Bio-available zinc in rice seeds is increased by activation tagging of nicotianamine synthase

We generated rice lines with increased content of nicotianamine (NA), a key ligand for metal transport and homeostasis. This was accomplished by activation tagging of rice nicotianamine synthase 2 (OsNAS2). Enhanced expression of the gene resulted in elevated NA levels, greater Zn accumulations and improved plant tolerance to a Zn deficiency. Expression of Zn-uptake genes and those for the biosynthesis of phytosiderophores (PS) were increased in transgenic plants. This suggests that the higher amount of NA led to greater exudation of PS from the roots, as well as stimulated Zn uptake, translocation and seed-loading. In the endosperm, the OsNAS2 activation-tagged line contained up to 20-fold more NA and 2.7-fold more zinc. Liquid chromatography combined with inductively coupled plasma mass spectrometry revealed that the total content of zinc complexed with NA and 2'-deoxymugineic acid was increased 16-fold. Mice fed with OsNAS2-D1 seeds recovered more rapidly from a zinc deficiency than did control mice receiving WT seeds. These results demonstrate that the level of bio-available zinc in rice grains can be enhanced significantly by activation tagging of OsNAS2.     

The mitogenome of Onchocerca volvulus from the Brazilian Amazonia focus

We report here the first complete mitochondria genome of Onchocerca volvulus from a focus outside of Africa. An O. volvulus mitogenome from the Brazilian Amazonia focus was obtained using a combination of high-throughput and Sanger sequencing technologies. Comparisons made between this mitochondrial genome and publicly available mitochondrial sequences identified 46 variant nucleotide positions and suggested that our Brazilian mitogenome is more closely related to Cameroon-origin mitochondria than West African-origin mitochondria. As well as providing insights into the origins of Latin American onchocerciasis, the Brazilian Amazonia focus mitogenome may also have value as an epidemiological resource.     

Anticipation or ascertainment bias in schizophrenia? Penrose's familial mental illness sample.

Several studies have observed anticipation (earlier age at onset [AAO] in successive generations) in familial schizophrenia. However, whether true anticipation or ascertainment bias is the principal originating mechanism remains unclear. In 1944 L. S. Penrose collected AAO data on a large, representative sample of familial mental illness, using a broad ascertainment strategy. These data allowed examination of anticipation and ascertainment biases in five two-generation samples of affected relative pairs. The median intergenerational difference (MID) in AAO was used to assess anticipation. Results showed significant anticipation in parent-offspring pairs with schizophrenia (n = 137 pairs; MID 15 years; P = .0001) and in a positive control sample with Huntington disease (n = 11; P = .01). Broadening the diagnosis of the schizophrenia sample suggested anticipation of severity of illness. However, other analyses provided evidence for ascertainment bias, especially in later-AAO parents, in parent-offspring pairs. Aunt/uncle-niece/nephew schizophrenia pairs showed anticipation (n = 111; P = .0001), but the MID was 8 years and aunts/uncles had earlier median AAO than parents. Anticipation effects were greatest in pairs with late-AAO parents but remained significant in a subgroup of schizophrenia pairs with early parental AAO (n = 31; P = .03). A small control sample of other diseases had MID of 5 years but no significant anticipation (n = 9; P = .38). These results suggest that, although ascertainment-bias effects were observed in parent-offspring pairs, true anticipation appears to be inherent in the transmission of familial schizophrenia. The findings support investigations of unstable mutations and other mechanisms that may contribute to true anticipation in schizophrenia.     

Sensitive Detection of Phosphorus Deficiency in Plants Using Chlorophyll a Fluorescence

