Proteomic profile of the germinating seeds reveals enhanced seedling growth in Arabidopsis rpp1a mutant.

Ribosomal phosphoprotein P1 (RPP1) is an integral component of the P-protein stalk in the 60S subunit of eukaryotic ribosomes and is required for the efficient elongation of translation. Previously, Arabidopsis RPP1A was revealed to be involved in the regulation of seed size and seed storage protein accumulation. In this work, the seedling growth analysis shows that the knockout mutation of Arabidopsis RPP1A significantly promoted seedling growth, particularly in the shoots. The label-free quantitative proteomic analysis demonstrated that a total of 593 proteins were differentially accumulated between the germinating seeds of the wild-type Col-0 and rpp1a mutant. And these proteins were significantly enriched in the intracellular transport, nitrogen compound transport, protein transport, and organophosphate metabolic process. The abundance of proteins involved in the RNA and protein processing processes, including ncRNA processing and protein folding, were significantly increased in the rpp1a mutant. Mutation in RPP1A highlighted the effects on the ribosome, energy metabolism, and nitrogen metabolism. The abundance of enzymes involved in glycolysis and pyruvate mechanism was decreased in the germinating seeds of the rpp1a mutant. Whereas the processes of amino acid biosynthesis, protein processing in endoplasmic reticulum, and biosynthesis of cofactors were enhanced in the germinating seeds of the rpp1a mutant. Taken together, the lack of RPP1A triggered changes in other ribosomal proteins, and the higher amino acid contents in the seedlings of the rpp1a mutant probably contributed to enhanced biosynthesis, processing, and transport of proteins, resulting in accelerated growth. Our results show the novel role of a P-protein and shed new light on the regulatory mechanism of seedling growth.

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.

IMA peptides function in iron homeostasis and cadmium resistance.

Iron (Fe), an essential micronutrient, participates in photosynthesis, respiration, and many other enzymatic reactions. Cadmium (Cd), by contrast, is a toxic element to virtually all living organisms. Both Fe deficiency and Cd toxicity severally impair crop growth and productivity, finally leading to human health issues. Understanding how plants control the uptake and homeostasis of Fe and combat Cd toxicity thus is mandatory to develop Fe-enriched but Cd-cleaned germplasms for human beings. Recent studies in Arabidopsis and rice have revealed that IRON MAN (IMA) peptides stand out as a key regulator to respond to Fe deficiency by competitively interacting with a ubiquitin E3 ligase, thus inhibiting the degradation of IVc subgroup bHLH transcription factors (TFs), mediated by 26 S proteasome. Elevated expression of IMA confers tolerance to Cd stress in both Arabidopsis and wheat by activating the iron deficiency response. Here, we discuss recent breakthroughs that IMA peptides function in the Fe-deficiency response to attain Fe homeostasis and combat Cd toxicity as a potential candidate for phytoremediation.

Label-Free Quantitative Proteomics in Plant.

Label-free quantitation (LFQ) proteomics, mainly based on the extraction of the peptide (precursor) intensity at the MS1 (mass spectrum 1) level, enables to quantify the relative amount of the proteins among samples. In an LFQ proteomics study, all samples are scanned individually on an advanced mass spectrometer and the chromatographic features of each run are extracted to generate consensus patterns among various runs in the experiment. Here, we describe the LFQ proteomics experimental protocol adapted for plant research, such as plant iron homeostasis.

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.

Impacts of iron on phosphate starvation-induced root hair growth in Arabidopsis.

In Arabidopsis, phosphate starvation (-Pi)-induced responses of primary root and lateral root growth are documented to be correlated with ambient iron (Fe) status. However, whether and how Fe participates in -Pi-induced root hair growth (RHG) remains unclear. Here, responses of RHG to different Fe concentrations under Pi sufficiency/deficiency were verified. Generally, distinct dosage effects of Fe on RHG appeared at both Pi levels, due to the generation of reactive oxygen species. Following analyses using auxin mutants and the phr1 mutant revealed that auxin and the central regulator PHR1 are required for Fe-triggered RHG under -Pi. A further proteomic study indicated that processes of vesicle trafficking and auxin synthesis and transport were affected by Fe under -Pi, which were subsequently validated by using a vesicle trafficking inhibitor, brefeldin A, and an auxin reporter, R2D2. Moreover, vesicle trafficking-mediated recycling of PIN2, an auxin efflux transporter, was notably affected by Fe under -Pi. Correspondingly, root hairs of pin2 mutant displayed attenuated responses to Fe under -Pi. Together, we propose that Fe affects auxin signalling probably by modulating vesicle trafficking, chiefly the PIN2 recycling, which might work jointly with PHR1 on modulating -Pi-induced RHG.

