experimental approaches that allow removal of the influence of nutrient acquisition efficiency on ENU estimations is highlighted. It is proposed that the use of simulation models could help refine the conclusions obtained through these experimental procedures. Some potential limitations in breeding for high ENU are also considered.

An exogenous source of nitric oxide modulates zinc nutritional status in wheat plants.

The effect of addition of the nitric oxide donor S-nitrosoglutathione (GSNO) on the Zn nutritional status was evaluated in hydroponically-cultured wheat plants (Triticum aestivum cv. Chinese Spring). Addition of GSNO in Zn-deprived plants did not modify biomass accumulation but accelerated leaf senescence in a mode concomitant with accelerated decrease of Zn allocation to shoots. In well-supplied plants, Zn concentration in both roots and shoots declined due to long term exposure to GSNO. A further evaluation of net Zn uptake rate (ZnNUR) during the recovery of long-term Zn-deprivation unveiled that enhanced Zn-accumulation was partially blocked when GSNO was present in the uptake medium. This effect on uptake was mainly associated with a change of Zn translocation to shoots. Our results suggest a role for GSNO in the modulation of Zn uptake and in root-to-shoot translocation during the transition from deficient to sufficient levels of Zn-supply.

A theoretical framework to study potassium utilization efficiency in response to withdrawal of potassium.

An important objective of plant research is to improve the efficiency in the utilization of major nutrients, particularly nitrogen, phosphorus, and potassium. Several definitions of internal nutrient utilization efficiency (NUE) have been proposed, but the theoretical consistence of their use has been poorly explored. Here, a non-mechanistic approach was developed to theoretically examine the dynamics of commonly used NUE indicators following complete potassium deprivation. This approach was used to study the sensitivity of NUE indicators to changes in the actual NUE (NUEa) of K(+) in virtual plants. Three empirically based models that differ in the relationship between NUE and the internal K(+) concentration were examined. Frequently used indicators (potassium use efficiency, utilization efficiency, physiological efficiency, and nutrient productivity) and two additional ones introduced here (accumulated productivity and physiological ratio) differed in their capacity to reflect differences in NUEa. They also exhibited large disparities in their temporal variation and in their responsiveness to the concentration of K(+) before the beginning of the deprivation period. According to this analysis, the simultaneous use of several indicators could help to refine plant breeding for high NUE. The data also suggest that a trade off between plant productivity and the time necessary to reduce the concentration of K(+) by half is inherent to the dynamics of plant systems. Finally, it is proposed that for some plant species selection for high NUEa would not always be in conflict with selection for improved relative plant performance in low K(+) environments.

Near-isogenic wheat lines carrying altered function alleles of the Rht-1 genes exhibit differential responses to potassium deprivation.

Most of the elements involved in the integration of signals of low external K(+)-supply into a physiological response pathway remain essentially unknown. The aim of this work was to study the influence exerted by DELLA proteins, which are known to be key components for the control of growth, on plant responses during K(+) deprivation in wheat (Triticum aestivum) by using two sets of near-isogenic lines (NILs) in the Maringa and April Bearded cultivars. After K(+) shortage, the NILs of both cultivars containing the Rht-B1b,Rht-D1b alleles, which encode altered function DELLA proteins, displayed either a slight or no decrease in chlorophyll content, in contrast to the sharp decrease observed in the NILs having the wild type alleles (Rht-B1a,Rht-D1a). That difference was accompanied by a lower relative decrease of biomass accumulation only in the Maringa cultivar. In both cultivars, high chlorophyll retention was coupled with K(+) starvation-induced differences in superoxide dismutase and ascorbate peroxidase activities, which were enhanced in K(+)-starved Rht-B1b,Rht-D1b NILs. In addition, Rht-B1b,Rht-D1b and Rht-B1a,Rht-D1a NILs markedly differed in the accumulation of the major cations Ca(2+), Na(+) and K(+). These results suggest a major role of the Rht-1 genes in the control of physiological responses during K(+) deprivation.