Abstract
Brassinosteroids (BRs) play an essential role in plant growth, development, and responses to diverse abiotic stresses. However, previous studies mainly analyzed how exogenous BRs influenced plant physiological reactions to drought stress, therefore, genetic evidences for the endogenous BRs-mediated regulation of plant responses still remain elusive. In this study, a key BRs biosynthetic gene, SoCYP85A1 was cloned from Spinacia oleracea, which has a complete open reading frame of 1,392 bp encoding a 464 amino acid peptide and shares high sequence similarities with CYP85A1 from other plants. The expression of SoCYP85A1 which was higher in leaf compared with root and stem, was induced by treatments of PEG6000, abscisic acid (ABA), low temperature and high salt. Increases in both SoCYP85A1 transcripts and endogenous BRs in transgenic tobacco which resulted in longer primary root and more lateral roots enhanced drought tolerance compared with wild types. The transgenic tobacco accumulated much lower levels of reactive oxygen species and malondialdehyde (MDA) than wild types did, accompanied by significantly higher content of proline and notably enhanced activities of antioxidant enzymes. Besides, transcriptional expressions of six stress-responsive genes were regulated to higher levels in transgenic lines under drought stress. Taken together, our results demonstrated that SoCYP85A1 involves in response to drought stress by promoting root development, scavenging ROS, and regulating expressions of stress-responsive genes.
Highlights
Abiotic stress such as drought, has been a primary factor adversely affecting plants quality and production in the natural environment (Farooq et al, 2009; Li et al, 2009)
Multiple alignments showed that the SoCYP85A1 protein presented a high sequence identify with other CYP85A1 proteins from Fagopyrum esculentum (BAO79854, 81%), Morus notabilis (XP_010099314, 80%), Arabidopsis thaliana (NP_851105, 80%), Medicago truncatula ((XP_013451102, 79%), Theobroma cacao (XP_007032850, 79%), Glycine soja (KHN08349, 78%), Nicotiana tabacum (NP_001312136, 78%) and Solanum lycopersicum
Our result showed that in the case of water loss, transcriptional level of NtLEA5 was obviously increased in L2 and L8 compared with that of wild type (WT), whereas that of NtERD10C changed slightly, which suggested that induction of a higher transcriptional level of NtLEA5 might be a more effective strategy to resist against drought stress in transgenic lines overexpressing SoCYP85A1
Summary
Abiotic stress such as drought, has been a primary factor adversely affecting plants quality and production in the natural environment (Farooq et al, 2009; Li et al, 2009). Brassinosteroids as one of the most important phytohormones involve in various physiological processes (Choudhary et al, 2012). In addition of their roles in plant growth and development (Hu et al, 2000; Arteca and Arteca, 2001; Yu et al, 2004), BRs have recently been implicated in response to abiotic stresses (Kagale et al, 2007; Xia et al, 2009; Chung et al, 2014; Li et al, 2016a). Applications of exogenous BRs to plants result in various physiological effects, including promotion of germination and cell elongation, differentiation of tracheary element, enhancement of photomorphogenesis, pollen fertility and stress resistance (Clouse and Sasse, 1998; Steber and McCourt, 2001)
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