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.

Exogenous abscisic acid alleviates Cd toxicity in Arabidopsis thaliana by inhibiting Cd uptake, translocation and accumulation, and promoting Cd chelation and efflux.

Exogenous abscisic acid (ABA) has been implicated in plant response to cadmium (Cd) stress, but the underlying mechanism remains unclear. In the present study, we found that exogenous ABA application decreased Cd fixation in wild type (WT) root cell wall through reducing the hemicelluloses content, in parallel with the decreased expression of IRT1, ZIP1, ZIP4, HMA2 and HMA4, which are related to Cd uptake and translocation, and the increased expression of PDF2.6, PDR8 and AIT1, which are related to Cd chelation, efflux, and accumulation inhibition. These changes might be associated with the reduced Cd accumulation in roots and shoots and the alleviated Cd toxicity. In contrast, the mutation of ABI4, a transcription factor in ABA signaling pathway, significantly increased the expression of IRT1, ZIP1, ZIP4, HMA2 and HMA4, while decreased the expression of AIT1, PDF2.6 and PDR8, enhancing Cd accumulation in roots and shoots of abi4. The enhanced Cd-sensitivity in abi4 mutant could not be rescued by exogenous ABA addition compared with WT. In a word, we conclude that exogenous ABA mitigates Cd toxicity in Arabidopsis thaliana via inhibiting Cd uptake, translocation and accumulation, promoting Cd chelation and efflux, a pathway that might be regulated by ABI4.

Salicylic Acid Acts Upstream of Auxin and Nitric Oxide (NO) in Cell Wall Phosphorus Remobilization in Phosphorus Deficient Rice.

Salicylic acid (SA) is thought to be involved in phosphorus (P) stress response in plants, but the underlying molecular mechanisms are poorly understood. Here, we showed that P deficiency significantly increased the endogenous SA content by inducing the SA synthesis pathway, especially for up-regulating the expression of PAL3. Furthermore, rice SA synthetic mutants pal3 exhibited the decreased root and shoot soluble P content, indicating that SA is involved in P homeostasis in plants. Subsequently, application of exogenous SA could increase the root and shoot soluble P content through regulating the root and shoot cell wall P reutilization. In addition, - P + SA treatment highly upregulated the expression of P transporters such as OsPT2 and OsPT6, together with the increased xylem P content, suggesting that SA also participates in the translocation of the P from the root to the shoot. Moreover, both signal molecular nitric oxide (NO) and auxin (IAA) production were enhanced when SA is applied while the addition of respective inhibitor c-PTIO (NO scavenger) and NPA (IAA transport inhibitor) significantly decreased the root and shoot cell wall P remobilization in response to P starvation. Taken together, here SA-IAA-NO-cell wall P reutilization pathway has been discovered in P-starved rice.

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.

The Role of Nitric Oxide Signaling in Plant Responses to Cadmium Stress.

Nitric oxide (NO) is a widely distributed gaseous signaling molecule in plants that can be synthesized through enzymatic and non-enzymatic pathways and plays an important role in plant growth and development, signal transduction, and response to biotic and abiotic stresses. Cadmium (Cd) is a heavy metal pollutant widely found in the environment, which not only inhibits plant growth but also enters humans through the food chain and endangers human health. To reduce or avoid the adverse effects of Cd stress, plants have evolved a range of coping mechanisms. Many studies have shown that NO is also involved in the plant response to Cd stress and plays an important role in regulating the resistance of plants to Cd stress. However, until now, the mechanisms by which Cd stress regulates the level of endogenous NO accumulation in plant cells remained unclear, and the role of exogenous NO in plant responses to Cd stress is controversial. This review describes the pathways of NO production in plants, the changes in endogenous NO levels in plants under Cd stress, and the effects of exogenous NO on regulating plant resistance to Cd stress.

A proteomic analysis of Arabidopsis ribosomal phosphoprotein P1A mutant.

