Role of miRNAs in carbon metabolism and stress responses in Arabidopsis thailiana mitochondrial uncoupling protein mutants ucp1/2/3 and activation-tagged transcription factor allele PRODUCTION OF ANTHOCYANIN PIGMENT/PAP1-D/MYB75



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Texas Tech University


Plant sugars, specifically the transported disaccharide primary product of photosynthesis sucrose, control multiple aspects of the plant life cycle including structure, growth, and development. Notably, sucrose functions as a signaling molecule by unknown molecular mechanisms to facilitate various stress adaptations. Accumulation of high sugar concentrations in plants is a hallmark associated with many environmental stimuli, abiotic, and biotic stresses, resulting in accumulation of antioxidant secondary carbon metabolites anthocyanins and flavanoids. From a regulatory perspective, some microRNAs (miRNAs) are potentially components of sucrose signaling pathways because of their established roles in secondary carbon metabolism. However, current understanding of the role of miRNAs in sucrose signaling pathway is very scarce. In this study, I endeavored to uncover the effect of exogenous high sucrose stress on miRNA profiles in Arabidopsis mitochondrial uncoupling protein mutants (ucp) that are defective in reactive oxygen species (ROS) homeostasis and pap1-D, a positive effector transgene mutant of secondary metabolite anthocyanin pathway. My aim is to better understand the UCP protein roles in response to oxidative stress and subject to regulatory control by sugar signaling, and to ascertain the importance of miRNAs impacting primary metabolism and regulation of carbon partitioning to the secondary metabolite pathways antioxidant anthocyanins and flavanols. Qualitative measurements of ROS hydrogen peroxide and superoxide abundance with specific chromogenic stains showed higher endogenous ROS in sucrose-treated samples. My analysis of small RNA deep sequencing datasets from sucrose-treated mutant and wild-type seedlings shows that high exogenous sucrose treatment altered the expression of many miRNAs inferred to be involved in primary metabolism, stress responses, hormone and nutrient signaling pathways, secondary metabolism and vegetative and reproductive development. Moreover, messenger RNA transcriptomic datasets from the same experiments shows a substantial reduction of photosynthesis- related genes and an induction of the genes and regulatory transcription factors involved in flavonoid pathway which was further evidenced by a very high accumulation of anthocyanin in all genotypes, especially pap1-D/MYB75 overexpression which showed some genotype-by-sucrose interaction effects. My sRNA-/mRNA-seq systems approach revealed evidence of a retrograde signaling mechanism from UCP family member proteins in the mitochondrial inner membrane to the genome-wide reprogramming of gene expression for carbon partitioning pathways from primary to secondary antioxidant metabolites, including post-transcriptional control.



Sucrose, miRNA, UCP, Anthocyanin, pap1-D, ROS