Semi-mangroves form a group of transitional species between glycophytes and halophytes, and hold unique potential for learning molecular mechanisms underlying plant salt tolerance. Millettia pinnata is a semi-mangrove plant that can survive a wide range of saline conditions in the absence of specialized morphological and physiological traits. By employing the Illumina sequencing platform, we generated ∼192 million short reads from four cDNA libraries of M. pinnata and processed them into 108 598 unisequences with a high depth of coverage. The mean length and total length of these unisequences were 606 bp and 65.8 Mb, respectively. A total of 54 596 (50.3%) unisequences were assigned Nr annotations. Functional classification revealed the involvement of unisequences in various biological processes related to metabolism and environmental adaptation. We identified 23 815 candidate salt-responsive genes with significantly differential expression under seawater and freshwater treatments. Based on the reverse transcription–polymerase chain reaction (RT–PCR) and real-time PCR analyses, we verified the changes in expression levels for a number of candidate genes. The functional enrichment analyses for the candidate genes showed tissue-specific patterns of transcriptome remodelling upon salt stress in the roots and the leaves. The transcriptome of M. pinnata will provide valuable gene resources for future application in crop improvement. In addition, this study sets a good example for large-scale identification of salt-responsive genes in non-model organisms using the sequencing-based approach.

Late embryogenesis abundant (LEA) group 4 (LEA4) proteins play an important role in the water stress tolerance of plants. Although they have been hypothesized to stabilize macromolecules in stressed cells, the protective functions and mechanisms of LEA4 proteins are still not clear. In this study, the metal binding properties of two related soybean LEA4 proteins, GmPM1 and GmPM9, were tested using immobilized metal ion affinity chromatography (IMAC). The metal ions Fe³⁺, Ni²⁺, Cu²⁺ and Zn²⁺ were observed to bind these two proteins, while Ca²⁺, Mg²⁺ or Mn²⁺ did not. Results from isothermal titration calorimetry (ITC) indicated that the binding affinity of GmPM1 for Fe³⁺ was stronger than that of GmPM9. Hydroxyl radicals generated by the Fe³⁺/H₂O₂ system were scavenged by both GmPM1 and GmPM9 in the absence or the presence of high ionic conditions (100 mM NaCl), although the scavenging activity of GmPM1 was significantly greater than that of GmPM9. These results suggest that GmPM1 and GmPM9 are metal-binding proteins which may function in reducing oxidative damage induced by abiotic stress in plants.

Avicennia marina is a widely distributed mangrove species that thrives in high-salinity habitats. It plays a significant role in supporting coastal ecosystem and holds unique potential for studying molecular mechanisms underlying ecological adaptation. Despite and sometimes because of its numerous merits, this species is facing increasing pressure of exploitation and deforestation. Both study on adaptation mechanisms and conservation efforts necessitate more genomic resources for A. marina. In this study, we used Illumina sequencing of an A. marina foliar cDNA library to generate a transcriptome dataset for gene and marker discovery. We obtained 40 million high-quality reads and assembled them into 91,125 unigenes with a mean length of 463 bp. These unigenes covered most of the publicly available A. marina Sanger ESTs and greatly extended the repertoire of transcripts for this species. A total of 54,497 and 32,637 unigenes were annotated based on homology to sequences in the NCBI non-redundant and the Swiss-prot protein databases, respectively. Both Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed some transcriptomic signatures of stress adaptation for this halophytic species. We also detected an extraordinary amount of transcripts derived from fungal endophytes and demonstrated the utility of transcriptome sequencing in surveying endophyte diversity without isolating them out of plant tissues. Additionally, we identified 3,423 candidate simple sequence repeats (SSRs) from 3,141 unigenes with a density of one SSR locus every 8.25 kb sequence. Our transcriptomic data will provide valuable resources for ecological, genetic and evolutionary studies in A. marina.

The plant-specific BURP family proteins play diverse roles in plant development and stress responses, but the function mechanism of these proteins is still poorly understood. Proteins in this family are characterized by a highly conserved BURP domain with four conserved Cys-His repeats and two other Cys, indicating that these proteins potentially interacts with metal ions. In this paper, an immobilized metal affinity chromatography (IMAC) assay showed that the soybean BURP protein SALI3-2 could bind soft transition metal ions (Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Cu²⁺) but not hard metal ions (Ca²⁺ and Mg²⁺) in vitro. A subcellular localization analysis by confocal laser scanning microscopy revealed that the SALI3-2-GFP fusion protein was localized to the vacuoles. Physiological indexes assay showed that Sali3-2-transgenic Arabidopsis thaliana seedlings were more tolerant to Cu²⁺ or Cd²⁺ stresses than the wild type. An inductively coupled plasma optical emission spectrometry (ICP-OES) analysis illustrated that, compared to the wild type seedlings the Sali3-2-transgenic seedlings accumulated more cadmium or copper in the roots but less in the upper ground tissues when the seedlings were exposed to excessive CuCl₂ or CdCl₂ stress. Therefore, our findings suggest that the SALI3-2 protein may confer cadmium (Cd²⁺) and copper (Cu²⁺) tolerance to plants by helping plants to sequester Cd²⁺ or Cu²⁺ in the root and reduce the amount of heavy metals transported to the shoots.