Mitochondrial retrograde regulation tuning fork in nuclear genes expressions of higher plants

In plant cells, there are three organelles： the nucleus, chloroplast, and mitochondria that store genetic information. The nucleus possesses the majority of genetic information and controls most aspects of organelles gene expression, growth, and development. In return, organelles also send signals back to regulate nuclear gene expression, a process defmed as retrograde regulation. The best studies of organelles to nucleus retrograde regulation exist in plant chloroplast-to-nuclear regulation and yeast mitochondria-to-nuclear regulation. In this review, we summarize the recent understanding of mitochondrial retrograde regulation in higher plant, which involves multiple potential signaling pathway in relation to cytoplasmic male-sterility, biotic stress, and abiotic stress. With respect to mitochondrial retrograde regulation signal pathways involved in cytoplasmic male-sterility, we consider that nuclear transcriptional factor genes are the targeted genes regulated by mitochondria to determine the abnormal reproductive development, and the MAPK signaling pathway may be involved in this regulation in Brassica juncea. When plants suffer biotic and abiotic stress, plant ceils will initiate cell death or other events directed toward recovering from stress. During this process, we propose that mitochondria may determine how plant cell responds to a given stress through retrograde regulation. Meanwhile, several transducer molecules have also been discussed here. In particular, the Paepe research group reported that leaf mitochondrial modulated whole cell redox homeostasis, set antioxidant capacity, and determined stress resistance through altered signaling and diurnal regulation, which is an indication of plant mitochondria with more active function than ever.

Anterograde and Retrograde Regulation of Nuclear Genes Encoding Mitochondrial Proteins during Growth, Development, and Stress

Mitochondrial biogenesis and function in plants require the expression of over 1000 nuclear genes encoding mitochondrial proteins （NGEMPs）. The expression of these genes is regulated by tissue-specific, developmental, internal, and external stimuli that result in a dynamic organelle involved in both metabolic and a variety of signaling processes. Although the metabolic and biosynthetic machinery of mitochondria is relatively well understood, the factors that regu- late these processes and the various signaling pathways involved are only beginning to be identified at a molecular level. The molecular components of anterograde （nuclear to mitochondrial） and retrograde （mitochondrial to nuclear） signaling pathways that regulate the expression of NGEMPs interact with chloroplast-, growth-, and stress-signaling pathways in the cell at a variety of levels, with common components involved in transmission and execution of these signals. This positions mitochondria as important hubs for signaling in the cell, not only in direct signaling of mitochondrial function per se, but also in sensing and/or integrating a variety of other internal and external signals. This integrates and optimizes growth with energy metabolism and stress responses, which is required in both photosynthetic and non-photosynthetic cells.