Whilst constitutive overexpression of particular acid phosphatases (APases) can increase utilization of extracellular organic phosphate, negative effects are frequently observed in these transgenic plants under conditions of inorganic phosphate (Pi) sufficiency. In this study, we identified rice purple acid phosphatase 10c (OsPAP10c) as being a novel and major APase that exhibits activities associated both with the root surface and with secretion. Two constructs were used to generate the OsPAP10c-overexpression plants by driving its coding sequence with either a ubiquitin promoter (UP) or the OsPAP10c-native promoter (NP). Compared with the UP transgenic plants, lower expression levels and APase activities were observed in the NP plants. However, the UP and NP plants both showed a similar ability to degrade extracellular ATP and both promoted root growth. The growth performance and yield of the NP transgenic plants were better than the wild-type and UP plants in both hydroponic and field experiments irrespective of the level of Pi supply. Overexpression of APase by its native promoter therefore provides a potential way to improve crop production that might avoid increased APase activity in untargeted tissues and its inhibition of the growth of transgenic plants.

Background: The gene FLOWERING LOCUS T (FT) and its orthologues play a central role in the integration of flowering signals within Arabidopsis and other diverse species. Multiple copies of FT, with different cis-intronic sequence, exist and appear to operate harmoniously within polyploid crop species such as Brassica napus (AACC), a member of the same plant family as Arabidopsis. Results: We have identified six BnFT paralogues from the genome of B. napus and mapped them to six distinct regions, each of which is homologous to a common ancestral block (E) of Arabidopsis chromosome 1. Four of the six regions were present within inverted duplicated regions of chromosomes A7 and C6. The coding sequences of BnFT paralogues showed 92-99% identities to each other and 85-87% identity with that of Arabidopsis. However, two of the paralogues on chromosomes A2 and C2, BnA2.FT and BnC2.FT, were found to lack the distinctive CArG box that is located within intron 1 that has been shown in Arabidopsis to be the binding site for theFLC protein. Three BnFT paralogues (BnA2.FT, BnC6.FT.a and BnC6.FT.b) were associated with two major QTL clusters for flowering time. One of the QTLs encompassing two BnFT paralogues (BnC6.FT.a and BnC6.FT.b) on chromosome C6 was resolved further using near isogenic lines, specific alleles of which were both shown to promote flowering. Association analysis of the three BnFT paralogues across 55 cultivars of B. napus showed that the alleles detected in the original parents of the mapping population used to detect QTL (NY7 and Tapidor) were ubiquitous amongst spring and winter type cultivars of rapeseed. It was inferred that the ancestral FT homologues in Brassica evolved from two distinct copies, one of which was duplicated along with inversion of the associated chromosomal segment prior to the divergence of B. rapa (AA) and B. oleracea (CC). At least ten such inverted duplicated blocks (IDBs) were identified covering a quarter of the whole B. napus genome. Conclusion: Six orthologues of Arabidopsis FT were identified and mapped in the genome of B. napus which sheds new light on the evolution of paralogues in polyploidy species. The allelic variation of BnFT paralogues results in functional differences affecting flowering time between winter and spring type cultivars of oilseed Brassica. The prevalent inverted duplicated blocks, two of which were located by four of the six BnFT paralogues, contributed to gene duplications and might represent predominant pathway of evolution in Brassica.

Background: FAE1 (fatty acid elongase1) is the key gene in the control of erucic acid synthesis in seeds of Brassica species. Due to oil with low erucic acid (LEA) content is essential for human health and not enough LEA resource could be available, thus new LEA genetic resources are being sought for Brassica breeding. EcoTILLING, a powerful genotyping method, can readily be used to identify polymorphisms in Brassica. Results: Seven B. rapa, nine B. oleracea and 101 B. napus accessions were collected for identification of FAE1 polymorphisms. Three polymorphisms were detected in the two FAE1 paralogues of B. napus using EcoTILLING and were found to be strongly associated with differences in the erucic acid contents of seeds. In genomic FAE1 sequences obtained from seven B. rapa accessions, one SNP in the coding region was deduced to cause loss of gene function. Molecular evolution analysis of FAE1 homologues showed that the relationship between the Brassica A and C genomes is closer than that between the A/C genomes and Arabidopsis genome. Alignment of the coding sequences of these FAE1 homologues indicated that 18 SNPs differed between the A and C genomes and could be used as genome-specific markers in Brassica. Conclusion: This study showed the applicability of EcoTILLING for detecting gene polymorphisms in Brassica. The association between B. napus FAE1 polymorphisms and the erucic acid contents of seeds may provide useful guidance for LEA breeding. The discovery of the LEA resource in B. rapa can be exploited in Brasscia cultivation.

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.

Key message : A comprehensive linkage atlas for seed yield in rapeseed. Most agronomic traits of interest for crop improvement (including seed yield) are highly complex quantitative traits controlled by numerous genetic loci, which brings challenges for comprehensively capturing associated markers/genes. We propose that multiple trait interactions underlie complex traits such as seed yield, and that considering these component traits and their interactions can dissect individual quantitative trait loci (QTL) effects more effectively and improve yield predictions. Using a segregating rapeseed (Brassica napus) population, we analyzed a large set of trait data generated in 19 independent experiments to investigate correlations between seed yield and other complex traits, and further identified QTL in this population with a SNP-based genetic bin map. A total of 1904 consensus QTL accounting for 22 traits, including 80 QTL directly affecting seed yield, were anchored to the B. napus reference sequence. Through trait association analysis and QTL meta-analysis, we identified a total of 525 indivisible QTL that either directly or indirectly contributed to seed yield, of which 295 QTL were detected across multiple environments. A majority (81.5%) of the 525 QTL were pleiotropic. By considering associations between traits, we identified 25 yield-related QTL previously ignored due to contrasting genetic effects, as well as 31 QTL with minor complementary effects. Implementation of the 525 QTL in genomic prediction models improved seed yield prediction accuracy. Dissecting the genetic and phenotypic interrelationships underlying complex quantitative traits using this method will provide valuable insights for genomics-based crop improvement.