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Calcium signaling triggers early high humidity responses in Arabidopsis thaliana
Tuesday, 2024/12/24 | 07:53:40
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Saad Hussain, Hiraku Suda, Christine H. Nguyen, Dawei Yan, Masatsugu Toyota, Keiko Yoshioka, and Eiji Nambara PNAS; December 11, 2024; 121 (51) e2416270121; https://doi.org/10.1073/pnas.2416270121 SignificancePlants respond to increased humidity by altering their growth and physiology. Abscisic acid (ABA) plays a crucial role in plant humidity responses by regulating plant water status, primarily through stomatal control. However, the molecular mechanism for this response, especially early high humidity (HH) signaling, is incompletely understood. In this work, we report that HH rapidly increases cytosolic calcium concentrations in leaves within a few minutes of exposure to HH. This response requires CNGC2 and CNGC4 calcium channels, which activate calcium signaling to induce the expression of CYP707A3, encoding an ABA catabolic enzyme. AbstractPlants need to adapt to fluctuating atmospheric humidity and respond to both high and low humidity. Despite our substantial understanding of plant responses to low humidity, molecular mechanisms underlying the high humidity (HH) response are much less well understood. In this study, we investigated early responses to HH in Arabidopsis. Expression of CYP707A3, encoding an abscisic acid (ABA) 8′-hydroxylase, is induced by HH within 10 min, which leads to a decrease in foliar ABA level. We identified that the combined action of CAMTA3 and CAMTA2 transcription factors regulate this response. This regulation requires a calmodulin (CaM)-binding domain of CAMTA3. Transcriptomes of HH-regulated genes are enriched in those related to calcium signaling, including cyclic nucleotide-gated ion channels (CNGCs). Moreover, HH induces CNGC2- and CNGC4-mediated increases in cytosolic Ca2+ concentrations in leaves within a few minutes. We also found that CNGC2, CNGC4, and CAMTAs participate in HH-induced hyponastic movement of petioles. Taken together, our results indicate that CNGC2/CNGC4-Ca2+-CaM-CAMTA3/CAMTA2 acts as a primary regulatory module to trigger downstream HH responses.
See https://www.pnas.org/doi/10.1073/pnas.2416270121
Figure 1: Identification of transcription factor(s) responsible for early HH response. (A) A schematic diagram of transcription factor-binding sites listed in DAP-seq data (Top). Diagram of CYP707A3pro::GUS constructs (Bottom). (B) Quantification of ABA levels in transcription factor mutants before and after 1 h of HH treatment on 18-d-old plants. Means are shown with SE (n = 4~6). Dots represent biological replicates. Data were analyzed by two-way ANOVA with Tukey’s HSD. Different letters indicate significant differences (P < 0.05). (C) HH-induced GUS reporter expression driven by truncated CYP707A3 promoters. From Top to Bottom, reporter lines with 2.17-kb, 2.25-kb, and 2.76-kb promoters. Left panels (0 h) and Right panels (1 h) represent reporter lines before and after HH treatments, respectively. Scale bars indicate 0.5 cm.
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