The high-affinity transporter BnPHT1;4 is involved in phosphorus acquisition and mobilization for facilitating seed germination and early seedling growth of Brassica napus

An alfalfa MYB-like transcriptional factor MsMYBH positively regulates alfalfa seedling drought resistance and undergoes MsWAV3-mediated degradation

Drought is a major threat to alfalfa (Medicago sativa L.) production. The discovery of important alfalfa genes regulating drought response will facilitate breeding for drought-resistant alfalfa cultivars. Here, we report a genome-wide association study of drought resistance in alfalfa. We identified and functionally characterized an MYB-like transcription factor gene (MsMYBH), which increases the drought resistance in alfalfa. Compared with the wild-types, the biomass and forage quality were enhanced in MsMYBH overexpressed plants. Combined RNA-seq, proteomics and chromatin immunoprecipitation analysis showed that MsMYBH can directly bind to the promoters of MsMCP1, MsMCP2, MsPRX1A and MsCARCAB to improve their expression. The outcomes of such interactions include better water balance, high photosynthetic efficiency and scavenge excess H2O2 in response to drought. Furthermore, an E3 ubiquitin ligase (MsWAV3) was found to induce MsMYBH degradation under long-term drought, via the 26S proteasome pathway. Furthermore, variable-number tandem repeats in MsMYBH promoter were characterized among a collection of germplasms, and the variation is associated with promoter activity. Collectively, our findings shed light on the functions of MsMYBH and provide a pivotal gene that could be leveraged for breeding drought-resistant alfalfa. This discovery also offers new insights into the mechanisms of drought resistance in alfalfa.

Ethanol suppresses rice seed germination through inhibiting ROS signaling

Ethanol is frequently used not only as priming but also as a solvent to dissolve hardly water-soluble phytohormones gibberellic acid (GA3) and abscisic acid (ABA) in seed germination. However, the molecular and physiological mechanisms of ethanol's impact on seed germination remain elusive. In this report, we investigated how ethanol affected reactive oxygen species (ROS) during rice seed germination. Ethanol at a concentration of 3.5% (v/v) inhibited 90% seed germination, which was almost reversed by H2O2. H2O2 contents in embryos were reduced by ethanol after 18 h imbibition. Antioxidant enzymes assays revealed that only superoxide dismutase (SOD) activities in seed embryos were lowered by ethanol, in line with the suppressed mRNA expression of SOD genes during imbibition. Additionally, compared to the mock condition, ethanol increased ABA contents but decreased GA (GA1 and GA3) in seed embryos, resulting in disharmonizing GA/ABA balance. Conceivably ethanol induced transcription of OsNCEDs, the key genes for ABA biosynthesis, and OsABA8ox3, a key gene for ABA catabolism. Furthermore, ethanol promoted ABA signaling by upregulating ABA receptor genes and ABA-responsive element (ABRE)-binding protein/ABRE-binding factors during imbibition. Overall, our results demonstrate that lowering of H2O2 levels due to suppressed SOD activities in rice germinating seed embryos is the decisive factor for ethanol-induced inhibition of seed germination, and GA/ABA balance and ABA signaling also play important roles in ethanol's inhibitory impact on seed germination.

Phosphate Transporter BnaPT37 Regulates Phosphate Homeostasis in Brassica napus by Changing Its Translocation and Distribution In Vivo

Inorganic phosphate (Pi) is actively taken up by Pi transporters (PTs) from the soil and transported into the plant. Here, we functionally characterized the Brassica napus gene BnaPT37, which belongs to the PHT1 family. BnaPT37 is a plasma membrane-localized protein containing 534 amino acids. Expression of BnaPT37 increased significantly under Pi deficiency in various tissues, especially in fully expanded leaves. Expression of the β-glucuronidase reporter gene driven by the BnaPT37 promoter showed that BnaPT37 is expressed in the root, stem, calyx, and leaf under Pi deficiency. BnaPT37 can complement a yeast mutant strain defective in five Pi transporters and can restore the growth of the Arabidopsis atpt1/2 double mutant under Pi deprivation. Overexpression of BnaPT37 in rapeseed significantly increased Pi translocation from root to shoot. Moreover, the movement of Pi from fully expanded leaves to new leaves and roots was enhanced in the transgenic lines compared to the wild type. However, the overexpression of BnaPT37 inhibited the flowering time, plant height, and Pi accumulation in seeds. In conclusion, BnaPT37 functions as a plasma membrane-localized Pi transporter and might be involved in Pi translocation from root to shoot and Pi distribution from source to sink in B. napus.

