A long and stressful day: Photoperiod shapes aluminium tolerance in plants.

Aluminium (Al), a limiting factor for crop productivity in acidic soils (pH ≤ 5.5), imposes drastic constraints for food safety in developing countries. The major mechanisms that allow plants to cope with Al involve manipulations of organic acids metabolism and DNA-checkpoints. When assumed individually both approaches have been insufficient to overcome Al toxicity. On analysing the centre of origin of most cultivated plants, we hypothesised that day-length seems to be a pivotal agent modulating Al tolerance across distinct plant species. We observed that with increasing distance from the Equator, Al tolerance decreases, suggesting a relationship with the photoperiod. We verified that long-day (LD) species are generally more Al-sensitive than short-day (SD) species, whereas genetic conversion of tomato for SD growth habit boosts Al tolerance. Reduced Al tolerance correlates with DNA-checkpoint activation under LD. Furthermore, DNA-checkpoint-related genes are under positive selection in Arabidopsis accessions from regions with shorter days, suggesting that photoperiod act as a selective barrier for Al tolerance. A diel regulation and genetic diversity affect Al tolerance, suggesting that day-length orchestrates Al tolerance. Altogether, photoperiodic control of Al tolerance might contribute to solving the historical obstacle that imposes barriers for developing countries to reach a sustainable agriculture.

Searching an auxinic herbicide to use as positive control in toxicity assays.

Due to rising concerns for environmental and human health, many toxic compounds, such as auxin-based herbicides, have been tested in relation their toxicity effect. Especially cyto- and phytotoxic assays have been performed on a number monocot and eudicot plant species. In these approaches the toxicity level of the auxin is compared to a positive control - usually a commercial compound with known effects and chemical similarity to the target compound. However, many target compounds still lack an indication of an adequate positive control. Here, we evaluate the phytotoxic and cytotoxic effect of the auxins 2,4-dichlorophenoxyacetic acid, dicamba, and picloram in order test their potential use as positive controls. All tested auxinic herbicides showed clastogenic and aneugenic effect mechanisms. The results indicate 2,4-dichlorophenoxyacetic acid as the most phyto- and cytotoxic in the discontinuous method in Lactuca sativa L. and Allium cepa L., and also in the continuous method in A. cepa. Thus, we suggest 2,4-dichlorophenoxyacetic acid as a positive control for future mutagenesis studies involving new auxins. For studies with L. sativa in continuous method, we recommend the auxin picloram as positive control as this one was the only one which allowed the development of roots.

New Insights Into the Evolution of C4 Photosynthesis Offered by the Tarenaya Cluster of Cleomaceae.

Cleomaceae is closely related to Brassicaceae and includes C3, C3-C4, and C4 species. Thus, this family represents an interesting system for studying the evolution of the carbon concentrating mechanism. However, inadequate genetic information on Cleomaceae limits their research applications. Here, we characterized 22 Cleomaceae accessions [3 genera (Cleoserrata, Gynandropsis, and Tarenaya) and 11 species] in terms of genome size; molecular phylogeny; as well as anatomical, biochemical, and photosynthetic traits. We clustered the species into seven groups based on genome size. Interestingly, despite clear differences in genome size (2C, ranging from 0.55 to 1.3 pg) in Tarenaya spp., this variation was not consistent with phylogenetic grouping based on the internal transcribed spacer (ITS) marker, suggesting the occurrence of multiple polyploidy events within this genus. Moreover, only G. gynandra, which possesses a large nuclear genome, exhibited the C4 metabolism. Among the C3-like species, we observed intra- and interspecific variation in nuclear genome size as well as in biochemical, physiological, and anatomical traits. Furthermore, the C3-like species had increased venation density and bundle sheath cell size, compared to C4 species, which likely predisposed the former lineages to C4 photosynthesis. Accordingly, our findings demonstrate the potential of Cleomaceae, mainly members of Tarenaya, in offering novel insights into the evolution of C4 photosynthesis.

Karyotype characterization and nuclear DNA content measurement in Bromeliaceae: state of the art and future perspectives.

In Bromeliaceae, cytogenetic and flow cytometry analyses have been performed to clarify systematic and evolutionary aspects. Karyotyping approaches have shown the relatively high chromosome number, similar morphology and small size of the chromosomes. These facts have prevented a correct chromosome counting and characterization. Authors have established a basic chromosome number of x = 25 for Bromeliaceae. Recently, one karyomorphological analysis revealed that x = 25 is no longer the basic chromosome number, whose genome may have a polyploid origin. Besides cytogenetic characterization, the 2C DNA content of bromeliads has been measured. Nuclear DNA content has varied from 2C = 0.60 to 2C = 3.34 picograms. Thus, in relation to most angiosperms, the 2C DNA content of Bromeliaceae species as well as their chromosome size can be considered relatively small. In spite of some advances, cytogenetic and flow cytometry data are extremely scarce in this group. In this context, this review reports the state of the art in karyotype characterization and nuclear DNA content measurement in Bromeliaceae, emphasizing the main problems and suggesting prospective solutions and ideas for future research.

The soybean sucrose binding protein gene family: genomic organization, gene copy number and tissue-specific expression of the SBP2 promoter.

The sucrose binding protein (SBP) from soybean has been implicated as an important component of the sucrose uptake system. Two SBP genomic clones, gsS641.1 and gsS641.2, which correspond to allelic forms of the GmSBP2/S64 gene, have been isolated and characterized. As a member of the seed storage protein superfamily, it has been shown that the SBP gene structure is similar to vicilin genes with intron/exon boundaries at conserved positions. Fluores cence in situ hybridization (FISH) suggested that the soybean SBP gene family is represented by at least two non-allelic genes corresponding to the previously isolated GmSBP1 and GmSBP2/S64 cDNAs. These two cDNAs share extensive sequence similarity but are located at different loci in the soybean genome. To investigate transcriptional activation of the GmSBP2 gene, 2 kb 5'-flanking sequences of gsS641.1 and gsS641.2 were fused to the beta-glucuronidase (GUS) reporter gene and to the green fluorescent protein (GFP) reporter gene and inde pendently introduced into Nicotiana tabacum by Agrobacterium tumefaciens-mediated transformation. The SBP2 promoter directed expression of both GUS and GFP reporter genes with high specificity to the phloem of leaves, stems and roots. Thus, the overall pattern of SBP-GUS or SBP-GFP expression is consistent with the involvement of SBP in sucrose translocation-dependent physiological processes.