Root microbiota confers rice resistance to aluminium toxicity and phosphorus deficiency in acidic soils.

Aluminium (Al) toxicity impedes crop growth in acidic soils and is considered the second largest abiotic stress after drought for crops worldwide. Despite remarkable progress in understanding Al resistance in plants, it is still unknown whether and how the soil microbiota confers Al resistance to crops. Here we found that a synthetic community composed of highly Al-resistant bacterial strains isolated from the rice rhizosphere increased rice yield by 26.36% in acidic fields. The synthetic community harvested rhizodeposited carbon for successful proliferation and mitigated soil acidification and Al toxicity through extracellular protonation. The functional coordination between plants and microbes offers a promising way to increase the usage of legacy phosphorus in topsoil. These findings highlight the potential of microbial tools for advancing sustainable agriculture in acidic soils.

Comparative physiological and proteomic response to phosphate deficiency between two wheat genotypes differing in phosphorus utilization efficiency.

Genetic variation in phosphorus utilization efficiency (PUE) widely exists among wheat genotypes. However, the underlying mechanisms are still unclear. Two contrasting wheat genotypes, Heng4399 (H4399) and Tanmai98 (TM98), were screened out from 17 bread wheat genotypes based on shoot soluble phosphate (Pi) concentrations. The TM98 had a significantly higher PUE than the H4399, especially under Pi deficiency. The induction of genes in the PHR1-centered Pi signaling pathway was significantly higher in TM98 than in H4399. Collectively, through a label-free quantitative proteomic analysis, 2110 high-confidence proteins were identified in shoots of the two wheat genotypes. Among them, 244 and 133 proteins were differentially accumulated under Pi deficiency in H4399 and TM98, respectively. The abundance of proteins related to nitrogen and phosphorus metabolic processes, small molecule metabolic process, and carboxylic acid metabolic process weas significantly affected by Pi deficiency in the shoots of the two genotypes. The abundance of proteins in energy metabolism, especially photosynthesis, was decreased by Pi deficiency in the shoots of H4399. Inversely, the PUE-efficient genotype TM98 could maintain protein abundance in energy metabolism. Moreover, the proteins involved in pyruvate metabolism, glutathione metabolism, and sulfolipid biosynthesis were significantly accumulated in TM98, which probably contributed to its high PUE. SIGNIFICANCE: Improving the PUE of wheat is urgent and crucial for sustainable agriculture. Genetic variation among wheat genotypes provides materials for exploring the underlying mechanisms for high PUE. This study selected two wheat genotypes with contrasting PUE to reveal the differences in the physiological and proteomic responses to phosphate deficiency. The PUE-efficiency genotype TM98 greatly induced the expression of genes in the PHR1-centered Pi signaling pathway. Subsequently, the TM98 could maintain the abundance of proteins related to energy metabolism and enhance the abundance of proteins involved in pyruvate metabolism, glutathione metabolism, and sulfolipid biosynthesis to increase PUE under Pi deficiency. The differentially expressed genes or proteins between the genotypes with contrasting PUE would provide potential and basis for breeding wheat varieties with improved phosphorus use efficiency.

Differentially reset transcriptomes and genome bias response orchestrate wheat response to phosphate deficiency.

Phosphorus (P) is an essential macronutrient for all organisms. Phosphate (Pi) deficiency reduces grain yield and quality in wheat. Understanding how wheat responds to Pi deficiency at the global transcriptional level remains limited. We revisited the available RNA-seq transcriptome from Pi-starved wheat roots and shoots subjected to Pi starvation. Genome-wide transcriptome resetting was observed under Pi starvation, with a total of 917 and 2338 genes being differentially expressed in roots and shoots, respectively. Chromosomal distribution analysis of the gene triplets and differentially expressed genes (DEGs) revealed that the D genome displayed genome induction bias and, specifically, the chromosome 2D might be a key contributor to Pi-limiting triggered gene expression response. Alterations in multiple metabolic pathways pertaining to secondary metabolites, transcription factors and Pi uptake-related genes were evidenced. This study provides genomic insight and the dynamic landscape of the transcriptional changes contributing to the hexaploid wheat during Pi starvation. The outcomes of this study and the follow-up experiments have the potential to assist the development of Pi-efficient wheat cultivars.

Physiological and proteomic dissection of the rice roots in response to iron deficiency and excess.

