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Abstract Background Arbuscular mycorrhizas (AM) are widespread symbioses that provide great advantages to the plant, improving its nutritional status and allowing the fungus to complete its life cycle. Nevertheless, molecular mechanisms that lead to the development of AM symbiosis are not yet fully deciphered. Here, we have focused on two putative aquaporin genes, LjNIP1 and LjXIP1, which resulted to be upregulated in a transcriptomic analysis performed on mycorrhizal roots of Lotus japonicus. Results A phylogenetic analysis has shown that the two putative aquaporins belong to different functional families: NIPs and XIPs. Transcriptomic experiments have shown the independence of their expression from their nutritional status but also a close correlation with mycorrhizal and rhizobial interaction. Further transcript quantification has revealed a good correlation between the expression of one of them, LjNIP1, and LjPT4, the phosphate transporter which is considered a marker gene for mycorrhizal functionality. By using laser microdissection, we have demonstrated that one of the two genes, LjNIP1, is expressed exclusively in arbuscule-containing cells. LjNIP1, in agreement with its putative role as an aquaporin, is capable of transferring water when expressed in yeast protoplasts. Confocal analysis have demonstrated that eGFP-LjNIP1, under its endogenous promoter, accumulates in the inner membrane system of arbusculated cells. Conclusions Overall, the results have shown different functionality and expression specificity of two mycorrhiza-inducible aquaporins in L. japonicus. One of them, LjNIP1 can be considered a novel molecular marker of mycorrhizal status at different developmental stages of the arbuscule. At the same time, LjXIP1 results to be the first XIP family aquaporin to be transcriptionally regulated during symbiosis.

Conventional wheat production utilizes fertilizers of various nitrogen forms. Sole ammonium nutrition has been shown to improve grain quality, despite the potential toxic effects of ammonium at elevated concentrations. We therefore investigated the responses of young seedlings of winter wheat to different nitrogen sources (NH4NO3 = NN, NH4Cl = NNH4+ and KNO3 = NNO3−). Growth with ammonium‐nitrate was superior. However, an elevated concentration of sole ammonium caused severe toxicity symptoms and significant decreases in biomass accumulation. We addressed the molecular background of the ammonium uptake by gathering an overview of the ammonium transporter (AMT) of wheat (Triticum aestivum) and characterized the putative high‐affinity TaAMT1 transporters. TaAMT1;1 and TaAMT1;2 were both active in yeast and Xenopus laevis oocytes and showed saturating high‐affinity ammonium transport characteristics. Interestingly, nitrogen starvation, as well as ammonium resupply to starved seedlings triggered an increase in the expression of the TaAMT1s. The presence of nitrate seamlessly repressed their expression. We conclude that wheat showed the ability to respond robustly to sole ammonium supply by adopting distinct physiological and transcriptional responses. [ABSTRACT FROM AUTHOR]

Background and Aims An increase in root hair length and density and the development of arbuscular mycorrhiza symbiosis are two alternative strategies of most plants to increase the root–soil surface area under phosphorus (P) deficiency. Across many plant species, root hair length and mycorrhization density are inversely correlated. Root architecture, rooting density and physiology also differ between species. This study aims to understand the relationship among root hairs, arbuscular mycorrhizal fungi (AMF) colonization, plant growth, P acquisition and mycorrhizal-specific Pi transporter gene expression in maize. Methods Using nearly isogenic maize lines, the B73 wild type and the rth3 root hairless mutant, we quantified the effect of root hairs and AMF infection in a calcareous soil under P deficiency through a combined analysis of morphological, physiological and molecular factors. Key Results Wild-type root hairs extended the rhizosphere for acid phosphatase activity by 0.5 mm compared with the rth 3 hairless mutant, as measured by in situ zymography. Total root length of the wild type was longer than that of rth3 under P deficiency. Higher AMF colonization and mycorrhiza-induced phosphate transporter gene expression were identified in the mutant under P deficiency, but plant growth and P acquisition were similar between mutant and the wild type. The mycorrhizal dependency of maize was 33 % higher than the root hair dependency. Conclusions The results identified larger mycorrhizal dependency than root hair dependency under P deficiency in maize. Root hairs and AMF inoculation are two alternative ways to increase Pi acquisition under P deficiency, but these two strategies compete with each other. [ABSTRACT FROM AUTHOR]

In plants, nutrient transporters require tight regulation to ensure optimal uptake in complex environments. The activities of many nutrient transporters are post-translationally regulated by reversible phosphorylation, allowing rapid adaptation to variable environmental conditions. Here, we show that the Arabidopsis root epidermis-expressed ammonium transporter AtAMT1;3 was dynamically (de-)phosphorylated at multiple sites in the cytosolic C-terminal region (CTR) responding to ammonium and nitrate signals. Under ammonium resupply rapid phosphorylation of a Thr residue (T464) in the conserved part of the CTR (CTRC) effectively inhibited AtAMT1;3-dependent NH4+ uptake. Moreover, phosphorylation of Thr (T494), one of three phosphorylation sites in the non-conserved part of the CTR (CRTNC), moderately decreased the NH4+ transport activity of AtAMT1;3, as deduced from functional analysis of phospho-mimic mutants in yeast, oocytes, and transgenic Arabidopsis. Double phospho-mutants indicated a role of T494 in fine-tuning the NH4+ transport activity when T464 was non-phosphorylated. Transient dephosphorylation of T494 with nitrate resupply closely paralleled a transient increase in ammonium uptake. These results suggest that T464 phosphorylation at the CTRC acts as a prime switch to prevent excess ammonium influx, while T494 phosphorylation at the CTRNC fine tunes ammonium uptake in response to nitrate. This provides a sophisticated regulatory mechanism for plant ammonium transporters to achieve optimal ammonium uptake in response to various nitrogen forms. [ABSTRACT FROM AUTHOR]