Ribosomal proteins are involved in the regulation of plant growth and development. However, the regulatory processes of most ribosomal proteins remain unclear. In this study, Arabidopsis plants with the mutation in ribosomal phosphoprotein P1A (RPP1A) produce larger and heavier seeds than wild-type plants. A comparative quantitative label-free proteomic analysis revealed that a total of 215 proteins were differentially accumulated between the young siliques of the wild type and rpp1a mutant. Knockout of RPP1A significantly reduced the abundance of proteins involved in carboxylic acid metabolism and lipid biosynthesis. Consistent with this, a metabolic analysis showed that the organic acids in the tricarboxylic acid cycle and the carbohydrates in the pentose phosphate pathway were severely reduced in the mature rpp1a mutant seeds. In contrast, the abundance of proteins related to seed maturation, especially seed storage proteins, was markedly increased during seed development. Indeed, seed storage proteins were accumulated in the mature rpp1a mutant seeds, and the seed nitrogen and sulfur contents were also increased. These results indicate that more carbon intermediates probably enter the nitrogen flow for the enhanced synthesis of seed storage proteins, which might subsequently contribute to the enlarged seed size in the rpp1a mutant. SIGNIFICANCE: Ribosomes are responsible for protein synthesis and are generally perceived as the housekeeping components in the cells. In this study, the knockout of RPP1A leads to an increased seed size through repressing carbon metabolism and lipid biosynthesis, and increasing the synthesis of seed storage proteins. Meanwhile, the abundance of seed storage proteins and the nitrogen and sulfur concentrations were increased in the mature rpp1a mutant seeds. The results provide a novel insight into the genetic regulatory networks for the control of seed size and seed storage protein accumulation, and this knowledge may facilitate the improvement of crop seed size.

Ectopic expression of IMA small peptide genes confers tolerance to cadmium stress in Arabidopsis through activating the iron deficiency response.

Increasing cadmium (Cd) pollution severely affects plant growth and development, posing risks to human health via food chains. The Cd toxicity could be mitigated by improving Fe nutrient in plants. IMA1 and IMA3, two novel small peptides functionally epistatic to the key transcription factor bHLH39 but independent of bHLH104, were recently identified as the newest additions to the Fe regulatory cascade, but their roles in Cd uptake and toxicity remain not addressed. Here, the functions of two IMAs and two transcription factors related to Cd tolerance were verified. Overexpression of either bHLH39 or bHLH104 in Arabidopsis showed weak roles in Cd tolerance, but overexpression of IMAs, which activates the Fe-deficient response, significantly enhanced Cd tolerance, showing greater root elongation, biomass and chlorophyll contents. The Cd contents did not show significant difference among the overexpression lines. Further investigations revealed that the tolerance of transgenic plants to Cd mainly depended on higher Fe accumulation, which decreased the MDA contents and enhanced root elongation under Cd exposure, finally contributing to attenuating Cd toxicity. Taken together, the results suggest that increasing Fe accumulation is promising for improving plant tolerance to Cd toxicity and that IMAs are potential candidates for solving Cd toxicity problem.

PERK13 modulates phosphate deficiency-induced root hair elongation in Arabidopsis.

Phosphate starvation (-Pi)-induced root hair is crucial for enhancing plants' Pi absorption. Proline-rich extensin-like receptor kinase 13 (PERK13) is transcriptionally induced by -Pi and co-expressed with genes associated with root hair growth. However, how PERK13 participates in -Pi-induced root hair growth remains unclear. Here, we found that PERK13 was transcriptionally responsive to Pi, nitrogen, and iron deficiencies. Loss of PERK13 function (perk13) enhanced root hair growth under Pi/nitrogen limitation. Similar phenotype was also observed in transgenic lines overexpressing PERK13 (PERK13ox). Under -Pi, both perk13 and PERK13ox showed prolonged root hair elongation and increased reactive oxygen species (ROS). Deletion analysis showed, in PERK13ox, the extracellular domain was indispensable for PERK13 in -Pi-induced root hair growth. Different transcription profiles were observed under -Pi between perk13 and PERK13ox with the jasmonate zim-domain genes being repressed in perk13 and genes involved in cell wall remodeling being increased in PERK13ox. Taken together, we demonstrated that PERK13 participates in -Pi-induced root hair growth probably via regulating root hair elongation and the generation of ROS. Our study also suggested PERK13 probably being a vital hub coupling the environmental cues and root hair growth, and might play dual roles in -Pi-induced root hair growth via different processes.

Greater morphological and primary metabolic adaptations in roots contribute to phosphate-deficiency tolerance in the bread wheat cultivar Kenong199.

