Strain β-lactam Chemical Biological Activity tolerance to Arabidopsis, indicating the involvement of HDA15 in salt strain tolerance in these plants. We also examined the phenotype of hda15 ko mutants in response to salt strain, but these were comparable to that of Col-0. The cause for this may well be that HDA15 is 1 of many homologs belonging to class II of HDACs, which contains HDA5, HDA14, and HDA18. Only the quadruple mutant, hda5/14/15/18, showed a phenotype that was sensitive to salt strain (Ueda et al., 2017). Hence, the loss of function of HDA15 alone might not exert a phenotypic impact in response to salt tension on account of the compensatory function of other homologs. Furthermore, due to the fact HDA15 OE transgenic plants showed tolerant phenotypes against salt strain, we utilized Col-0 and HDA15 OE plants to characterize the function of HDA15. Previous research also proposed that overTopoisomerase Inhibitor Accession expression of AtHD2A and AtHD2D in Arabidopsis enhanced tolerance to salt stress (Sridha and Wu, 2006; Chen et al., 2010; Han et al., 2016; Zheng et al., 2016, 2019; Ueda et al., 2017). As HDA15 is involved in ABA signaling and ABA accumulation enhances salt stress tolerance (Sah et al., 2016; Lee and Search engine marketing, 2019), we examined the impact of salt anxiety on the transcript levels of ABA biosynthetic genes. NCEDs are enzymes that mediate ABA biosynthesis. To date, five NCED genes are known to be present in Arabidopsis. These involve AtNCED2, AtNCED3, AtNCED5, AtNCED6, and AtNCED9 (Ali et al., 2020). NCED3, which is induced by each ABA and NaCl, plays a important part in osmotic stress-induced ABA biosynthesis (Iuchi et al., 2000; Tan et al., 2003; Barrero et al., 2006). Moreover, overexpression of OsNCED3 in rice conferred protection against osmotic pressure (Huang et al., 2018). NCED3 induction enhanced ABA biosynthesis, resulting in enhanced ABA accumulation, which speeds up stomatal closure and upregulates the expression of stress-responsive genes, major to increased strain tolerance in plants (Jakab et al., 2005). Droughtrelated tension causes the histone methyltransferase, ATX1, to modify H3K4me3, which then activates NCED3, resulting in drought- and ABA-related genes getting upregulated (Kim et al., 2015). As shown in Arabidopsis, overexpression of GmWRKY16, a soybean WRKY TF, increases ABA accumulation, which is also observed when NCED3 is upregulated, enabling transgenic plants to resist drought and salt stresses (Ma et al., 2019). Therefore, upregulation of NCED3 in HDA15 OE plants might be a important issue in osmotic stress tolerance, with specific reference to salt tension. The elevated transcript levels of NCED3 led us to examine other downstream genes involved inside the ABA biosynthetic pathway. NCED genes catalyze the synthesis of xanthoxin, which can be converted to abscisic aldehyde by short-chain alcohol dehydrogenase/reductase (SDR/ABA2) and after that to ABA by abscisic aldehyde oxidase (AAO3). The molybdenum cofactor sulfurase/ABA3 is needed by aldehyde oxidase for its activity (Long et al., 2019). However, as ABA2, ABA3, and AAO3 play only minor roles in ABA biosynthetic pathway (Ma et al., 2018), their transcript levels weren’t substantially elevated in HDA15 OE plants (Figure 8). Also, the larger accumulation of ABA in HDA15 OE plants may perhaps be due to BG2 upregulation,Frontiers in Plant Science | www.frontiersin.orgApril 2021 | Volume 12 | ArticleTruong et al.HDA15 Function in Salt StressFIGURE 9 | The co-action of HDA15 and HY5 in response to salt pressure. Three-day-old plants germinated in standard MS medi.
