The structure of Arabidopsis thaliana OST1 provides insights into the kinase regulation mechanism in response to osmotic stress

SnRK [SNF1 (sucrose non-fermenting-1)-related protein kinase] 2.6 [open stomata 1 (OST1)] is well characterized at molecular and physiological levels to control stomata closure in response to water-deficit stress. OST1 is a member of a family of 10 protein kinases from Arabidopsis thaliana (SnRK2) that integrates abscisic acid (ABA)-dependent and ABA-independent signals to coordinate the cell response to osmotic stress. A subgroup of protein phosphatases type 2C binds OST1 and keeps the kinase dephosphorylated and inactive. Activation of OST1 relies on the ABA-dependent inhibition of the protein phosphatases type 2C and the subsequent self-phosphorylation of the kinase. The OST1 ABA-independent activation depends on a short sequence motif that is conserved among all the members of the SnRK2 family. However, little is known about the molecular mechanism underlying this regulation. The crystallographic structure of OST1 shows that ABA-independent regulation motif stabilizes the conformation of the kinase catalytically essential α C helix, and it provides the basis of the ABA-independent regulation mechanism for the SnRK2 family of protein kinases.     

The Douglas-fir BiP promoter is functional in Arabidopsis and responds to wounding

A DNA sequence representing the promoter region of the Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) luminal binding protein PmBiP (PmBiPPro1) was isolated using inverse polymerase chain reaction (iPCR). Transient expression analysis of PmBiPPro1 fused to the beta-glucuronidase (GUS) reporter gene demonstrated that this promoter is functional in germinating Douglas-fir embryos. Transgenic Arabidopsis plants containing PmBiPPro1:GUS reporter gene constructs revealed strong staining associated with actively dividing/expanding cells and secretory tissues in developing seedlings. Wounding of cotyledons resulted in an increase in local staining associated with cells surrounding the wound site. Deletion analysis showed that elements necessary for basal-level expression reside within a -261 to +16 bp region, although upstream elements are necessary for higher-level expression in germinating Douglas-fir embryos, developing Arabidopsis seedlings and wounded cotyledons. Correlation of the observed expression pattern with the known function of BiP suggests that pathways controlling expression are highly conserved between angiosperms and gymnosperms.     

Effect of VTE1 AND VTE4 gene inactivation on salt stress response in Arabidopsis thaliana

The effect of inactivation of VTE1 and VTE4 genes, encoding enzymes involved in tocopherol biosynthesis, on concentrations of chlorophylls, carotenoids, anthocyanins and activity of catalase and guaiacol peroxidase in Arabidopsis thaliana under salt stress conditions were studied. It was shown, that the inactivation of the VTE4 gene in A. thaliana caused the decrease in concentrations of chlorophylls and carotenoids, and at the same time, inactivation of VTE1 gene resulted in 3.6-fold increase of catalase activity in comparison with the wild type. Under salt stress, the activities of guaiacol peroxidase increased in all investigated plant groups, while the concentrations of carotenoids increased only in the wild type and vte4 mutant line of A. thaliana. Salt stress did not change the concentrations of protein carbonyl groups and activities of catalase.     

A latitudinal cline and response to vernalization in leaf angle and morphology in Arabidopsis thaliana (Brassicaceae)

Adaptation to latitudinal patterns of environmental variation is predicted to result in clinal variation in leaf traits. Therefore, this study tested for geographic differentiation and plastic responses to vernalization in leaf angle and leaf morphology in Arabidopsis thaliana. Twenty-one European ecotypes were grown in a common growth chamber environment. Replicates of each ecotype were exposed to one of four treatments: 0, 10, 20 or 30 d of vernalization. Ecotypes from lower latitudes had more erect leaves, as predicted from functional arguments about selection to maximize photosynthesis. Lower-latitude ecotypes also had more elongated petioles as predicted by a biomechanical constraint hypothesis. In addition, extended vernalization resulted in shorter and more erect leaves. As predicted by functional and adaptive hypotheses, our results show genetically based clinal variation as well as environmentally induced variation in leaf traits.