Local and systemic responses conferring acclimation of Brassica napus roots to low phosphorus conditions

The Discovery of Highly Efficient and Promising ABA Receptor Antagonists for Agricultural Applications Based on APAn Modification

Abscisic acid (ABA) is one of the many naturally occurring phytohormones widely found in plants. This study focused on refining APAn, a series of previously developed agonism/antagonism switching probes. Twelve novel APAn analogues were synthesized by introducing varied branched or oxygen-containing chains at the C-6' position, and these were screened. Through germination assays conducted on A. thaliana, colza, and rice seeds, as well as investigations into stomatal movement, several highly active ABA receptor antagonists were identified. Microscale thermophoresis (MST) assays, molecular docking, and molecular dynamics simulation showed that they had stronger receptor affinity than ABA, while PP2C phosphatase assays indicated that the C-6'-tail chain extending from the 3' channel effectively prevented the ligand-receptor binary complex from binding to PP2C phosphatase, demonstrating strong antagonistic activity. These antagonists showed effective potential in promoting seed germination and stomatal opening of plants exposed to abiotic stress, particularly cold and salt stress, offering advantages for cultivating crops under adverse conditions. Moreover, their combined application with fluridone and gibberellic acid could provide more practical agricultural solutions, presenting new insights and tools for overcoming agricultural challenges.

Trade-offs between root-secreted acid phosphatase and root morphology traits, and their contribution to phosphorus acquisition in Brassica napus

Oilseed rape (Brassica napus) is one of the most important oil crops in the world and shows sensitivity to low phosphorus (P) availability. In many soils, organic P (Po) is the main component of the soil P pool. Po must be mineralised to Pi through phosphatases, and then taken up by plants. However, the relationship between root-secreted acid phosphatases (APase) and root morphology traits, two important P-acquisition strategies in response to P deficiency, is unclear among B. napus genotypes. This study aimed to understand their relationship and how they affect P acquisition, which is crucial for the sustainable utilisation of agricultural P resources. This study showed significant genotypic variations in root-secreted APase activity per unit root fresh weight (SAP) and total root-secreted APase activity per plant (total SAP) among 350 B. napus genotypes. Seed yield was positively correlated with total SAP but not significantly correlated with SAP. Six root traits of 18 B. napus genotypes with contrasting root biomass were compared under normal Pi, low Pi and Po. Genotypes with longer total root length (TRL) reduced SAP, but those with shorter TRL increased SAP under P deficiency. Additionally, TRL was important in P-acquisition under three P treatments, and total SAP was also important in P-acquisition under Po treatment. In conclusion, trade-offs existed between the two P-acquisition strategies among B. napus genotypes under P-deficient conditions. Total SAP was an important root trait under Po conditions. These results might help to breed B. napus with greater P-acquisition ability under low P availability conditions.

PHR1 involved in the regulation of low phosphate-induced leaf senescence by modulating phosphorus homeostasis in Arabidopsis

Phosphorus (P) is a crucial macronutrient for plant growth, development, and reproduction. The effects of low P (LP) stress on leaf senescence and the role of PHR1 in LP-induced leaf senescence are still unknown. Here, we report that PHR1 plays a crucial role in LP-induced leaf senescence, showing delayed leaf senescence in phr1 mutant and accelerated leaf senescence in 35S:PHR1 transgenic Arabidopsis under LP stress. The transcriptional profiles indicate that 763 differentially expressed SAGs (DE-SAGs) were upregulated and 134 DE-SAGs were downregulated by LP stress. Of the 405 DE-SAGs regulated by PHR1, 27 DE-SAGs were involved in P metabolism and transport. PHR1 could bind to the promoters of six DE-SAGs (RNS1, PAP17, SAG113, NPC5, PLDζ2, and Pht1;5), and modulate them in LP-induced senescing leaves. The analysis of RNA content, phospholipase activity, acid phosphatase activity, total P and phosphate content also revealed that PHR1 promotes P liberation from senescing leaves and transport to young tissues under LP stress. Our results indicated that PHR1 is one of the crucial modulators for P recycling and redistribution under LP stress, and the drastic decline of P level is at least one of the causes of early senescence in P-deficient leaves.

