BackgroundSuperoxide dismutase (SOD) is an essential enzyme of the plant antioxidant system that responds to oxidative stresses caused by adverse conditions. Banana is an important staple and economic crop in tropical and subtropical regions. However, its growth and yield are constantly affected by various abiotic stresses. To analyze the roles of distinct SOD genes under various stresses, a detailed characterization and analysis of the SOD gene family in Cavendish banana is indispensable.MethodsThe presence and structure of the SOD family genes were experimentally verified using 5′/3′ RACE-PCR, reverse transcription PCR and PCR. Then, their syntenic relationships, conserved motifs and phylogenetic relationships were analyzed using software. Cis-elements present in the promoters were predicted via PlantCARE. And the expression levels under abiotic and hormonal stresses were determined using real-time quantitative polymerase chain reaction.ResultsIn total, 25 ‘Tianbaojiao’ SOD cDNAs (MaSODs), which encoded six Cu/ZnSODs, four MnSODs and two FeSODs, were cloned. The 12 MaSOD genes were divided into four groups based on their conserved motifs, which corroborated their classifications based on gene-structure patterns and subcellular localizations. Eleven MaSOD promoters were isolated and found to contain many cis-acting elements involved in stress responses. Gene expression analysis showed that 11 out of the 12 MaSODs were expressed in all tested tissues (leaf, pseudostem and root), whereas MaCSD2B was expressed only in leaves and roots. Specific MaSOD members exhibited different expression patterns under abiotic and hormonal treatments. Among the 12 MaSOD genes, MaCSD1D was the only one that responded to all eight treatments, suggesting that this gene plays a predominant role in reactive oxygen species scavenging caused by various stresses in banana.ConclusionsA genome-wide analysis showed that the ‘Tianbaojiao’ banana harbored an expanded SOD gene family. Whole genome duplication, segmental duplication and complex transcriptional regulation contributed to the gene expansion and mRNA diversity of the MaSODs. The expression patterns of distinct MaSOD genes showed that they are important responses to different abiotic and hormonal stresses in banana.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2046-7) contains supplementary material, which is available to authorized users.

The eukaryotic Ddi1 family is defined by a conserved retroviral aspartyl protease-like (RVP) domain found in association with a ubiquitin-like (UBL) domain. Ddi1 from Saccharomyces cerevisiae additionally contains a ubiquitin-associated (UBA) domain. The substrate specificity and role of the protease domain in the biological functions of the Ddi family remain unclear. Yeast Ddi1 has been implicated in the regulation of cell cycle progression, DNA-damage repair, and exocytosis. Here, we investigated the multi-domain structure of yeast Ddi1 using X-ray crystallography, nuclear magnetic resonance, and small-angle X-ray scattering. The crystal structure of the RVP domain sheds light on a putative substrate recognition site involving a conserved loop. Isothermal titration calorimetry confirms that both UBL and UBA domains bind ubiquitin, and that Ddi1 binds K48-linked diubiquitin with enhanced affinity. The solution NMR structure of a helical domain that precedes the protease displays tertiary structure similarity to DNA-binding domains from transcription regulators. Our structural studies suggest that the helical domain could serve as a landing platform for substrates in conjunction with attached ubiquitin chains binding to the UBL and UBA domains.

Differential concentrations of phytohormone trigger distinct outputs, which provides a mechanism for the plasticity of plant development and an adaptation strategy among plants to changing environments. However, the underlying mechanisms of the differential responses remain unclear. Here we report that a high concentration of auxin, distinct from the effect of low auxin concentration, enhances abscisic acid (ABA) responses in Arabidopsis thaliana, which partially relies on TRANS-MEMBERANE KINASE 1 (TMK1), a key regulator in auxin signaling. We show that high auxin and TMK1 play essential and positive roles in ABA signaling through regulating ABA INSENSITIVE 1 and 2 (ABI1/2), two negative regulators of the ABA pathway. TMK1 inhibits the phosphatase activity of ABI2 by direct phosphorylation of threonine 321 (T321), a conserved phosphorylation site in ABI2 proteins, whose phosphorylation status is important for both auxin and ABA responses. This TMK1-dependent auxin signaling in the regulation of ABA responses provides a possible mechanism underlying the high auxin responses in plants and an alternative mechanism involved in the coordination between auxin and ABA signaling.

Copper/zinc superoxide dismutases (Cu/ZnSODs) play important roles in improving banana resistance to adverse conditions, but their activities depend on the copper chaperone for superoxide dismutase (CCS) delivering copper to them. However, little is known about CCS in monocots and under stress conditions. Here, a novel CCS gene (MaCCS) was obtained from a banana using reverse transcription PCR and rapid-amplification of cDNA ends (RACE) PCR. Sequence analyses showed that MaCCS has typical CCS domains and a conserved gene structure like other plant CCSs. Alternative transcription start sites (ATSSs) and alternative polyadenylation contribute to the mRNA diversity of MaCCS. ATSSs in MaCCS resulted in one open reading frame containing two in-frame start codons to form two protein versions, which is supported by the MaCCS subcellular localization of in both cytosol and chloroplasts. Furthermore, MaCCS promoter was found to contain many cis-elements associated with abiotic and hormonal responses. Quantitative real-time PCR analysis showed that MaCCS was expressed in all tested tissues (leaves, pseudostems and roots). In addition, MaCCS expression was significantly induced by light, heat, drought, abscisic acid and indole-3-acetic acid, but inhibited by relatively high concentrations of CuSO4 and under cold treatment, which suggests that MaCCS is involved in abiotic and hormonal responses.

The in-vivo effect of vitamin K(2) on bone metabolism was investigated by histochemical and morphometric methods, using an animal model of osteoporosis. Eighteen female Wistar rats were divided into three groups. Rats in group A had sham ovariectomies, group B were ovariectomized, and group C were ovariectomized and received vitamin K(2), at 10 mg/kg per day, injected subcutaneously. The lumbar vertebral bones were evaluated 8 weeks after the operation by a modified tetrachrome method after decalcification. Mineralized bone areas, osteoid, and defectively mineralized bone areas in group B were markedly decreased compared with findings in group A, but these features in group C were not severely decreased. There was no significant difference in total bone areas and total bone volumes among the three groups. Accordingly, it appeared that vitamin K(2) had an effect in reducing mineralized bone loss after the ovariectomy. In conclusion, vitamin K(2) is thought to be beneficial for the properties of bone microarchitecture in the condition of osteoporosis.