Abstract
ZFPs play important roles in many biological processes, including plant development, stress response, and phytohormone response. RanBP2-type zinc finger transcription factors have been characterized in animals and humans. However, their functions remain largely unknown in plants. In this study, we identified a RanBP2-type zinc finger protein gene (SlRBZ) in tomato. SlRBZ was constitutively expressed in roots, stems, leaves, flowers, and fruits. The SlRBZ-GFP fused protein was localized in the nucleus. Overexpression of SlRBZ resulted in chlorosis and dwarf phenotypes in tomato. Determination of physiological index showed that chlorophyll, carotenoid, and GAs contents were evidently decreased in transgenic plants. Furthermore, the qRT-PCR and RNA-Seq analyses demonstrated that the transcription of the genes involved in these biosynthesis pathways obviously decreased in SlRBZ-OE plants. In addition, ultrastructural observation by transmission electron microscopy indicated that plastids could not develop into mature chloroplasts with normal chloroplast membrane and thylakoid membrane system in SlRBZ-OE plants. The results suggest that overexpression of SlRBZ may impair the biosynthesis of chlorophyll, carotenoid, and gibberellin through blocking chloroplast development, resulting in chlorosis and dwarfism in tomato.
Highlights
Chlorophyll (Chl) has important function in light harvesting and photosynthetic energy transduction, which is closely related to chloroplast-nuclear signaling and chloroplast development (Eckhardt et al, 2004)
Ultrastructural observation revealed that chloroplast formation was blocked. This conclusion was further supported by RNASeq analyses and qRT-PCR. These results demonstrate that overexpression of SlRBZ may inhibit the biosynthesis of Chl, carotenoid, and GA through affecting chloroplast formation, resulting in chlorosis and dwarfism
A RanBP2 zinc finger protein gene was identified in upland cotton, which is expressed in the different development stages of glands (Chang et al, 2007)
Summary
Chlorophyll (Chl) has important function in light harvesting and photosynthetic energy transduction, which is closely related to chloroplast-nuclear signaling and chloroplast development (Eckhardt et al, 2004). Chl biosynthesis is a complex process, including the formation of 5aminolevulinic acid (ALA), protoporphyrin IX from eight molecules of ALA, and Chl in the magnesium branch (Beale, 1999; Eckhardt et al, 2004). Uroporphyrinogen III is oxidized into Proto under the function of protoporphyrinogen oxidase (Tanaka and Tanaka, 2007). Inhibition of each enzymatic step can affect the synthesis of Chl and result in leaf color change. The transcription of these enzymes required for Chl biosynthesis is individually and independently regulated. Chloroplasts are arrested and Chl is almost absent in the insertion mutant of the HST gene, which encodes an important enzyme participating in the biosynthesis of the PSII mobile electron transport co-factor PQ (Chao et al, 2014)
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