Abstract
Stress granules (SGs), which are formed in the plant cytoplasm under stress conditions, are transient dynamic sites (particles) for mRNA storage. SGs are actively involved in protecting mRNAs from degradation. Oligouridylate binding protein 1b (UBP1b) is a component of SGs. The formation of microscopically visible cytoplasmic foci, referred to as UBP1b SG, was induced by heat treatment in UBP1b-overexpressing Arabidopsis plants (UBP1b-ox). A detailed understanding of the function of UBP1b, however, is still not clear. UBP1b-ox plants displayed increased heat tolerance, relative to control plants, while ubp1b mutants were more sensitive to heat stress than control plants. Microarray analysis identified 117 genes whose expression was heat-inducible and higher in the UBP1b-ox plants. RNA decay analysis was performed using cordycepin, a transcriptional inhibitor. In order to determine if those genes serve as targets of UBP1b, the rate of RNA degradation of a DnaJ heat shock protein and a stress-associated protein (AtSAP3) in UBP1b-ox plants was slower than in control plants; indicating that the mRNAs of these genes were protected within the UBP1b SG granule. Collectively, these data demonstrate that UBP1b plays an integral role in heat stress tolerance in plants.
Highlights
Plants are strongly affected in a negative manner by adverse environmental stress conditions, such as high temperature, cold weather, drought, and high salinity
Previous observations indicated that stress granules (SGs) are formed in response to heat stress and that UBP1b is localized within the SGs (Weber et al, 2008)
In relative comparison to the intensity of the signals observed when UBP1b-ox plants were subjected to a severe heat stress (40◦C), these cytoplasmic foci of UBP1b signals in the UBP1b-ox plants were weaker and less abundant when plants were subjected to a mild heat stress (37◦C) (Figure 1C)
Summary
Plants are strongly affected in a negative manner by adverse environmental stress conditions, such as high temperature, cold weather, drought, and high salinity. The regulation of mRNA, including mRNA degradation and stabilization, is one of the mechanisms used by plants to effectively adapt to abiotic stress (Nakaminami et al, 2012). Several types of particles exist in the cytoplasm of plants, such as stress granules (SGs; Kedersha et al, 1999) and processing bodies (P-bodies), that contribute to mRNA regulation (Bashkirov et al, 1997; Gibbings et al, 2009). P-bodies are involved in mRNA degradation, while SGs are involved in mRNA stabilization. SGs form in the cytosol when cells are exposed to stress conditions (Nover et al, 1983; Kayali et al, 2005). A major function of SG is to protect RNAs from adverse conditions within the cell that result
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