Posttranslational modifications of proteins by small ubiquitin-like modifiers (SUMOs) regulate protein degradation and localization, protein-protein interaction, and transcriptional activity. SUMO E3 ligase functions are executed by SIZ1/SIZ2 and Mms21 in yeast, the PIAS family members RanBP2, and Pc2 in human. The Arabidopsis thaliana genome contains only one gene, SIZ1, that is orthologous to the yeast SIZ1/SIZ2. Here, we show that Arabidopsis SIZ1 is expressed in all plant tissues. Compared with the wild type, the null mutant siz1-3 is smaller in stature because of reduced expression of genes involved in brassinosteroid biosynthesis and signaling. Drought stress induces the accumulation of SUMO-protein conjugates, which is in part dependent on SIZ1 but not on abscisic acid (ABA). Mutant plants of siz1-3 have significantly lower tolerance to drought stress. A genome-wide expression analysis identified ;1700 Arabidopsis genes that are induced by drought, with SIZ1 mediating the expression of 300 of them by a pathway independent of DREB2A and ABA. SIZ1-dependent, drought-responsive genes include those encoding enzymes of the anthocyanin synthesis pathway and jasmonate response. From these results, we conclude that SIZ1 regulates Arabidopsis growth and that this SUMO E3 ligase plays a role in drought stress response likely through the regulation of gene expression.

Certain plants increase their freezing tolerance in response to low nonfreezing temperatures, an adaptive process named cold acclimation. Light has been shown to be required for full cold acclimation, although how light and cold signals integrate and cross-talk to enhance freezing tolerance still remains poorly understood. Here, we show that HY5 levels are regulated by low temperature transcriptionally, via a CBF-and ABA-independent pathway, and posttranslationally, via protein stabilization through nuclear depletion of COP1. Furthermore, we demonstrate that HY5 positively regulates cold-induced gene expression through the Z-box and other cisacting elements, ensuring the complete development of cold acclimation. These findings uncover unexpected functions for HY5, COP1, and the Z-box in Arabidopsis response to low temperature, provide insights on how cold and light signals integrate to optimize plant survival under freezing temperatures, and reveal the complexity of the molecular mechanisms plants have evolved to respond and adapt to their fluctuating natural environment.

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The packaging industry has dramatically increased the number of packaging systems and designs made of plastics over recent decades. Plastics, in contrast with more traditional packaging materials such as glass and metals, are permeable systems that permit the exchange of low molecular weight compounds, e.g. gases and vapours, between the inner and the outer atmosphere. Despite this drawback, the availability of shapes and forms in which they can be manufactured, their ease of processing and handling, low price, excellent chemical resistance, etc., have made them very attractive in many packaging elds. Consequently, much industrial and academic research has been devoted to understanding the mechanisms of mass transport in polymers, to enable design of materials with improved barrier properties. The present paper reviews some of these developments, and highlights the structural factors that cause polymers to behave as high barrier materials, taking as benchmark the properties of one of the most widely used family of high barrier materials, the ethylene -vinyl alcohol copolymers.MST/5992