Identificación y caracterización funcional del complejo nuclear de proteínas LSM de Arabidopsis thaliana en la respuesta de aclimatación a las temperaturas bajas

Abstract

Living organisms are exposed to changes in their environment that can affect their development and reproduction. Plants, as sessile organisms, have developed mechanisms to cope with unfavorable environmental alterations. Low temperatures are among the factors that constraint their geographical distribution and can cause great economic losses. Species from temperate regions have evolved an adaptive response, named cold acclimation, so they can increase their constitutive freezing tolerance after exposure to low, nonfreezing temperatures (Levitt, 1980). Cold acclimation is a complex process during which many molecular and physiological changes take place, such as alterations in lipid composition, and increase in cytosolic calcium, abscisic acid (ABA), sugars and other osmolytes, among others (Salinas, 2002; Theocharis y col., 2012). In a general and simply way, the adaptive process begins with the sensing of low temperature by unknown receptors that transmit the signal inside the cell (Knight y Knight, 2012). In the cytoplasm, the signal is transduced and activates transcriptional factors that control gene expression (Huang y col., 2012). The coldregulated gene products, in a direct or indirect way, control the physiological changes that allow plants to increase freezing tolerance (Theocharis y col., 2012). Changes in gene expression are one of the mayor alterations that take place during cold acclimation, and much research has been conducted to elucidate how they are controled. Although coldregulated gene expression is tightly regulated at the transcriptional level, recent works have revealed that it is also under post-transcriptional, translational and post-translational control (Viswanathan y Zhu, 2002; Barrero-Gil y Salinas, 2013). The SM-LIKE (LSM) proteins constitute a large family of proteins involved in multiple aspects of RNA metabolism. In humans and yeast, there are eight highly conserved LSM proteins (LSM1 to LSM8) that form two different heptameric ring complexes, LSM1- LSM7 and LSM2-LSM8, localized in the cytoplasm and nucleus, respectively. LSM1 and LSM8 define and confer specificity to each complex, while the other LSM proteins (LSM2 to LSM7) participates in both cytoplasmic and nuclear complexes (Beggs, 2005). The LSM1-LSM7 cytoplasmic complex binds to oligoadenilated mRNAs, promoting their degradation. The LSM2-LSM8 nuclear complex binds to and stabilizes the U6 small nuclear RNA (U6 snRNA) in order to build the U6 small nuclear ribonucleoprotein (U6snRNP) and the core of the spliceosome, and functions in pre-mRNA splicing (Beggs, 2005). In silico studies identified potential homologs for all the LSM proteins in Arabidopsis, three of them being duplicated (LSM1, LSM3 and LSM6) (Wang y Brendel, 2004). To date, however, plant LSMs have nor been functionally characterized, and their role in RNA metabolism remains to be elucidated. Only Arabidopsis LSM5 and LSM4 genes have been experimentally studied, both of them being related to abscisic acid and osmotic stress signaling (Xiong y col., 2001b; Zhang y col., 2011). Previous work in our laboratory isolated a novel cold-inducible gene, RCI6, encoding a yeast and human LSM2 homolog. Besides RCI6/LSM2, all Arabidopsis LSM genes are coldinducible suggesting a function of LSM complexes in the regulation of cold acclimation in Arabidopsis. Therefore, the main objetives of this work were: • The functional characterization of Arabidopsis LSM2-LSM8 complex • The elucidation of the role of Arabidopsis LSM2-LSM8 complex in cold acclimation