SECRET AGENT, an Arabidopsis thaliana O-GlcNAc transferase, modifies the Plum pox virus capsid protein

The capsid protein of Plum pox virus (PPV-CP) is modified with O-linked GlcNAc (O-GlcNAc). While Arabidopsis has two O-GlcNAc transferases, SECRET AGENT (SEC) and SPINDLY (SPY), previous work suggests that SEC modifies PPV-CP and that the modification plays a role in the infection process. Here, we show that when co-expressed in Escherichia coli SEC modifies PPV-CP. Deletion mapping and site-directed mutagenesis identified three threonine and a serine located near the N-terminus of PPV-CP that are modified by SEC. Two of these threonines have recently been shown to be modified in virus from plants suggesting that SEC has the same specificity in plants and E. coli.     

SPINDLY与赤霉素的信号转导

SPINDLY(SPY)作为一负调节子参与GA的信号转导,34肽重复结构(TPR)与C-端区域对其正常功能都十分重要.SPy基因在植物中呈组成型表达,其蛋白主要出现在细胞核部位.SPY蛋白与动物中的氧连N-乙酰葡萄糖胺转移酶(OGT)具有广泛的同源性,两者可能有着类似的作用机制.本文主要介绍GA突变体、SPy基因、SPY蛋白及其在大麦中的同源物HvSPY的结构与功能相关方面的一些研究进展.     

The role of SPY and its TPR domain in the regulation of gibberellin action throughout the life cycle of Petunia hybrida plants

SPY acts as a negative regulator of gibberellin (GA) action in Arabidopsis, but its mode of action and regulation are still unknown. SPY over-expression in transgenic petunia plants affected various GA-regulated processes, including seed germination, shoot elongation, flower initiation, flower development and the expression of a GA-induced gene, GIP. A similar phenotype was obtained when wild-type petunia plants were treated with the GA-biosynthesis inhibitor, paclobutrazol. The N-terminus of SPY contains tetratricopeptide repeats (TPR). TPR motifs participate in protein-protein interactions, suggesting that SPY is part of a multiprotein complex. To test this hypothesis, we over-expressed the SPY's TPR region without the catalytic domain in transgenic petunia and generated a dominant-negative SPY mutant. The transgenic seeds were able to germinate on paclobutrazol, suggesting an enhanced GA signal. We cloned the petunia SPY homologue, PhSPY, and showed that its mRNA level is not affected by GA or ABA. The results of this study support the role of SPY as a negative regulator of GA action, suggest that the TPR domain is required for the interaction with other proteins to form an active complex and indicate that different plants use similar mechanisms to transduce the GA signal.     

Mapping of two O-GlcNAc modification sites in the capsid protein of the potyvirus Plum pox virus

A large number of O-linked N-acetylglucosamine (O-GlcNAc) residues have been mapped in vertebrate proteins, however targets of O-GlcNAcylation in plants still have not been characterized. We show here that O-GlcNAcylation of the N-terminal region of the capsid protein of Plum pox virus resembles that of animal proteins in introducing O-GlcNAc monomers. Thr-19 and Thr-24 were specifically O-GlcNAcylated. These residues are surrounded by amino acids typical of animal O-GlcNAc acceptor sites, suggesting that the specificity of O-GlcNAc transferases is conserved among plants and animals. In laboratory conditions, mutations preventing O-GlcNAcylation of Thr-19 and Thr-24 did not have noticeable effects on PPV competence to infect Prunus persicae or Nicotiana clevelandii. However, the fact that Thr-19 and Thr-24 are highly conserved among different PPV strains suggests that their O-GlcNAc modification could be relevant for efficient competitiveness in natural conditions.