Analysis of Hormone Regulation on Seed Germination of Coix Based on Muli-Omics Analysis

Seed germination is an important stage of growth and reproduction and plays an important role in the life cycle of spermatophyte. It is co-determined by both genetic and environmental factors, and plant hormone regulation may be a highly conservative mechanism. Coix lachryrma-jobi (coix) is a grain with balanced nutrition for medicine and food and has substantial production value. It is an important part of agricultural production, and the efficiency of seed germination after sowing is a key link. In this study, coix species "small white shell Xingren" was used as the experimental material, and changes in gene expression levels and metabolite enrichment in seeds were identified by transcriptome and metabonomic analysis before and after seed germination. A total of 599 metabolites, including those from amino acid metabolism, sugar metabolism, and fatty acid metabolism, were significantly increased in germinating coix. Simultaneously, 10,929 differentially expressed genes (DEGs) were identified, and functional clusters of genes were also significantly clustered in hormone-signaling and glucose and fatty acid metabolism. In addition, this study found that a considerable number of hormone-signaling genes were significantly up-regulated during seed germination, activating multiple metabolic processes. The results of our conjoint analysis of multi omics showed that glucose and fatty acid metabolism played an important role in seed germination under hormone regulation.

Revealing the effect of seed phosphorus concentration on seedling vigour and growth of rice using mutagenesis approach

The harvested plant products, specifically, the grains of cereals are major drivers of soil phosphorus (P) depletion. However, the breeding or biotechnology efforts to develop low P seeds have not been attempted because of possible adverse effects on seedling vigour and crop establishment. Several studies have contradictory observations on influence of seed P on seedling vigour. Lack of appropriate genetic material has been the major bottleneck in reaching the consensus. In this study, we used 30 EMS induced mutants of rice cultivar Nagina22 to understand the role of seed P on seedling vigour and associated physiological processes. Seedling vigour, morpho-physiological characteristics, acid phosphatases, alpha-amylase, and expression of P transporter genes were analyzed in seedlings obtained from seeds of high and low grain P mutants. The study suggests that seed P has a significant role on seedling vigour, chlorophyll content and photosynthesis process of young seedlings, and P transport from roots. Notably, we identified few mutants such as NH4791, NH4785, NH4714, NH4663, NH4614, and NH4618 which showed least influence of low seed P on seedling vigour and other metabolic processes. Therefore, these mutants can be used in breeding programs aiming for development of low P grains. Also, these and other identified mutants can be used to decipher the genetic and molecular mechanisms regulating the differential response of seed P on germination, seedling vigour and several other physiological processes influencing the crop growth and establishment.

The Role of Membrane Transporters in Plant Growth and Development, and Abiotic Stress Tolerance

The proteins of membrane transporters (MTs) are embedded within membrane-bounded organelles and are the prime targets for improvements in the efficiency of water and nutrient transportation. Their function is to maintain cellular homeostasis by controlling ionic movements across cellular channels from roots to upper plant parts, xylem loading and remobilization of sugar molecules from photosynthesis tissues in the leaf (source) to roots, stem and seeds (sink) via phloem loading. The plant's entire source-to-sink relationship is regulated by multiple transporting proteins in a highly sophisticated manner and driven based on different stages of plant growth and development (PG&D) and environmental changes. The MTs play a pivotal role in PG&D in terms of increased plant height, branches/tiller numbers, enhanced numbers, length and filled panicles per plant, seed yield and grain quality. Dynamic climatic changes disturbed ionic balance (salt, drought and heavy metals) and sugar supply (cold and heat stress) in plants. Due to poor selectivity, some of the MTs also uptake toxic elements in roots negatively impact PG&D and are later on also exported to upper parts where they deteriorate grain quality. As an adaptive strategy, in response to salt and heavy metals, plants activate plasma membranes and vacuolar membrane-localized MTs that export toxic elements into vacuole and also translocate in the root's tips and shoot. However, in case of drought, cold and heat stresses, MTs increased water and sugar supplies to all organs. In this review, we mainly review recent literature from Arabidopsis, halophytes and major field crops such as rice, wheat, maize and oilseed rape in order to argue the global role of MTs in PG&D, and abiotic stress tolerance. We also discussed gene expression level changes and genomic variations within a species as well as within a family in response to developmental and environmental cues.

