Abstract
Variegated ‘Marble Queen’ (Epipremnum aureum) plant has white (VMW) and green (VMG) sectors within the same leaf. The white sector cells containing undifferentiated chloroplasts are viable, but the underlying mechanism for their survival and whether these white cells would use any metabolites as signal molecules to communicate with the nucleus for maintaining their viability remain unclear. We analyzed and compared phytohormone levels with their precursors produced in chloroplasts between VMW and VMG, and further compared their transcriptomes to understand the consequences related to the observed elevated 12-oxo phytodienoic acid (OPDA), which was 9-fold higher in VMW than VMG. Transcriptomic study showed that a large group of OPDA-responsive genes (ORGs) were differentially expressed in VMW, including stress-related transcription factors and genes for reactive oxygen species (ROS) scavengers, DNA replication and repair, and protein chaperones. Induced expression of these ORGs could be verified in OPDA-treated green plants. Reduced level of ROS and higher levels of glutathione in VMW were further confirmed. Our results suggest that elevated OPDA or its related compounds are recruited by white cells as a signaling molecule(s) to up-regulate stress and scavenging activity related genes that leads to reduced ROS levels and provides survival advantages to the white cells.
Highlights
The chloroplast is a photosynthetic center for energy transfer and an essential organelle for generating important cellular molecules such as amino acids, fatty acids and carbohydrates as well as precursors of vitamins and phytohormones[1]
After comparing our differentially expressed genes (DEGs) with OPDA-responsive genes (ORGs) reported by Taki et al.[7], we found that a significant proportion (19%) of Arabidopsis ORGs with annotation were transcription factors
Further comparing DEGs, we found several groups of ORGs that were up-regulated in VMW (Tables 1 and 2), and that their differential expression could benefit the survival of white cells
Summary
The chloroplast is a photosynthetic center for energy transfer and an essential organelle for generating important cellular molecules such as amino acids, fatty acids and carbohydrates as well as precursors of vitamins and phytohormones[1]. The metabolites produced in the chloroplast that function as signaling molecules including reactive oxygen species (ROS)[3,4], sugars5,6, 12-oxo phytodienoic acid (OPDA) of the jasmonic acid (JA) biosynthesis pathway[7,8], tetrapyrrole intermediates of chlorophyll biosynthesis pathway[9] and methylerythritol cyclodiphosphate of the methylerythritol phosphate (MEP) pathway[10] as well as phytohormones derived from chloroplast-produced precursors, such as gibberellin (GA), abscisic acid (ABA), salicylic acid (SA) and JA11,12 Variegated plants, such as Arabidopsis im, var[1] and var[2] mutants, have been widely used for studying chloroplast development and cell communication between green and color defective sectors[13,14,15,16]. We established the transcriptome of ‘Marble Queen’[30], which could be used for molecular study
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