Cheng Q, Zhou Y, Liu Z, Zhang L, Song G, Guo Z, Wang W, Qu X, Zhu Y, Yang D
State Key Laboratory of Hybrid Rice, Engineering Research Center for Plant Biotechnology and Germplasm Utilization, Ministry of Education, College of Life Sciences, Wuhan University, Wuhan, China.
Plant Biol (Stuttg). 2015 Mar;17(2):419-29. doi: 10.1111/plb.12267. Epub 2015 Jan 7.
As sessile organisms, plants have evolved a wide range of defence pathways to cope with environmental stress such as heat shock. However, the molecular mechanism of these defence pathways remains unclear in rice. In this study, we found that OsHSFA2d, a heat shock transcriptional factor, encodes two main splice variant proteins, OsHSFA2dI and OsHSFA2dII in rice. Under normal conditions, OsHSFA2dII is the dominant but transcriptionally inactive spliced form. However, when the plant suffers heat stress, OsHSFA2d is alternatively spliced into a transcriptionally active form, OsHSFA2dI, which participates in the heat stress response (HSR). Further study found that this alternative splicing was induced by heat shock rather than photoperiod. We found that OsHSFA2dI is localised to the nucleus, whereas OsHSFA2dII is localised to the nucleus and cytoplasm. Moreover, expression of the unfolded protein response (UNFOLDED PROTEIN RESPONSE) sensors, OsIRE1, OsbZIP39/OsbZIP60 and the UNFOLDED PROTEIN RESPONSE marker OsBiP1, was up-regulated. Interestingly, OsbZIP50 was also alternatively spliced under heat stress, indicating that UNFOLDED PROTEIN RESPONSE signalling pathways were activated by heat stress to re-establish cellular protein homeostasis. We further demonstrated that OsHSFA2dI participated in the unfolded protein response by regulating expression of OsBiP1.
作为固着生物，植物进化出了广泛的防御途径来应对诸如热激等环境胁迫。然而，这些防御途径在水稻中的分子机制仍不清楚。在本研究中，我们发现水稻中的热激转录因子OsHSFA2d编码两种主要的剪接变体蛋白，即OsHSFA2dI和OsHSFA2dII。在正常条件下，OsHSFA2dII是占主导地位但转录无活性的剪接形式。然而，当植物遭受热胁迫时，OsHSFA2d被可变剪接为转录活性形式OsHSFA2dI，其参与热胁迫反应（HSR）。进一步研究发现，这种可变剪接是由热激而非光周期诱导的。我们发现OsHSFA2dI定位于细胞核，而OsHSFA2dII定位于细胞核和细胞质。此外，未折叠蛋白反应（UNFOLDED PROTEIN RESPONSE）传感器OsIRE1、OsbZIP39/OsbZIP60以及未折叠蛋白反应标记物OsBiP1的表达上调。有趣的是，OsbZIP50在热胁迫下也发生了可变剪接，这表明未折叠蛋白反应信号通路被热胁迫激活以重新建立细胞蛋白质稳态。我们进一步证明OsHSFA2dI通过调节OsBiP1的表达参与未折叠蛋白反应。