Genome-wide association study dissects the genetic control of plant height and branch number in response to low-phosphorus stress in Brassica napus

BACKGROUND AND AIMS

Oilseed rape (Brassica napus) is one of the most important oil crops worldwide. Phosphorus (P) deficiency severely decreases the plant height and branch number of B. napus. However, the genetic bases controlling plant height and branch number in B. napus under P deficiency remain largely unknown. This study aims to mine candidate genes for plant height and branch number by genome-wide association study (GWAS) and determine low-P-tolerance haplotypes.

METHODS

An association panel of B. napus was grown in the field with a low P supply (P, 0 kg ha-1) and a sufficient P supply (P, 40 kg ha-1) across 2 years and plant height and branch number were investigated. More than five million single-nucleotide polymorphisms (SNPs) were used to conduct GWAS of plant height and branch number at two contrasting P supplies.

KEY RESULTS

A total of 2127 SNPs were strongly associated (P < 6·25 × 10-07) with plant height and branch number at two P supplies. There was significant correlation between phenotypic variation and the number of favourable alleles of associated loci on chromosomes A10 (chrA10_821671) and C08 (chrC08_27999846), which will contribute to breeding improvement by aggregating these SNPs. BnaA10g09290D and BnaC08g26640D were identified to be associated with chrA10_821671 and chrC08_27999846, respectively. Candidate gene association analysis and haplotype analysis showed that the inbred lines carrying ATT at BnaA10g09290Hap1 and AAT at BnaC08g26640Hap1 had greater plant height than lines carrying other haplotype alleles at low P supply.

CONCLUSION

Our results demonstrate the power of GWAS in identifying genes of interest in B. napus and provided insights into the genetic basis of plant height and branch number at low P supply in B. napus. Candidate genes and favourable haplotypes may facilitate marker-based breeding efforts aimed at improving P use efficiency in B. napus.

Fatty acid export protein BnFAX6 functions in lipid synthesis and axillary bud growth in Brassica napus

Sugar is considered as the primary regulator of plant apical dominance, whereby the outgrowth of axillary buds is inhibited by the shoot tip. However, there are some deficiencies in this theory. Here, we reveal that Fatty Acid Export 6 (BnFAX6) functions in FA transport, and linoleic acid or its derivatives acts as a signaling molecule in regulating apical dominance of Brassica napus. BnFAX6 is responsible for mediating FA export from plastids. Overexpression of BnFAX6 in B. napus heightened the expression of genes involved in glycolysis and lipid biosynthesis, promoting the flow of photosynthetic products to the biosynthesis of FAs (including linoleic acid and its derivatives). Enhancing expression of BnFAX6 increased oil content in seeds and leaves and resulted in semi-dwarf and increased branching phenotypes with more siliques, contributing to increased yield per plant relative to wild-type. Furthermore, decapitation led to the rapid flow of the carbon from photosynthetic products to FA biosynthesis in axillary buds, consistent with the overexpression of BnFAX6 in B. napus. In addition, free FAs, especially linoleic acid, were rapidly transported from leaves to axillary buds. Increasing linoleic acid in axillary buds repressed expression of a key transcriptional regulator responsible for maintaining bud dormancy, resulting in bud outgrowth. Taken together, we uncovered that BnFAX6 mediating FA export from plastids functions in lipid biosynthesis and in axillary bud dormancy release, possibly through enhancing linoleic acid level in axillary buds of B. napus.

Boron and Phosphorus Act Synergistically to Modulate Absorption and Distribution of Phosphorus and Growth of Brassica napus

