Repression of Mitochondrial Citrate Synthase Genes by Aluminum Stress in Roots of Secale cereale and Brachypodium distachyon.

Aluminum (Al) toxicity in acid soils influences plant development and yield. Almost 50% of arable land is acidic. Plants have evolved a variety of tolerance mechanisms for Al. In response to the presence of Al, various species exudate citrate from their roots. Rye (Secale cereale L.) secretes both citrate and malate, making it one of the most Al-tolerant cereal crops. However, no research has been done on the role of the mitochondrial citrate synthase (mCS) gene in Al-induced stress in the rye. We have isolated an mCS gene, encoding a mitochondrial CS isozyme, in two S. cereale cultivars (Al-tolerant cv. Ailés and Al-sensitive inbred rye line Riodeva; ScCS4 gene) and in two Brachypodium distachyon lines (Al-tolerant ABR8 line and Al-sensitive ABR1 line; BdCS4 gene). Both mCS4 genes have 19 exons and 18 introns. The ScCS4 gene was located on the 6RL rye chromosome arm. Phylogenetic studies using cDNA and protein sequences have shown that the ScCS4 gene and their ScCS protein are orthologous to mCS genes and CS proteins of different Poaceae plants. Expression studies of the ScCS4 and BdSC4 genes show that the amount of their corresponding mRNAs in the roots is higher than that in the leaves and that the amounts of mRNAs in plants treated and not treated with Al were higher in the Al-tolerant lines than that in the Al-sensitive lines of both species. In addition, the levels of ScCS4 and BdCS4 mRNAs were reduced in response to Al (repressive behavior) in the roots of the tolerant and sensitive lines of S. cereale and B. distachyon.

Neutral molecular markers support common origin of aluminium tolerance in three congeneric grass species growing in acidic soils.

Aluminium (Al) toxicity is the main abiotic stress limiting plant productivity in acidic soils that are widely distributed among arable lands. Plant species differ in the level of Al resistance showing intraspecific and interspecific variation in many crop species. However, the origin of Al-tolerance is not well known. Three annual species, difficult to distinguish phenotypically and that were until recently misinterpreted as a single complex species under Brachypodium distachyon, have been recently separated into three distinct species: the diploids B. distachyon (2n = 10) and B. stacei (2n = 20), and B. hybridum (2n = 30), the allotetraploid derived from the two diploid species. The aims of this work were to know the origin of Al-tolerance in acidic soil conditions within these three Brachypodium species and to develop new DNA markers for species discrimination. Two multiplex SSR-PCRs allowed to genotype a group of 94 accessions for 17 pentanucleotide microsatellite (SSRs) loci. The variability for 139 inter-microsatellite (ISSRs) markers was also examined. The genetic relationships obtained using those neutral molecular markers (SSRs and ISSRs) support that all Al-tolerant allotetraploid accessions of B. hybridum have a common origin that is related with both geographic location and acidic soils. The possibility that the adaptation to acidic soils caused the isolation of the tolerant B. hybridum populations from the others is discussed. We finally describe a new, easy, DNA barcoding method based in the upstream-intron 1 region of the ALMT1 gene, a tool that is 100 % effective to distinguish among these three Brachypodium species.

Brachypodium distachyon: a model species for aluminium tolerance in Poaceae.

Aluminium (Al) toxicity is the main abiotic stress limiting plant productivity in acidic soils. Studies on Al tolerance have been conducted in Poaceae but their genomes are very complex. Fifty-nine diploid lines (2n=10) of Brachypodium distachyon (L.) P. Beauv. and 37 allotetraploid samples (2n=30) of Brachypodium hybridum Catalán, Joch. Müll., Hasterok & Jenkins sp. nov. were used to evaluate their tolerance to different Al concentrations. B. distachyon is Al-sensitive compared with oat, rice and rye. The diploid lines (except ABR8) were sensitive like barley and Arabidopsis; however, 10 allotetraploid samples were Al-tolerant. Four different root-staining methods were used to detect Al accumulation, cell death, lipid peroxidation and H2O2 production in diploid and allotetraploid plants. The roots treated with Al showed more intense staining in sensitive than tolerant lines. Also, without any staining, the Al treated roots of sensitive plants appear darker than roots from tolerant ones. The study concerning to the organic acids exudation shows that the exudation of citrate and malate was induced only in the roots from tolerant diploid line (ABR8) and tolerant allotetraploid samples. In contrast, the mRNA expression changes of several candidate genes for Al-activated transporters belonging to the ALMT and MATE families were analysed by quantitative PCR (qRT-PCR). The data obtained indicate that the transcripts from BdALMT1, BdMATE1 and BdMATE2 were present mainly in roots and, moreover, that the BdALMT1 transcript is present in higher amounts in the tolerant ABR8 than in the sensitive ABR1 plants indicating that this gene may be involved in Al tolerance. Finally, an insertion was detected in the promoter region of the BdALMT1 of tolerant diploid and allotetraploid plants.

Allelic frequencies of the 15 STR loci included in the AmpFlSTR Identifiler PCR Amplification Kit in an autochthonous sample from Spain.

The aim of this study was to estimate the allelic frequencies of the 15 STR loci included in the AmpFlSTR Identifiler PCR Amplification Kit in a sample of 342 unrelated Caucasian individuals autochthonous from Spain to be used for forensic purposes and population studies. The combined power of discrimination and the combined power of exclusion for all of the 15 loci were 5.68x10(-18) and 0.9999964, respectively. According to the obtained data, the D18S51 locus may be considered the most informative among the tested loci.

Genic heterozygosity, chromosomal interchanges and fitness in rye: any relationship?

Relationship between heterozygosity at allozyme loci, chromosomal interchanges and fitness was analyzed in a rye cultivar showing a polymorphism for such rearrangements. Nine allozyme systems (ACO, ACPH, GOT, GPI, LAP, MDH, PER, PGD and PGM) and five components of fitness (number of fertile tillers, total offspring, egg cell fertility, flowers/ear and seeds/ear) were studied. The estimated selection coefficients against interchange heterozygotes ranged from s = 0.12 to s = 0.34. A significant effect of the genic heterozygosity on some fitness components was observed in interchange heterozygotes (tillering and total offspring), in their standard homozygous sibs (flowers/ear and seeds/ear) and in the descendants of the crosses between standard karyotypes (flowers/ear, seeds/ear and egg cell fertility). However, the main effect was linked to genetic background associated to different crosses. Significant differences for Acph-1, Gpi-1, Lap-1, Mdh-1, Mdh-4, Pgd-2 and Pgm-1 loci were also found in some of these crosses although these differences were inconsistent. This suggests that probably the allozyme loci analyzed were not directly contributing to the fitness and that they are linked, in some cases, to different deleterious alleles depending on both cross and locus. This fact could support the local effect hypothesis as explanation although we do not discard the existence of some inbreeding level (general effect hypothesis) since all crosses and loci studied show a overall consistent trend of increased fitness with increased heterozygosity.