Overexpression of oligouridylate binding protein 1b results in ABA hypersensitivity

Oligouridylate binding protein 1b (UBP1b), a marker protein of plant stress granules (SGs), plays a role in heat stress tolerance in plants. A previous microarray analysis revealed that the expression of several ABA signaling-related genes is higher in <i>UBP1b</i>-overexpressing <i>Arabidopsis</i> plants (<i>UBP1b</i>-ox) subjected to both non-stressed and heat stress conditions. Root elongation and seed germination assays demonstrated that <i>UBP1b</i>-ox exhibited hypersensitivity to ABA. RT-qPCR analysis confirmed that mitogen-activated protein kinase (MAPK) cascade genes, such as <i>MPK3, MKK4</i>, and <i>MKK9</i> were upregulated in <i>UBP1b</i>-ox plants. ABA receptor genes, including <i>PYL5</i> and <i>PYL6</i>, were also upregulated in <i>UBP1b</i>-ox plants. mRNA of <i>WRKY33</i> – a downstream gene of MPK3 and an upstream gene of ethylene biosynthesis, exhibited high levels of accumulation, although the level of endogenous ABA was not significantly different between <i>UBP1b</i>-ox and control plants. In addition, RNA decay analysis revealed that <i>WRKY33</i> was more stable in <i>UBP1b</i>-ox plants, indicating that the mRNA of <i>WRKY33</i> was protected within UBP1b SGs. Collectively, these data demonstrate that UBP1b plays an important role in plant response to ABA.