White lupin cluster roots are specialized brush‐like root structures that are formed in some species under phosphorus (P)‐deficient conditions. They intensely secrete protons and organic acid anions for solubilization and acquisition of sparingly soluble phosphates. Phytohormones and sucrose modulate cluster root number, but the molecular mechanisms of cluster root formation have been elusive. Here, a novel peptide phytohormone was identified that affects cluster root development. It belongs to the C‐TERMINALLY-ENCODED PEPTIDE (CEP) family. Members of that family arrest root growth and modulate branching in model species. LaCEP1 was highly expressed in the pre‐emergence zone of clusters. Over‐expression of the gene encoding the LaCEP1 propeptide resulted in moderate inhibition of cluster root formation. The primary and lateral root lengths of lupin were little affected by the overexpression, but LaCEP1 reduced cluster rootlet and root hair elongation. Addition of a 15‐mer core peptide derived from LaCEP1 similarly altered root morphology and modified cluster activity, suggesting that a core sequence of the propeptide is functionally sufficient. Stable overexpression in Arabidopsis confirmed the LaCEP1 function in root growth inhibition across species. Taken together, the root inhibitory effects of the LaCEP1 phytohormone suggest a role as of a regulatory module involved in cluster root development in white lupin. [ABSTRACT FROM AUTHOR]

Plants generally produce more biomass when all nutrients are available in sufficient amounts. In addition to environmental constraints, genetic and developmental factors, such as the transition from vegetative to reproductive growth, restrict maximal biomass yield. Here, we report the peculiar observation that a subset of Arabidopsis thaliana accessions produced larger shoot rosette diameters when grown in zinc (Zn)-deficient conditions, compared with Zn-sufficient conditions. This was associated with early flowering that restricted the leaf length under Zn sufficiency. Zinc deficiency repressed the expression of FLOWERING LOCUS T (FT), which encodes a major regulator of flowering. Repression or loss of FT increased the rosette diameter via a delay of the transition to flowering, a longer phase of leaf growth, and an increased leaf number. The transition to flowering reduced, but did not terminate, the proliferation of established leaves. The size of individual leaf mesophyll cells was not affected by Zn deficiency or by loss of FT, indicating that the larger rosette diameter was caused by maintained proliferation of vegetative tissue. As a consequence, early-flowering accessions under Zn deficiency grew to have larger rosette diameters due to a delay of flowering, which explains the unusual increase of vegetative biomass under nutrient deficiency. [ABSTRACT FROM AUTHOR]

Ion transport in plants is not only strictly regulated on a transcriptional level, but it is also regulated posttranslationally. Enzyme modifications such as phosphorylation provide rapid regulation of many plant ion transporters and channels. Upon exposure to high ammonium concentrations in the rhizosphere, the high-affinity ammonium transporters (AMTs) in Arabidopsis thaliana are efficiently inactivated by phosphorylation to avoid toxic accumulation of cytoplasmic ammonium. External ammonium stimulates the phosphorylation of a conserved threonine in the cytosolic AMT1 C terminus, which allosterically inactivates AMT1 trimers. Using a genetic screen, we found that CALCINEURIN B-LIKE INTERACTING PROTEIN KINASE23 (CIPK23), a kinase that also regulates the most abundant NO3  − transporter, NPF6;3, and activates the K+ channel AKT1, inhibits ammonium transport and modulates growth sensitivity to ammonium. Loss of CIPK23 increased root NH4  + uptake after ammonium shock and conferred hypersensitivity to ammonium and to the transport analog methylammonium. CIPK23 interacts with AMT1;1 and AMT1;2 in yeast, oocytes, and in planta. Inactivation of AMT1;2 by direct interaction with CIPK23 requires kinase activity and the calcineurin B-like binding protein CBL1. Since K+, NO3  −, and NH4  + are major ions taken up by plants, CIPK23 appears to occupy a key position in controlling ion balance and ion homeostasis in the plant cell. [ABSTRACT FROM AUTHOR]

European silage maize is cultivated for animal feed and biogas production. We evaluated 210 factorial crosses of elite dent and flint lines in multilocation trials for agronomic and quality traits together with biomass and shoot concentrations of 10 elements in juvenile plants. Significant genotypic variances, mainly due to general combining ability variance of the dent lines, and high heritabilities were observed for dry matter yield (DMY) and quality traits. DMY was not correlated with quality traits, but methane fermentation yield (MFY) and metabolizable energy content (MEC) showed significant correlations with starch and fibre content. Concentrations of elements N,P,S,K were positively correlated with each other but only in few cases correlated with DMY and quality traits. Parent lines with contrasting P concentrations differed in root morphology traits. Results support DMY as primary trait for selection of silage maize hybrids, but MFY is of negligible importance in breeding for biogas contrary to MEC for animal feed. Neither biomass nor elemental composition of juvenile plants were of predictive value for final DMY or quality traits. [ABSTRACT FROM AUTHOR]