BACKGROUND: Phosphate (Pi) deficiency severely affects crop growth and productivity, including wheat, therefore it is necessary to develop cultivars with enhanced Pi-deficiency tolerance. However, the underlying mechanism of Pi-deficiency tolerance in wheat is still elusive. Two contrasting wheat cultivars, low-Pi tolerant Kenong199 (KN199) and low-Pi sensitive Chinese Spring (CS) were used to reveal adaptations in response to Pi deficiency at the morphological, physiological, metabolic, and molecular levels. RESULTS: KN199 was more tolerant to Pi deficiency than CS with significantly increased root biomass and R/S ratio. Root traits, the total root length, total root surface area, and total root volume, were remarkably enhanced by Pi deficiency in KN199. The shoot total P and soluble Pi concentrations of KN199 were significantly higher than those of CS, but not in roots. In KN199, high Pi level in shoots is a higher priority than that in roots under Pi deficiency. It was probably due to differentially regulation in the miR399-mediated signaling network between the shoots of the two cultivars. The Pi deficiency-induced root architecture adaptation in KN199 was attributed to the regulation of the hormone-mediated signaling (ethylene, gibberellin, and jasmonates). The expression of genes associated with root development and Pi uptake was enhanced in KN199. Some primary metabolites (amino acids and organic acids) were significantly accumulated in roots of KN199 under Pi deficiency. CONCLUSIONS: The low-Pi tolerant wheat cultivar KN199 possessed greater morphological and primary metabolic adaptations in roots than CS under Pi deficiency. The adaption and the underlying molecular mechanisms in wheat provide a better understanding of the Pi-deficiency tolerance and the strategies for improving Pi efficiency in wheat.

Comparative proteomics reveals new insights into the endosperm responses to drought, salinity and submergence in germinating wheat seeds.

KEY MESSAGE: Beyond the role of a nutrient reservoir during germination, the endosperm of wheat seeds also responds to different abiotic stresses via modification of the protein profiles. The endosperm is the main component of wheat seeds. During seed germination, it provides nutrients to support the embryo development, and its constituents vary under environmental stresses such as drought, salinity and submergence that are associated with disordered water supply. However, the molecular mechanism of these stress responses remains unclear. In this study, a comparative label-free proteomic analysis was performed on endosperm from the germinating wheat seeds subjected to PEG, NaCl and submergence treatments. In total, 2273 high confidence proteins were detected, and 234, 207 and 209 of them were identified as differentially expressed proteins (DEPs) under the three stresses, respectively. Functional classification revealed that the DEPs were mainly involved in protein, amino acid and organic acid metabolic process in all stress treatments. While some other metabolic processes were highlighted in one or two of the stresses specifically, such as oxidative phosphorylation in PEG and submergence, and ß-alanine metabolism in PEG and NaCl treatments. The identification of a series of stress-related proteins and their biased expression in different stresses indicates the active stress-responding role of endosperm beyond a simple nutrient reservoir during germination, while the overall stress responses of the endosperm were found to be moderate and lag behind the embryo. Besides, some fundamental processes and DEPs shared by the three stresses could be selected priorly for future molecular breeding researches. Our results provide new insights into the mechanism of endosperm responses to abiotic stresses during seed germination.

Proteomic dissection of the similar and different responses of wheat to drought, salinity and submergence during seed germination.

Wheat (Triticum aestivum L.) is one of the major crops worldwide and its production is inevitably subjected to various biotic/abiotic stresses during the life cycle. Drought, salinity and flooding are among the most severe abiotic stresses restricting wheat yields and could occur at very early stages such as seed germination. How wheat seed germination responds to these different stresses remains incomplete. To fill the information gap, a label-free proteomic analysis was applied to decipher the proteomic profiling of the germinating wheat seeds subjected to PEG, NaCl and submergence treatments. In total, 4295 proteins were detected, of which 465, 397 and 732 showed significant alterations in abundance under those stresses when compared with control. A common denominator found in the response observed to all three stresses are changes related to small molecule metabolic processes, and particularly in pathways associated with phenylpropanoid biosynthesis and fatty acid degradation. It was also noticeable that pathways like cysteine and methionine metabolism in the PEG or submergence treatment and starch and sucrose metabolism in the submergence treatment are specifically pronounced. Functional analysis of putative proteins participating in these pathways revealed distinct responsive patterns across different stresses. SIGNIFICANCE: Wheat (Triticum aestivum L.) is one of the most important staple crops in the world, but its growth and productivity are frequently restrained by stresses such as drought, salinity and flooding. To date, many resources have been documented to investigate how wheat responds and adapts to these individual stresses during plant development and yield formation, but little attention was paid to the understandings of the internal link between different conditions, especially during the germination process, a critical stage that determines the optimal growth of wheat. In this study, we carried out the proteome profiling of the germinating seeds of a common wheat cultivar, Chinese Spring, subjected to PEG, NaCl and submergence stresses. We found that the phenylpropanoid biosynthesis and fatty acid degradation pathways were enriched as the ubiquitous stress responses, while some pathways were stress-specific, for instance, starch and sucrose metabolism against submergence. The changes in some of the altered processes were further validated by physiological and molecular approaches. Our results suggest that the overall pathway profiles concerned with the three stresses were similar, but the specific procedures and components in each process varied greatly. The altered proteins and processes can be taken as effective candidates in future breeding and agronomic modification researches.