Phosphorus (P) is a finite natural resource and an essential plant macronutrient with major impact on crop productivity and global food security. Here, we demonstrate that time-resolved chlorophyll a fluorescence is a unique tool to monitor bioactive P in plants and can be used to detect latent P deficiency. When plants suffer from P deficiency, the shape of the time-dependent fluorescence transients is altered distinctively, as the so-called I step gradually straightens and eventually disappears. This effect is shown to be fully reversible, as P resupply leads to a rapid restoration of the I step. The fading I step suggests that the electron transport at photosystem I (PSI) is affected in P-deficient plants. This is corroborated by the observation that differences at the I step in chlorophyll a fluorescence transients from healthy and P-deficient plants can be completely eliminated through prior reduction of PSI by far-red illumination. Moreover, it is observed that the barley (Hordeum vulgare) mutant Viridis-zb⁶³, which is devoid of PSI activity, similarly does not display the I step. Among the essential plant nutrients, the effect of P deficiency is shown to be specific and sufficiently sensitive to enable rapid in situ determination of latent P deficiency across different plant species, thereby providing a unique tool for timely remediation of P deficiency in agriculture.The world population is estimated to exceed 9 billion people by 2050. This means that agriculture on a global scale has to increase food production by 70% to 100%, and, at the same time, handle the consequences of global climate changes and reduce its environmental footprint (Food and Agriculture Organization of the United Nations, 2009; Godfray et al., 2010; Foley et al., 2011). A major challenge related to this is the supply and use of phosphorus (P) to support future plant production (Cordell et al., 2009; Gilbert, 2009; MacDonald et al., 2011).P is an essential plant nutrient, which means that plants require P in adequate amounts to fulfill a complete lifecycle. It has been estimated that 30% of the world’s agricultural soils are P deficient and need fertilizer addition to ensure yield and quality (MacDonald et al., 2011). However, phosphate rock, the main source of P fertilizers, is a finite natural resource, and the known rock phosphate reserves are estimated to last as little as 50 years in the gloomiest forecasts (Gilbert, 2009; Edixhoven et al., 2013). This makes P a potential strategic natural resource similar to oil, as very few countries control the vast majority of the known reserves (Gilbert, 2009; Elser and Bennett, 2011; Edixhoven et al., 2013). Presently, an immense overuse of P is found in some parts of the world, causing eutrophication of lakes and seas, while P depletion results in severe yield limitations elsewhere (MacDonald et al., 2011; Obersteiner et al., 2013). An essential aspect of solving both of these problems is to increase P use efficiency in agriculture, thus reducing the negative environmental impact of agriculture and helping to ensure a sustainable use of P resources while increasing the worldwide food production (Schröder et al., 2011; Veneklaas et al., 2012).Here, we present a unique analytical principle based on chlorophyll a fluorescence that allows rapid, nondestructive, onsite assessment of plant P status by recording the so-called OJIP transient of a dark-adapted leaf.When a chlorophyll molecule absorbs light, one of three events will occur: The light may be used to drive photosynthesis, it can be dissipated as heat, or it can be reemitted as fluorescence. Less than 10% of light absorbed by the plant causes emission of chlorophyll a fluorescence (Govindjee, 2004; Stirbet and Govindjee, 2011). When a dark-adapted leaf is exposed to saturating actinic light, the resulting time-dependent fluorescence forms a so-called Kautsky curve (Kautsky and Hirsch, 1931; McAlister and Myers, 1940). Within 300 ms, the fluorescence increases from a minimum level (F₀) to the maximum level. If measured with a sufficiently high time resolution, a polyphasic transient with four distinct steps, designated as O, J, I, and P, is observed. After reaching maximum intensity at the P step, the fluorescence intensity declines until it reaches a steady state within a few minutes (Harbinson and Rosenqvist, 2003; Govindjee, 2004).The physiological mechanisms underlying the polyphasic OJIP transient are still not clarified, but it is believed that the J and I steps represent dynamic bottlenecks in the photosynthetic electron transport chain. The first rise (2 ms) from O to J is referred to as the photochemical phase due to its dependence on the intensity of the incoming light. This phase is assumed to reflect the reduction of the primary quinone electron acceptor in PSII (Stirbet and Govindjee, 2011). The reduction of the primary quinone electron acceptor results in a decreased electron trapping efficiency and therefore an increase in the dissipation of absorbed light energy by fluorescence and heat. The second part, from J over I to P, is called the thermal phase due to its temperature sensitivity. This phase is much slower than the first, and it is believed that the J-I phase primarily reflects a sequential reduction of the remaining plastoquinone pool of PSII and that the I-P phase reflects the subsequent electron flow through cytochrome b₆f to electron sinks at the PSI acceptor side (Stirbet and Govindjee, 2011). Thus, the OJIP transient resembles a titration of the photochemical quantum yield and reflects the complex electron transport properties of PSII and PSI.Consistent with their known influence on photosynthesis, deficiencies of essential plant nutrients such as Fe, Cu, Mg, Mn, and S have previously been shown to affect OJIP transients (Kastori et al., 2000; Mallick and Mohn, 2003; Larbi et al., 2004; Husted et al., 2009; Tang et al., 2012; Yang et al., 2012). As a consequence, several attempts have been made to identify nutrient imbalances and disorders using one or several parameters derived from the transients, but apart from Mn (Husted et al., 2009; Schmidt et al., 2013), attempts have not been successful in terms of sensitivity and specificity. This includes P, which previously has been reported to have an effect on OJIP transients, yet the reported effects seem mutually contradictory and nonspecific to P (Ripley et al., 2004; Weng et al., 2008; Jiang et al., 2009; Lin et al., 2009).Here, we present the unique finding that increasing levels of P deficiency affect the shape of the OJIP transient around the I step at 20 to 50 ms and causes the I step to gradually straighten and disappear. It is demonstrated that this effect is fully reversible and, among the essential plant nutrients, specific for P deficiency using both monocotyledons (barley [Hordeum vulgare]) and dicotyledons (tomato [Solanum lycopersicum]) plant species. Furthermore, it is shown that it is possible to determine whether a plant is P sufficient or deficient and to quantitatively predict the P concentration in leaf tissue using multivariate analysis of the OJIP transients.     

