Target of Rapamycin (TOR) is a major nutrition and energy sensor that regulates growth and life span in yeast and animals. In plants, growth and life span are intertwined not only with nutrient acquisition from the soil and nutrition generation via photosynthesis but also with their unique modes of development and differentiation. How TOR functions in these processes has not yet been determined. To gain further insights, rapamycin-sensitive transgenic Arabidopsis thaliana lines (BP12) expressing yeast FK506 Binding Protein12 were developed. Inhibition of TOR in BP12 plants by rapamycin resulted in slower overall root, leaf, and shoot growth and development leading to poor nutrient uptake and light energy utilization. Experimental limitation of nutrient availability and light energy supply in wild-type Arabidopsis produced phenotypes observed with TOR knockdown plants, indicating a link between TOR signaling and nutrition/light energy status. Genetic and physiological studies together with RNA sequencing and metabolite analysis of TOR-suppressed lines revealed that TOR regulates development and life span in Arabidopsis by restructuring cell growth, carbon and nitrogen metabolism, gene expression, and rRNA and protein synthesis. Gain-and loss-of-function Ribosomal Protein S6 (RPS6) mutants additionally show that TOR function involves RPS6-mediated nutrition and light-dependent growth and life span in Arabidopsis. INTRODUCTIONAmong all extant organisms, many of the longest living species are plants. For example, a creosote bush (Larrea tridentata) called King Clone, which has lived for over 10,000 years, was found in the Mojave Desert (Vasek, 1980). The giant redwood trees in California (Sequoia sempervirens) live for well over 2000 years (Scheres, 2007) and several other tree species have a long life span. However, the mechanisms that underpin longevity in plants are not known. Dissecting the control mechanisms of growth and life span in plants has many implications. It will provide a framework for addressing the key components and regulators of life span in plants. Engineering life span in plants has multiple applications, including early maturation for short seasons, long-lasting horticultural plants, and trees of desirable life span in silviculture (McCouch, 2004;Neale, 2007;Takeda and Matsuoka, 2008;Sonah et al., 2011). Recent work identified genetic factors that can be modified via breeding techniques to improve crop yield through modulating the growth phases (Moose and Mumm, 2008). Uauy et al. (2006) showed that a NAC transcription factor-mediated acceleration of senescence impacted nutrient remobilization in wheat (Triticum aestivum), resulting in significant increase in protein content and micronutrients in the grains (Uauy et al., 2006). Thus, life span alteration can have several beneficial outcomes.Plants are distinct from most other multicellular eukaryotes in having a modular body plan with immortal totipotent stem cells, sessile but autotrophic lifestyle, and very extensive biosynthetic capabilities ...

Little is known concerning the heterogeneity of mitochondrial shape, size, number, cytoplasmic distribution, and motility in planta. Ultrastructural studies using the electron microscope have shown a variety of mitochondrial shapes and sizes within fixed cells, however, it is not possible to dismiss the possibility that any heterogeneity observed resulted from preparation or fixation artefacts. Unambiguous demonstration of the extent and nature of mitochondrial heterogeneity in vivo necessitates the use of a truly in vivo mitochondrial detection system. Green fluorescent protein is an excellent in vivo marker for gene expression and protein localization studies. It is particularly useful for real-time spatiotemporal analysis of intracellular protein targeting and dynamics and as such is an ideal marker for analysing mitochondria in planta. Stably transformed Arabidopsis lines have been generated with GFP targeted to the mitochondria using either of two plant mitochondrial signal sequences from the beta-ATPase subunit or the mitochondrial chaperonin CPN-60. Mitochondrially targeted GFP, which is easily detectable using an epifluorescent or confocal microscope, highlights heterogeneity of mitochondrial shape, size, position, and dynamic within living plant cells.

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Mitochondria are vital organelles that perform a variety of fundamental functions ranging from the synthesis of ATP through to being intimately involved in programmed cell death. Comprised of at least six compartments: outer membrane, inner boundary membrane, intermembrane space, cristal membranes, intracristal space, and matrix, mitochondria have a complex, dynamic internal structure. This internal dynamism is reflected in the pleomorphy and motility of mitochondria. Mitochondria contain their own DNA (mtDNA), encoding a small number of vital genes, but this role as a genetic vault is not compatible with the role of mitochondria in bioenergetics since electron transport results in the generation of reactive oxygen species (ROS) that induce lesions in the mtDNA. It is hypothesized that ROS shape the morphological organization of the higher plant cell mitochondrial population into a discontinuous whole, and that ROS are a selective pressure affecting the organization of the mitochondrial genome. This review describes how inter- and intra-mitochondrial compartmentalization underpins the biology of this complex organelle.