Physiological and Proteomic Dissection of the Responses of Two Contrasting Wheat Genotypes to Nitrogen Deficiency.

Nitrogen deficiency usually occurs along with aluminum toxicity in acidic soil, which is one of the major constraints for wheat production worldwide. In order to compare adaptive processes to N deficiency with different Al-tolerant wheat cultivars, we chose Atlas 66 and Scout 66 to comprehensively analyze the physiological responses to N deficiency, coupled with label-free mass spectrometry-based proteomics analysis. Results showed that both cultivars were comparable in most physiological indexes under N deficient conditions. However, the chlorophyll content in Scout 66 was higher than that of Atlas 66 under N deficiency. Further proteomic analysis identified 5592 and 5496 proteins in the leaves of Atlas 66 and Scout 66, respectively, of which 658 and 734 proteins were shown to significantly change in abundance upon N deficiency, respectively. The majority of the differentially expressed proteins were involved in cellular N compound metabolic process, photosynthesis, etc. Moreover, tetrapyrrole synthesis and sulfate assimilation were particularly enriched in Scout 66. Our findings provide evidence towards a better understanding of genotype-dependent responses under N deficiency which could help us to develop N efficient cultivars to various soil types.

Can Aluminum Tolerant Wheat Cultivar Perform Better under Phosphate Deficient Conditions?

Low availability of inorganic phosphate (Pi), together with aluminum (Al), is a major constraint for plant growth and development in acidic soils. To investigate whether or not Al-resistant cultivars can perform better under Pi deficiency, we chose two wheat cultivars with different Al-responses-Atlas 66, being Al-tolerant, and Scout 66, which is Al-sensitive-and analyzed their responses to Pi deficiency. Results showed that, unexpectedly, the Al-sensitive cultivar Scout 66 contained comparatively higher amount of soluble phosphate (Pi) and total phosphorus (P) both in the roots and in the shoots than Atlas 66 under P deficiency. In addition, Scout 66 exhibited higher root biomass, root volume, and root tip numbers, compared with Atlas 66. The expression of Pi-responsive marker genes, TaIPS1, TaSPX3, and TaSQD2 was strongly induced in both cultivars, but the extents of induction were higher in Scout 66 than in Atlas 66 under long-term Pi starvation. Taken together, our results suggest that the Al-sensitive cultivar Scout 66 performed much better under sole Pi starvation, which sets the following experimental stage to uncover the underlying mechanisms of why Scout 66 can display better under Pi deficiency. Our study also raises an open question whether Al-resistant plants are more sensitive to Pi deficiency.

Boron Alleviates Aluminum Toxicity by Promoting Root Alkalization in Transition Zone via Polar Auxin Transport.

Boron (B) alleviates aluminum (Al) toxicity in higher plants; however, the underlying mechanisms behind this phenomenon remain unknown. Here, we used bromocresol green pH indicator, noninvasive microtest, and microelectrode ion flux estimation techniques to demonstrate that B promotes root surface pH gradients in pea (Pisum sativum) roots, leading to alkalization in the root transition zone and acidification in the elongation zone, while Al inhibits these pH gradients. B significantly decreased Al accumulation in the transition zone (∼1.0-2.5 mm from the apex) of lateral roots, thereby alleviating Al-induced inhibition of root elongation. Net indole acetic acid (IAA) efflux detected by an IAA-sensitive platinum microelectrode showed that polar auxin transport, which peaked in the root transition zone, was inhibited by Al toxicity, while it was partially recovered by B. Electrophysiological experiments using the Arabidopsis (Arabidopsis thaliana) auxin transporter mutants (auxin resistant1-7; pin-formed2 [pin2]) and the specific polar auxin transporter inhibitor1-naphthylphthalamic acid showed that PIN2-based polar auxin transport is involved in root surface alkalization in the transition zone. Our results suggest that B promotes polar auxin transport driven by the auxin efflux transporter PIN2 and leads to the downstream regulation of the plasma membrane-H+-ATPase, resulting in elevated root surface pH, which is essential to decrease Al accumulation in this Al-targeted apical root zone. These findings provide a mechanistic explanation for the role of exogenous B in alleviation of Al accumulation and toxicity in plants.