Rapeseed (Brassica napus L.) is highly susceptible to boron (B) and phosphorus (P) deficiencies, yet knowledge of how these two essential elements interact to contribute to plant growth and crop yield is limited. To this end, a pot experiment with three P application rates (5, 75, and 150 mg P₂O₅ kg^-1 dry soil) and two B application rates (0.25 and 1 mg B kg^-1 dry soil) was conducted. The results showed that high P combined with high B optimized plant growth and facilitated P distribution forward to seeds compared with high P and low B combination at the maturity stage. Under low P conditions, low B supply was more beneficial for P absorption at seedling and bolting stages and increased P distribution ratio in seeds at the maturity stage, resulting in higher photosynthetic efficiency and growth parameters than low P and high B combination. Interestingly, high B supply could upregulate the expression of the P-starvation-induced gene BnaC3.SPX3 and P transport genes in roots under low P conditions, so low B-facilitated P absorption appears to be a BnaPHT1s-independent process. Significant differences of B and P interaction on the seed yield, net photosynthetic rate, and total P absorption and distribution at the maturity stage between two cultivars might reflect the distinct genotypic properties. Overall, our findings highlight the importance of balanced B and P nutrition which acts synergistically to modulate growth and yield formation of B. napus either in nutrition deficiency or sufficiency.

Genome-Wide Analysis of Phosphorus Transporter Genes in Brassica and Their Roles in Heavy Metal Stress Tolerance

Phosphorus transporter (PHT) genes encode H2PO4-/H+ co-transporters that absorb and transport inorganic nutrient elements required for plant development and growth and protect plants from heavy metal stress. However, little is known about the roles of PHTs in Brassica compared to Arabidopsis thaliana. In this study, we identified and extensively analyzed 336 PHTs from three diploid (B. rapa, B. oleracea, and B. nigra) and two allotetraploid (B. juncea and B. napus) Brassica species. We categorized the PHTs into five phylogenetic clusters (PHT1-PHT5), including 201 PHT1 homologs, 15 PHT2 homologs, 40 PHT3 homologs, 54 PHT4 homologs, and 26 PHT5 homologs, which are unevenly distributed on the corresponding chromosomes of the five Brassica species. All PHT family genes from Brassica are more closely related to Arabidopsis PHTs in the same vs. other clusters, suggesting they are highly conserved and have similar functions. Duplication and synteny analysis revealed that segmental and tandem duplications led to the expansion of the PHT gene family during the process of polyploidization and that members of this family have undergone purifying selection during evolution based on Ka/Ks values. Finally, we explored the expression profiles of BnaPHT family genes in specific tissues, at various developmental stages, and under heavy metal stress via RNA-seq analysis and qRT-PCR. BnaPHTs that were induced by heavy metal treatment might mediate the response of rapeseed to this important stress. This study represents the first genome-wide analysis of PHT family genes in Brassica species. Our findings improve our understanding of PHT family genes and provide a basis for further studies of BnaPHTs in plant tolerance to heavy metal stress.

Phosphate transporters, PnPht1;1 and PnPht1;2 from Panax notoginseng enhance phosphate and arsenate acquisition

BACKGROUND

Panax notoginseng is a medicinally important Chinese herb with a long history of cultivation and clinical application. The planting area is mainly distributed in Wenshan Prefecture, where the quality and safety of P. notoginseng have been threatened by high concentration of arsenic (As) from the soil. The roles of phosphate (Pi) transporters involved in Pi acquisition and arsenate (AsV) tolerance were still unclear in this species.

RESULTS

In this study, two open reading frames (ORFs) of PnPht1;1 and PnPht1;2 separated from P. notoginseng were cloned based on RNA-seq, which encoded 527 and 541 amino acids, respectively. The results of relative expression levels showed that both genes responded to the Pi deficiency or As exposure, and were highly upregulated. Heterologous expression in Saccharomyces cerevisiae MB192 revealed that PnPht1;1 and PnPht1;2 performed optimally in complementing the yeast Pi-transport defect, particularly in PnPht1;2. Cells expressing PnPht1;2 had a stronger AsV tolerance than PnPht1;1-expressing cells, and accumulated less As in cells under a high-Pi concentration. Combining with the result of plasma membrane localization, these data confirmed that transporters PnPht1;1 and PnPht1;2 were putative high-affinity H+/H2PO4- symporters, mediating the uptake of Pi and AsV.

CONCLUSION

PnPht1;1 and PnPht1;2 encoded functional plasma membrane-localized transporter proteins that mediated a putative high-affinity Pi/H+ symport activity. Expression of PnPht1;1 or PnPht1;2 in mutant strains could enhance the uptake of Pi and AsV, that is probably responsible for the As accumulation in the roots of P. notoginseng.

