Yanxiao Niu, Jiaoteng Bai, Xinye Liu, +16, and Shuzhi Zheng.

PNAS Nov 2, 2022; 119 (45) e2206846119

https://doi.org/10.1073/pnas.2206846119

Significance

Understanding how plant cells sense and transduce heat signals has critical implications for improving plant heat tolerance. Here, we demonstrate that under heat stress, the phosphatase PP2AB′β dephosphorylates and stabilizes the histone deacetylase HDA9 in the cytoplasm. The nucleoporin HOS1 then translocates HDA9 into the nucleus, where the zinc-finger transcription factor YY1 helps recruit it to target genes to regulate gene expression via histone deacetylation. The cytoplasm-to-nucleus translocation of HDA9 in response to heat is conserved in wheat and rice. Thus, we identified a mechanism by which plant cells transduce heat signals from the cytoplasm to the nucleus and regulate gene expression, which could be used for crop improvement.

Abstract

Heat stress limits plant growth, development, and crop yield, but how plant cells precisely sense and transduce heat stress signals remains elusive. Here, we identified a conserved heat stress response mechanism to elucidate how heat stress signal is transmitted from the cytoplasm into the nucleus for epigenetic modifiers. We demonstrate that HISTONE DEACETYLASE 9 (HDA9) transduces heat signals from the cytoplasm to the nucleus to play a positive regulatory role in heat responses in Arabidopsis. Heat specifically induces HDA9 accumulation in the nucleus. Under heat stress, the phosphatase PP2AB′β directly interacts with and dephosphorylates HDA9 to protect HDA9 from 26S proteasome-mediated degradation, leading to the translocation of nonphosphorylated HDA9 to the nucleus. This heat-induced enrichment of HDA9 in the nucleus depends on the nucleoporin HOS1. In the nucleus, HDA9 binds and deacetylates the target genes related to signaling transduction and plant development to repress gene expression in a transcription factor YIN YANG 1–dependent and –independent manner, resulting in rebalance of plant development and heat response. Therefore, we uncover an HDA9-mediated positive regulatory module in the heat shock signal transduction pathway. More important, this cytoplasm-to-nucleus translocation of HDA9 in response to heat stress is conserved in wheat and rice, which confers the mechanism significant implication potential for crop breeding to cope with global climate warming.

See https://www.pnas.org/doi/full/10.1073/pnas.2206846119

Figure 1: HDA9 abundance specifically responds to heat in Arabidopsis. (A) Phenotypic analysis of Col, hda9, and the complementation line HDA9pro:HDA9-FLAG/hda9 grown at 22 °C or exposed to HS treatment. (B) Survival rates of seedlings shown in A. Each point represents an individual data point. Data are shown as mean ± SE from all seedlings. At least three independent biological replicates were performed (****P < 0.0001; ns, no significant difference; as determined by two-tailed Student’s t test). (C) Immunoblot analysis of HDA9-GFP abundance in crude cell extracts (total; Left) and cytosolic (cytoplasm; Middle) and nuclear (nucleus; Right) fractions from the HDA9pro:HDA9-GFP/hda9 complemented line under control (22 °C), 37 °C (0.5 h), 150 mM NaCl, or 50 μM ABA treatment and then subjected to immunoblot analysis with an anti-GFP antibody. Anti-tubulin and anti-histone H3 antibodies served as loading controls and fraction markers. The titration of control samples (loading 4×, 2×, 1×, and 0.5×) is shown in SI Appendix, Fig. S19A. The control samples in C are equivalent to 0.5× (total), 2× (cytoplasm), and 1× (nucleus) of the titration shown in SI Appendix, Fig. S19A. Three independent biological replicates are shown in Dataset S9. The signal can be compared with the experimental samples. At least three independent biological replicates were performed. (D) HDA9-GFP fluorescence from HDA9pro:HDA9-GFP/hda9 roots subjected to 37 °C HS treatment for the indicated time. Confocal images of GFP fluorescence (green; Upper) and propidium iodide (PI; red) merged with GFP fluorescence (Lower) are shown. (Scale bars, 50 μm.) (E) Relative fluorescence intensity of HDA9-GFP (background was subtracted), as analyzed by ImageJ. Thirty nuclei in the same field of view were observed and quantified. Data are shown as mean ± SE.