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Paeonia ostii is an emerging woody oil crop, but drought severely inhibits its growth and promotion in arid or semiarid areas, and little is known about the mechanism governing this inhibition. In this study, the full-length cDNA of a caffeoyl-CoA O-methyltransferase gene (CCoAOMT) from P. ostii was isolated, and determined to be comprised of 987 bp. PoCCoAOMT encoded a 247-amino acid protein, which was located in the nucleus and cytosol. Significantly higher PoCCoAOMT transcription was detected in P. ostii treated with drought stress. Subsequently, the constitutive overexpression of PoCCoAOMT in tobacco significantly conferred drought stress tolerance. Under drought stress, transgenic lines exhibited lower reactive oxygen species (ROS) accumulation, and higher antioxidant enzyme activities and photosynthesis. Moreover, the expression levels of senescence-associated genes were significantly downregulated, whereas the expression levels of lignin biosynthetic genes and PoCCoAOMT were significantly upregulated in transgenic lines. Similarly, transgenic lines produced significantly higher lignin, especially guaiacyl-lignin. These results suggest that PoCCoAOMT is a vital gene in promoting lignin synthesis and ROS scavenging to confer drought stress tolerance in P. ostii., (Copyright © 2020 Elsevier B.V. All rights reserved.)

SUMMARY: Drought is a detrimental environmental factor that restricts plant growth and threatens food security throughout the world. WRKY transcription factors play vital roles in abiotic stress response. However, the roles of IIe subgroup members from WRKY transcription factor family in soluble sugar mediated drought response are largely elusive. In this study, we identified a drought‐responsive IIe subgroup WRKY transcription factor, PoWRKY69, from Paeonia ostii. PoWRKY69 functioned as a positive regulator in response to drought stress with nucleus expression and transcriptional activation activity. Silencing of PoWRKY69 increased plants sensitivity to drought stress, whereas conversely, overexpression of PoWRKY69 enhanced drought tolerance in plants. As revealed by yeast one‐hybrid, electrophoretic mobility shift assay, and luciferase reporter assays, PoWRKY69 could directly bind to the W‐box element of fructose‐1,6‐bisphosphate aldolase 5 (PoFBA5) promoter, contributing to a cascade regulatory network to activate PoFBA5 expression. Furthermore, virus‐induced gene silencing and overexpression assays demonstrated that PoFBA5 functioned positively in response to drought stress by accumulating fructose to alleviate membrane lipid peroxidation and activate antioxidant defense system, these changes resulted in reactive oxygen species scavenging. According to yeast two‐hybrid, bimolecular fluorescence complementation, and firefly luciferase complementation imaging assays, valine‐glutamine 11 (PoVQ11) physically interacted with PoWRKY69 and led to an enhanced activation of PoWRKY69 on PoFBA5 promoter activity. This study broadens our understanding of WRKY69‐VQ11 module regulated fructose accumulation in response to drought stress and provides feasible molecular measures to create novel drought‐tolerant germplasm of P. ostii. Significance Statement: This manuscript identified a novel WRKY69‐VQ11 module that regulated fructose accumulation in response to drought stress, which provides feasible molecular measures to create novel drought‐tolerant germplasm of Paeonia ostii. [ABSTRACT FROM AUTHOR]

With persistent elevation in global temperature, water scarcity becomes a major threat to plant growth and development, yield security, agricultural sustainability, and food production. Proline, as a key osmolyte and antioxidant, plays a critical role in regulating drought tolerance in plants, especially its key biosynthetic enzyme, delta-1-pyrroline-5-carboxylate synthase (P5CS), which always positively responds to drought stress. As an important woody oil crop, the expansion of Paeonia ostii cultivation needs to address the issue of plant drought tolerance. Here, we isolated a PoP5CS gene from P. ostii, with an open reading frame of 1842 bp encoding 613 amino acids. PoP5CS expression progressively increased in response to increasing drought stress, and it was localized in the cytoplasm. Silencing of PoP5CS in P. ostii reduced drought tolerance, accompanied by decreased proline content, elevated reactive oxygen species (ROS) accumulation, and increased relative electrical conductivity (REC) and malondialdehyde (MDA) levels. Conversely, overexpression of PoP5CS in Nicotiana tabacum plants enhanced drought resistance, manifested by increased proline levels, reduced ROS accumulation, and lower REC and MDA contents. This study isolates PoP5CS from P. ostii and validates its role in regulating drought tolerance, providing valuable genetic resources and theoretical insights for the development of drought-resistant P. ostii cultivars. [ABSTRACT FROM AUTHOR]

Drought is a detrimental environmental factor limiting sustainable agricultural development worldwide. Paeonia ostii , an oil-producing woody crop, while its endogenous mystery underlying this tolerance remains largely elusive to scholars. Herein, we reported that PoWRKY17, a WRKY transcription factor from IId subgroup, positively functioned in face of drought stress in P. ostii. PoWRKY17 expressed in significantly higher abundance when drought was applied. Silencing of PoWRKY17 substantially reduced drought resistance, with decreased leaf water content and protective enzyme activities, increased relative electric conductivity (REC), malondialdehyde (MDA) content, and reactive oxygen species (ROS) accumulation. On the contrary, overexpression of PoWRKY17 endowed plants with higher drought tolerance with opposite drought-relevant physiological indices. Notably, both PoWRKY17- silenced P. ostii and PoWRKY17- overexpressing plants showed changes in lignin content under drought stress. Based on this clue, we quantified the expression of lignin biosynthetic caffeoyl-CoA O -methyltransferase (CCoAOMT) gene in PoWRKY17 -silenced P. ostii and found that PoCCoAOMT expression was significantly repressed. Next, protein-gene interaction assays showed that PoWRKY17 interacted with PoCCoAOMT promoter by targeting the W-box element and activated PoCCoAOMT expression under drought stress, which has been early verified to act as a positive participant in P. ostii drought tolerance. This study broadens our understanding of WRKY-mediated lignin biosynthesis regulation in response to drought stress in plants. [Display omitted] • A drought-related WRKY transcription factor PoWRKY17 was identified in Paeonia ostii. • PoWRKY17 positively responded to drought stress with enhanced expression. • PoWRKY17 enhanced drought tolerance in plants by promoting lignin accumulation. • PoWRKY17 enhanced PoCCoAOMT expression by targeting the W-box element. [ABSTRACT FROM AUTHOR]