Overexpression of the CBF2 transcriptional activator in Arabidopsis delays leaf senescence and extends plant longevity

Leaf senescence is a programmed developmental process governed by various endogenous and exogenous factors, such as the plant developmental stage, leaf age, phytohormone levels, darkness, and exposure to stresses. It was found that, in addition to its well-documented role in the enhancement of plant frost tolerance, overexpression of the C-repeat/dehydration responsive element binding factor 2 (CBF2) gene in Arabidopsis delayed the onset of leaf senescence and extended the life span of the plants by approximately 2 weeks. This phenomenon was exhibited both during developmental leaf senescence and during senescence of detached leaves artificially induced by either darkness or phytohormones. Transcriptome analysis using the Affymetrix ATH1 genome array revealed that overexpression of CBF2 significantly influenced the expression of 286 genes in mature leaf tissue. In addition to 30 stress-related genes, overexpression of CBF2 also affected the expression of 24 transcription factor (TF) genes, and 20 genes involved in protein metabolism, degradation, and post-translational modification. These results indicate that overexpression of CBF2 not only increases frost tolerance, but also affects other developmental processes, most likely through interactions with additional TFs and protein modification genes. The present findings shed new light on the crucial relationship between plant stress tolerance and longevity, as reported for other eukaryotic organisms

Single-Nucleotide Polymorphism Markers from De-Novo Assembly of the Pomegranate Transcriptome Reveal Germplasm Genetic Diversity

<div><p>Pomegranate is a valuable crop that is grown commercially in many parts of the world. Wild species have been reported from India, Turkmenistan and Socotra. Pomegranate fruit has a variety of health-beneficial qualities. However, despite this crop's importance, only moderate effort has been invested in studying its biochemical or physiological properties or in establishing genomic and genetic infrastructures. In this study, we reconstructed a transcriptome from two phenotypically different accessions using 454-GS-FLX Titanium technology. These data were used to explore the functional annotation of 45,187 fully annotated contigs. We further compiled a genetic-variation resource of 7,155 simple-sequence repeats (SSRs) and 6,500 single-nucleotide polymorphisms (SNPs). A subset of 480 SNPs was sampled to investigate the genetic structure of the broad pomegranate germplasm collection at the Agricultural Research Organization (ARO), which includes accessions from different geographical areas worldwide. This subset of SNPs was found to be polymorphic, with 10.7% loci with minor allele frequencies of (MAF<0.05). These SNPs were successfully used to classify the ARO pomegranate collection into two major groups of accessions: one from India, China and Iran, composed of mainly unknown country origin and which was more of an admixture than the other major group, composed of accessions mainly from the Mediterranean basin, Central Asia and California. This study establishes a high-throughput transcriptome and genetic-marker infrastructure. Moreover, it sheds new light on the genetic interrelations between pomegranate species worldwide and more accurately defines their genetic nature.</p></div

Worldwide distribution of the pomegranate genetic groups.

<p>The genetic groups as clustered together by the genetic dendrogram were located on a world map by geographical regions. Genetic groups and subgroups are colored as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088998#pone-0088998-g006" target="_blank">Figure 6</a>.</p

Distribution of top homologs according to their taxonomy.

<p>The assembled contigs were submitted to sequence-similarity search (blastx) against the nonredundant protein (nr) GenBank database. The frequency of best-hit species was counted and is illustrated in a bar plot. Only species with more than 100 hits are presented.</p

Assembly parameters for ‘Nana’ and ‘Black’ accession reads.

<p>Assembly parameters for ‘Nana’ and ‘Black’ accession reads.</p

Pomegranate gene ontology categories.

<p>Contigs were annotated by blast hits against the nr database and mapped to GO categories by Blast2GO. The distribution of contigs into the GO categories biological processes, molecular functions, and cellular components is plotted for a pool of tissues (root, leaf, flower and fruit developmental stage 3; red bars) and from peel (turquoise bars).</p