Manganese efficiency in barley: identification and characterization of the metal ion transporter HvIRT1

Manganese (Mn) deficiency is an important plant nutritional disorder in many parts of the world. Barley (Hordeum vulgare) genotypes differ considerably in their ability to grow in soils with low Mn(2+) availability. Differential genotypic Mn efficiency can be attributed to differences in Mn(2+) uptake kinetics in the low nanomolar concentration range. However, the molecular basis for these differences has not yet been clarified. We present here the identification and characterization of the first barley gene encoding a plasma membrane-localized metal transport protein able to transport Mn(2+). The gene is designated HvIRT1 (for IRON-REGULATED TRANSPORTER1) because it belongs to the ZIP gene family and has a high similarity to rice (Oryza sativa) OsIRT1. A novel yeast uptake assay based on inductively coupled plasma-mass spectrometry analysis of 31 different metal and metalloid ions showed that the HvIRT1 protein, in addition to Mn(2+), also transported Fe(2+)/Fe(3+), Zn(2+), and Cd(2+). Both Mn and iron deficiency induced an up-regulation of HvIRT1 in two barley genotypes differing in Mn efficiency, but the expression levels in all cases were highest (up to 40%) in the Mn-efficient genotype. The higher expression of HvIRT1 correlated with an increased Mn(2+) uptake rate. We conclude that HvIRT1 is an important component controlling Mn(2+) uptake in barley roots and contributes to genotypic differences in Mn(2+) uptake kinetics.     

Latent manganese deficiency in barley can be diagnosed and remediated on the basis of chlorophyll a fluorescence measurements

Background and aims

Manganese (Mn) deficiency represents a major plant nutritional disorder in winter cereals. The deficiency frequently occurs latently and the lack of visual symptoms prevents timely remediation and cause significant yield reductions. These problems prompted us to investigate chlorophyll (Chl) a fluorescence as a tool for diagnosis of latent Mn deficiency.

Methods

Barley plants grown under controlled greenhouse conditions or in the field were exposed to different intensities of Mn deficiency. The responses were characterised by analysis of Chl a fluorescence, photosystem II (PSII) proteins and mineral elements.

Results

Analysis of the Chl a fluorescence induction kinetics (FIK) revealed distinct changes long before any visual symptoms of Mn deficiency were apparent. The changes were specific for Mn and did not occur in Mg, S, Fe or Cu deficient plants. The changes in Mn deficient plants were accompanied by a marked reduction of the D1 protein in PSII. Foliar Mn application fully restored PSII functionality, ensured winter survival, and increased grain yields under field conditions.

Conclusions

The efficiency and stability of PSII are markedly affected by latent Mn deficiency. Chlorophyll a fluorescence measurements constitute a powerful and valuable tool for diagnosis and remediation of latent Mn deficiency.