Abstract
Seedling-lethal phenotypes of Arabidopsis (Arabidopsis thaliana) mutants that are defective in early steps in the sterol biosynthetic pathway are not rescued by the exogenous application of brassinosteroids. The detailed molecular and physiological mechanisms of seedling lethality have yet to be understood. Thus, to elucidate the underlying mechanism of lethality, we analyzed transcriptome and proteome profiles of the cyp51A2 mutant that is defective in sterol 14alpha-demethylation. Results revealed that the expression levels of genes involved in ethylene biosynthesis/signaling and detoxification of reactive oxygen species (ROS) increased in the mutant compared with the wild type and, thereby, that the endogenous ethylene level also increased in the mutant. Consistently, the seedling-lethal phenotype of the cyp51A2 mutant was partly attenuated by the inhibition of ethylene biosynthesis or signaling. However, photosynthesis-related genes including Rubisco large subunit, chlorophyll a/b-binding protein, and components of photosystems were transcriptionally and/or translationally down-regulated in the mutant, accompanied by the transformation of chloroplasts into gerontoplasts and a reduction in both chlorophyll contents and photosynthetic activity. These characteristics observed in the cyp51A2 mutant resemble those of leaf senescence. Nitroblue tetrazolium staining data revealed that the mutant was under oxidative stress due to the accumulation of ROS, a key factor controlling both programmed cell death and ethylene production. Our results suggest that changes in membrane sterol contents and composition in the cyp51A2 mutant trigger the generation of ROS and ethylene and eventually induce premature seedling senescence.
Highlights
Seedling-lethal phenotypes of Arabidopsis (Arabidopsis thaliana) mutants that are defective in early steps in the sterol biosynthetic pathway are not rescued by the exogenous application of brassinosteroids
According to our previous results (Kim et al, 2005), the Arabidopsis cyp51A2 mutant that was defective in the 14a-demethylation step of the sterol biosynthetic pathway displayed a seedling-lethal phenotype with reduced cell elongation
Our microarray data revealed that the expression of sterols and BR biosynthetic genes was increased in the cyp51A2 mutant (Table I; i.e., a homolog of sterol-C5desaturase [HDF7], C-22 sterol desaturase [CYP710A4], steroid 22a-hydroxylase [DWF4], and BR-6 oxidase [CYP85A1 and CYP85A2])
Summary
Seedling-lethal phenotypes of Arabidopsis (Arabidopsis thaliana) mutants that are defective in early steps in the sterol biosynthetic pathway are not rescued by the exogenous application of brassinosteroids. Seedling Lethality by Ethylene and ROS in the cyp51A2 Mutant in cellulose biosynthesis during cell wall formation (Peng et al, 2002; Schrick et al, 2004) In addition to their structural function as membrane components and their role as biosynthetic precursors, sterols have been known to play various regulatory functions in biological systems. The StART domain was found in the homeodomain HD-ZIP family of putative transcription factors, including PHABULOSA (ATHB14) and GLABRA2, which are involved in leaf morphogenesis and trichome and root hair development, respectively (Ponting and Aravind, 1999; Schrick et al, 2004) He et al (2003) showed that sterols affect the expression of genes involved in cell expansion and cell division. The transcription of a number of genes has been shown to be activated in response to exogenous cholesterol treatments in animal systems (Edwards and Ericsson, 1999), indicating that sterols could perform common regulatory functions in both animal and plant development
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