Iron (Fe) disorder is a pivotal factor that limits rice yields in many parts of the world. Extensive research has been devoted to studying how rice molecularly copes with the stresses of Fe deficiency or excess. However, a comprehensive dissection of the whole Fe-responsive atlas at the protein level is still lacking. Here, different concentrations of Fe (0, 40, 350, and 500 µM) were supplied to rice to demonstrate its response differences to Fe deficiency and excess via physiological and proteomic analysis. Results showed that compared with the normal condition, the seedling growth and contents of Fe and manganese were significantly disturbed under either Fe stress. Proteomic analysis revealed that differentially accumulated proteins under Fe deficiency and Fe excess were commonly enriched in localization, carbon metabolism, biosynthesis of amino acids, and antioxidant system. Notably, proteins with abundance retuned by Fe starvation were individually associated with phenylpropanoid biosynthesis, cysteine and methionine metabolism, while ribosome- and endocytosis-related proteins were specifically enriched in treatment of Fe overdose of 500 µM. Moreover, several novel proteins which may play potential roles in rice Fe homeostasis were predicted. These findings expand the understanding of rice Fe nutrition mechanisms, and provide efficient guidance for genetic breeding work. SIGNIFICANCE: Both iron (Fe) deficiency and excess significantly inhibited the growth of rice seedlings. Fe deficiency and excess disturbed processes of localization and cellular oxidant detoxification, metabolisms of carbohydrates and amino acids in different ways. The Fe-deficiency and Fe-excess-responsive proteins identified by the proteome were somewhat different from the reported transcriptional profiles, providing complementary information to the transcriptomic data.

Differential Effects of Nitrogen Forms on Cell Wall Phosphorus Remobilization Are Mediated by Nitric Oxide, Pectin Content, and Phosphate Transporter Expression.

NH4 (+) is a major source of inorganic nitrogen for rice (Oryza sativa), and NH4 (+) is known to stimulate the uptake of phosphorus (P). However, it is unclear whether NH4 (+) can also stimulate P remobilization when rice is grown under P-deficient conditions. In this study, we use the two rice cultivars 'Nipponbare' and 'Kasalath' that differ in their cell wall P reutilization, to demonstrate that NH4 (+) positively regulates the pectin content and activity of pectin methylesterase in root cell walls under -P conditions, thereby remobilizing more P from the cell wall and increasing soluble P in roots and shoots. Interestingly, our results show that more NO (nitric oxide) was produced in the rice root when NH4 (+) was applied as the sole nitrogen source compared with the NO3 (-) The effect of NO on the reutilization of P from the cell walls was further demonstrated through the application of the NO donor SNP (sodium nitroprusside) and c-PTIO (NO scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide). What's more, the P-transporter gene OsPT2 is up-regulated under NH4 (+) supplementation and is therefore involved in the stimulated P remobilization. In conclusion, our data provide novel (to our knowledge) insight into the regulatory mechanism by which NH4 (+) stimulates Pi reutilization in cell walls of rice.

Form of Al changes with Al concentration in leaves of buckwheat.

Buckwheat (Fagopyrum esculentum Moench. cv. Jianxi) is known as an Al-accumulating plant. The process leading to the accumulation of Al in the leaves was investigated, focusing on the chemical form of Al using 27Al-nuclear magnetic resonance. Leaves with different Al concentrations were prepared by growing buckwheat on a very acidic soil (Andosol) amended with or without CaCO3 (1 or 3 g x kg-1 soil). When the Al concentration of the leaves was lower, only one major signal was observed at a chemical shift of 16.1 ppm, which was assigned to an Al-oxalate complex at a 1:3 ratio. However, when the Al concentration of the leaves increased to a high level (e.g. 12 g Al kg-1), an additional signal at a chemical shift of 11.2 ppm was observed. This signal was assigned to an Al-citrate complex at a 1:1 ratio. In the leaf with a high Al concentration, both Al-oxalate (1:3) and Al-citrate (1:1) were detected in marginal and middle parts, while only Al-oxalate was detected in the basal part. The oxalate concentration did not differ very much between leaves with low and high Al concentrations at the same position, while citrate concentration significantly increased with increasing Al concentration when the oxalate/Al ratio became lower than 3.0. As the Al-citrate complex has been demonstrated to be the form of transport in the xylem, the results suggest that when internal oxalate is enough to form a complex with Al at a 3:1 ratio in the leaves with a low Al concentration, Al-citrate converts to Al-oxalate. However, this conversion does not occur in the leaves with a very high Al concentration, resulting in the coexistence of both Al-oxalate and Al-citrate complexes.

Compartmentation of aluminium in leaves of an Al-accumulator, Fagopyrum esculentum Moench.

Buckwheat (Fagopyrum esculentum Moench.) is an Al-accumulating plant, but the internal mechanism(s) of detoxification of Al is not fully understood. We investigated the subcellular localization of Al in the leaves of this plant (cv. Jianxi) by directly isolating protoplasts and vacuoles. Pure protoplasts and vacuoles from the leaves of buckwheat, grown hydroponically in Al solution, were obtained based on light-microscopic observation and the activities of marker enzymes of cytosol and vacuoles. More than 80% of total Al in the leaves was present in the protoplasts, and was identified as an Al-oxalate complex (1:3 ratio) by (27)Al-nuclear magnetic resonance. Oxalate and Al in the protoplasts was localized in the vacuoles. These results suggest that internal detoxification of Al in the buckwheat leaves is achieved by both complexation with oxalate and sequestration into vacuoles.