Molecular identification of the phosphate transporter family 1 (PHT1) genes and their expression profiles in response to phosphorus deprivation and other abiotic stresses in Brassica napus

Phosphate (Pi) transporters play critical roles in Pi acquisition and homeostasis. However, little is known about these transporters in oilseed rape. Therefore, the aim of the present study was to characterize the members of the PHT1 gene family in allotetraploid Brassica napus and to analyze their expression profiles in response to environmental stresses. In total, 49 PHT1 family members were identified in B. napus, including 27 genes in the A subgenome and 22 in the C subgenome. Most of the PHT1 proteins were predicted to localize to the plasma membrane. Phylogenetic analysis suggested that the members of the PHT1 gene family can be divided into seven clades, with the introns/exons and protein motifs conserved in each clade. Collinearity analysis revealed that most of the BnaPHT1 genes shared syntenic relationships with PHT1 members in Arabidopsis thaliana, B. rapa, and B. oleracea, and that whole-genome duplication (polyploidy) played a major driving force for BnaPHT1 evolution in addition to segmental duplication. Transcript abundance analysis showed that a broad range of expression patterns of individual BnaPHT1 genes occurred in response to phosphorus (P) deficiency. In addition, the expression levels of BnaPHT1 genes can be regulated by different nutrient stresses, including nitrogen (N), potassium (K), sulfur (S) and iron (Fe) stresses. Moveover, salt and drought stresses can regulate the transcript abundances of BnaPHT1s, as well as phytohormones including auxin and cytokinin. Gene coexpression analysis based on the RNA-seq data implied that BnaPHT1s might cooperate with each other as well as with other genes to regulate nutrient homeostasis in B. napus. Further analysis of the promoters revealed that GT-1, DRE and P1BS elements are widely distributed within the promoter regions of BnaPHT1 genes. Our results indicate that BnaPHT1s might be involved in cross-talk for sensing the external status of P, N, K, S and Fe, as well as salt and drought stresses. Moreover, these processes might be mediated by phytohormones. Our findings provide the first step in the complex genetic dissection of the Pi transport system in plants and implicate multiple transcriptional regulation, which probably refers to new roles of PHT1 genes in B. napus.

Integrative Analysis of the Wheat PHT1 Gene Family Reveals A Novel Member Involved in Arbuscular Mycorrhizal Phosphate Transport and Immunity

Phosphorus (P) deficiency is one of the main growth-limiting factors for plants. However, arbuscular mycorrhizal (AM) symbiosis can significantly promote P uptake. Generally, PHT1 transporters play key roles in plants' P uptake, and thus, PHT1 genes have been investigated in some plants, but the regulation and functions of these genes in wheat (TaPHT1) during AM symbiosis have not been studied in depth. Therefore, a comprehensive analysis of TaPHT1 genes was performed, including sequence, phylogeny, cis-elements, expression, subcellular localization and functions, to elucidate their roles in AM-associated phosphate transport and immunity. In total, 35 TaPHT1s were identified in the latest high-quality bread wheat genome, 34 of which were unevenly distributed on 13 chromosomes, and divided into five groups. Sequence analysis indicated that there are 11 types of motif architectures and five types of exon-intron structures in the TaPHT1 family. Duplication mode analysis indicated that the TaPHT1 family has expanded mainly through segmental and tandem duplication events, and that all duplicated gene pairs have been under purifying selection. Transcription analysis of the 35 TaPHT1s revealed that not only known the mycorrhizal-specific genes TaPht-myc, TaPT15-4B (TaPT11) and TaPT19-4D (TaPT10), but also four novel mycorrhizal-specific/inducible genes (TaPT3-2D, TaPT11-4A, TaPT29-6A, and TaPT31-7A) are highly up-regulated in AM wheat roots. Furthermore, the mycorrhizal-specific/inducible genes are significantly induced in wheat roots at different stages of infection by colonizing fungi. Transient Agrobacterium tumefaciens-mediated transformation expression in onion epidermal cells showed that TaPT29-6A is a membrane-localized protein. In contrast to other AM-specific/inducible PHT1 genes, TaPT29-6A is apparently required for the symbiotic and direct Pi pathway. TaPT29-6A-silenced lines exhibited reduced levels of AM fungal colonization and arbuscules, but increased susceptibility to biotrophic, hemi-biotrophic and necrotrophic pathogens. In conclusion, TaPT29-6A was not only essential for the AM symbiosis, but also played vital roles in immunity.