Phytoremediation of chromium using Salix species: cloning ESTs and candidate genes involved in the Cr response.

In this research a differential display based on the detection of cDNA-AFLP markers was used to identify candidate genes potentially involved in the regulation of the response to chromium in four different willow species (Salix alba, Salix eleagnos, Salix fragilis and Salix matsudana) chosen on the basis of their suitability in phytoremediation techniques. Our approach enabled the assay of a large set of mRNA-related fragments and increased the reliability of amplification-based transcriptome analysis. The vast majority of transcript-derived fragments were shared among samples within species and thus attributable to constitutively expressed genes. However, a number of differentially expressed mRNAs were scored in each species and a total of 68 transcripts displaying an altered expression in response to Cr were isolated and sequenced. Public database querying revealed that 44.1% and 4.4% of the cloned ESTs score significant similarity with genes encoding proteins having known or putative function, or with genes coding for unknown proteins, respectively, whereas the remaining 51.5% did not retrieve any homology. Semi-quantitative RT-PCR analysis of seven candidate genes fully confirmed the expression patterns obtained by cDNA-AFLP. Our results indicate the existence of common mechanisms of gene regulation in response to Cr, pathogen attack and senescence-mediated programmed cell death, and suggest a role for the genes isolated in the cross-talk of the signaling pathways governing the adaptation to biotic and abiotic stresses.

Alfalfa Mob 1-like genes are expressed in reproductive organs during meiosis and gametogenesis.

Mps-one-binder (Mob) proteins play an important role in chromosome separation and cell plate formation in yeast. We cloned two Mob 1-like genes from alfalfa (Medicago sativa L.) and show that one gene is constitutively expressed while the other is expressed only in flower buds during sporogenesis and gametogenesis. For the analysis of gene expression during reproduction in alfalfa wild-types and apomeiotic mutants, a specific antisense riboprobe was designed for MsMob 1 transcripts and a polyclonal antibody was raised against MsMob 1 proteins. In situ mRNA localization as well as protein immunolocalization proved that MsMob1-like genes are specifically expressed in degenerating megaspores of normal ovules and in enlarged megaspore mother cells and embryo sacs of apomeiotic ovules. Gene products were also found in microspore tetrads at the beginning of pollen development as well as in tapetum cells of anthers undergoing programmed cell death to allow pollen dispersal at maturity. Overall results suggest that MsMob 1-like genes can play a key role during the reproductive pathway in plants.