Search

EaF82, a gene identified in previous studies of the variegated plant Epipremnum aureum, exhibited a unique expression pattern with greater transcript abundance in yellow sectors than green sectors of variegated leaves, but lower abundance in regenerated pale yellow plants than in green plants derived from leaf tissue culture. Studies of its full-length cDNA and promoter region revealed two members with only the EaF82a expressed. Immunoblotting confirmed that EaF82a encodes a 12 kDa protein and its accumulation consistent with its gene expression patterns in different color tissues. Transient expression of EaF82a-sGFP fusion proteins in protoplasts showed that EaF82a seems to be present in the cytosol as unidentified spots. Sequence motif search reveals a potential auxin responsive element in promoter region. Using transgenic Arabidopsis seedlings carrying EaF82a promoter driving the bacterial uidA (GUS) gene, an increased GUS activity was observed when IAA (indole-3-acetic acid) concentration was elevated. In E. aureum, EaF82a is more abundant at the site where axillary buds emerge and at the lower side of bending nodes where more IAA accumulates relative to the upper side. The measurement of endogenous IAA levels in different color tissues revealed the same pattern of IAA distribution as that of EaF82a expression, further supporting that EaF82a is an IAA responsive gene. EaF82a expression in etiolated transgenic Arabidopsis seedlings responded to IAA under the influence of light suggesting a microenvironment of uneven light condition affects the EaF82a transcript levels and protein accumulation in variegated leaves., (© 2014 Scandinavian Plant Physiology Society.)

The ubiquitin-proteasome pathway (UPP) coordinates a myriad of physiological processes in higher plants, including abiotic stress responses, but it is less well characterized in algal species. In this study, the green alga Chlamydomonas reinhardtii was used to gain insights into the role of the UPP during moderate and severe selenite stress at three different time points. The data indicate that activity of the UPP in response to selenium (Se) stress was both time and dose dependent. Moderate selenite stress increased proteasome activity, protein ubiquitination and the proteasomal removal of malformed selenoproteins. However, severe Se stress caused by prolonged selenite treatment or high selenite concentration decreased proteasome activity, inhibited protein ubiquitination and prevented the proteasomal removal of selenoproteins. The UPP impairment during severe Se stress was associated with the observed accumulation of reactive oxygen species (ROS), including mitochondrial superoxide. Additionally, proteasomal inhibition decreased the concentration of chlorophyll in cultures challenged with Se. Therefore, although the UPP protects Chlamydomonas against Se stress, severe oxidative stress induced by selenite toxicity likely hinders the UPP's capacity to mediate a stress response. The possibility that stress tolerance in plants is dependent upon optimal UPP activity and maintenance is discussed., (Published by Oxford University Press on behalf of the Annals of Botany Company.)

Bacteria can reduce toxic selenite into less toxic, elemental selenium (Se(0)), but the mechanism on how bacterial cells reduce selenite at molecular level is still not clear. We used Escherichia coli strain K12, a common bacterial strain, as a model to study its growth response to sodium selenite (Na2SeO3) treatment and then used quantitative real-time PCR (qRT-PCR) to quantify transcript levels of three E. coli selenopolypeptide genes and a set of machinery genes for selenocysteine (SeCys) biosynthesis and incorporation into polypeptides, whose involvements in the selenite reduction are largely unknown. We determined that 5 mM Na2SeO3 treatment inhibited growth by ∼ 50% while 0.001 to 0.01 mM treatments stimulated cell growth by ∼ 30%. Under 50% inhibitory or 30% stimulatory Na2SeO3 concentration, selenopolypeptide genes (fdnG, fdoG, and fdhF) whose products require SeCys but not SeCys biosynthesis machinery genes were found to be induced ≥2-fold. In addition, one sulfur (S) metabolic gene iscS and two previously reported selenite-responsive genes sodA and gutS were also induced ≥2-fold under 50% inhibitory concentration. Our findings provide insight about the detoxification of selenite in E. coli via induction of these genes involved in the selenite reduction process.