New Insights into the Roles of Osmanthus Fragrans Heat-Shock Transcription Factors in Cold and Other Stress Responses

Abstract

Sweet osmanthus (Osmanthus fragrans) is an evergreen woody plant that emits a floral aroma and is widely used in the landscape and fragrance industries. However, its application and cultivation regions are limited by cold stress. Heat-shock transcription factor (HSF) family members are widely present in plants and participate in, and regulate, the defense processes of plants under various abiotic stress conditions, but now, the role of this family in the responses of O. fragrans to cold stress is still not clear. Here, 46 OfHSF members were identified in the O. fragrans genome and divided into three subfamilies on the basis of a phylogenetic analysis. The promoter regions of most OfHSFs contained many cis-acting elements involved in multiple hormonal and abiotic stresses. RNA-seq data revealed that most of OfHSF genes were differentially expressed in various tissues, and some OfHSF members were induced by cold stress. The qRT-PCR analysis identified four OfHSFs that were induced by both cold and heat stresses, in which OfHSF11 and OfHSF43 had contrary expression trends under cold stress conditions and their expression patterns both showed recovery tendencies after the cold stress. OfHSF11 and OfHSF43 localized to the nuclei and their expression patterns were also induced under multiple abiotic stresses and hormonal treatments, indicating that they play critical roles in responses to multiple stresses. Furthermore, after a cold treatment, transient expression revealed that the malondialdehyde (MDA) content of OfHSF11-transformed tobacco significantly increased, and the expression levels of cold-response regulatory gene NbDREB3, cold response gene NbLEA5 and ROS detoxification gene NbCAT were significantly inhibited, implying that OfHSF11 is a negative regulator of cold responses in O. fragrans. Our study contributes to the further functional characterization of OfHSFs and will be useful in developing improved cold-tolerant cultivars of O. fragrans.

Genome-Wide Analysis of ZAT Gene Family in Osmanthus fragrans and the Function Exploration of OfZAT35 in Cold Stress

“…Before application of abiotic treatments, seedlings with good development and consistent growth were selected and transferred to the growth chamber for one week. For cold treatment, the growth chamber temperature was adjusted to 4 °C, while other parameters were maintained [ 9 ]. During the cold treatment, we set seven timepoints (0, 3, 12, 24, 72, and 120 h during cold treatment, and after recovery 72 h) to collect the first two leaf pairs from seedlings as samples, and each timepoint set three biological replicates.…”

“…The genes of the bHLH transcription factor (TF) in O. fragrans induced by cold stress were screened through quantitative real-time PCR (qRT-PCR), while the functions of the NAC TF family in response to cold stress in O. fragrans were also screened using qRT-PCR [ 7 , 8 ]. The overexpression of an O. fragrans heat shock factor OfHSF11 in tobacco ( Nicotiana benthamiana ) under cold stress could negatively impact transgenic plant responses to cold treatment [ 9 ]. However, the molecular mechanism of sweet osmanthus response to low temperature stress is still unclear.…”

“…In this study, the published genome-wide sequence and transcriptome of O. fragrans were screened to characterize the ZAT gene family and to explore their expression profiles in various organs or tissues and under cold and salt stresses [ 4 , 9 , 32 ]. As a result, 38 ZAT genes were identified.…”

Salt Tolerance Evaluation of Cucumber Germplasm under Sodium Chloride Stress

“…Additionally, the stem thickness and plant height of cucumber seedlings are significantly decreased [ 23 ]. NaCl stress also induces membrane peroxidation in cucumber seedlings, which significantly increases the permeability of the cell membrane, damages the cell membrane structure, and increases malondialdehyde (MDA) in leaves [ 24 ].…”

“…Salt stress alters membrane lipid content and lipid biosynthesis pathways in the plasma membrane and tonoplast [ 23 ], and the membrane permeability directly reflects the degree of membrane injury; hence, the malondialdehyde (MDA) content indirectly indicates the degree of membrane damage [ 24 ]. Proline together with glycine betaine osmotically balance and protect leaves from oxidative stress [ 29 ].…”