Brassinosteroid signaling regulates phosphate starvation-induced malate secretion in plants

Inorganic phosphate (Pi) is often limited in soils due to precipitation with iron (Fe) and aluminum (Al). To scavenge heterogeneously distributed phosphorus (P) resources, plants have evolved a local Pi signaling pathway that induces malate secretion to solubilize the occluded Fe-P or Al-P oxides. In this study, we show that Pi limitation impaired brassinosteroid signaling and downregulated BRASSINAZOLE-RESISTANT 1 (BZR1) expression in Arabidopsis thaliana. Exogenous 2,4-epibrassinolide treatment or constitutive activation of BZR1 (in the bzr1-D mutant) significantly reduced primary root growth inhibition under Pi-starvation conditions by downregulating ALUMINUM-ACTIVATED MALATE TRANSPORTER 1 (ALMT1) expression and malate secretion. Furthermore, AtBZR1 competitively suppressed the activator effect of SENSITIVITY TO PROTON RHIZOTOXICITY 1 (STOP1) on ALMT1 expression and malate secretion in Nicotiana benthamiana leaves and Arabidopsis. The ratio of nuclear-localized STOP1 and BZR1 determined ALMT1 expression and malate secretion in Arabidopsis. In addition, BZR1-inhibited malate secretion is conserved in rice (Oryza sativa). Our findings provide insight into plant mechanisms for optimizing the secretion of malate, an important carbon resource, to adapt to Pi-deficiency stress.

Rapid identification of a major locus qPRL-C06 affecting primary root length in Brassica napus by QTL-seq

BACKGROUND AND AIMS

Brassica napus is one of the most important oilseed crops worldwide. Seed yield of B. napus significantly correlates with the primary root length (PRL). The aims of this study were to identify quantitative trait loci (QTLs) for PRL in B. napus.

METHODS

QTL-seq and conventional QTL mapping were jointly used to detect QTLs associated with PRL in a B. napus double haploid (DH) population derived from a cross between 'Tapidor' and 'Ningyou 7'. The identified major locus was confirmed and resolved by an association panel of B. napus and an advanced backcross population. RNA-seq analysis of two long-PRL lines (Tapidor and TN20) and two short-PRL lines (Ningyou 7 and TN77) was performed to identify differentially expressed genes in the primary root underlying the target QTLs.

KEY RESULTS

A total of 20 QTLs impacting PRL in B. napus grown at a low phosphorus (P) supply were found by QTL-seq. Eight out of ten QTLs affecting PRL at a low P supply discovered by conventional QTL mapping could be detected by QTL-seq. The locus qPRL-C06 identified by QTL-seq was repeatedly detected at both an optimal P supply and a low P supply by conventional QTL mapping. This major constitutive QTL was further confirmed by regional association mapping. qPRL-C06 was delimited to a 0.77 Mb genomic region on chromosome C06 using an advanced backcross population. A total of 36 candidate genes within qPRL-C06 were identified that showed variations in coding sequences and/or exhibited significant differences in mRNA abundances in primary root between the long-PRL and short-PRL lines, including five genes involved in phytohormone biosynthesis and signaling.

CONCLUSIONS

These results both demonstrate the power of the QTL-seq in rapid QTL detection for root traits and will contribute to marker-assisted selective breeding of B. napus cultivars with increased PRL.

Genome-Scale Investigation of GARP Family Genes Reveals Their Pivotal Roles in Nutrient Stress Resistance in Allotetraploid Rapeseed

The GARP genes are plant-specific transcription factors (TFs) and play key roles in regulating plant development and abiotic stress resistance. However, few systematic analyses of GARPs have been reported in allotetraploid rapeseed (Brassica napus L.) yet. In the present study, a total of 146 BnaGARP members were identified from the rapeseed genome based on the sequence signature. The BnaGARP TFs were divided into five subfamilies: ARR, GLK, NIGT1/HRS1/HHO, KAN, and PHL subfamilies, and the members within the same subfamilies shared similar exon-intron structures and conserved motif configuration. Analyses of the Ka/Ks ratios indicated that the GARP family principally underwent purifying selection. Several cis-acting regulatory elements, essential for plant growth and diverse biotic and abiotic stresses, were identified in the promoter regions of BnaGARPs. Further, 29 putative miRNAs were identified to be targeting BnaGARPs. Differential expression of BnaGARPs under low nitrate, ammonium toxicity, limited phosphate, deficient boron, salt stress, and cadmium toxicity conditions indicated their potential involvement in diverse nutrient stress responses. Notably, BnaA9.HHO1 and BnaA1.HHO5 were simultaneously transcriptionally responsive to these nutrient stresses in both hoots and roots, which indicated that BnaA9.HHO1 and BnaA1.HHO5 might play a core role in regulating rapeseed resistance to nutrient stresses. Therefore, this study would enrich our understanding of molecular characteristics of the rapeseed GARPs and will provide valuable candidate genes for further in-depth study of the GARP-mediated nutrient stress resistance in rapeseed.