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 ...

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Anaerobic treatment dramatically alters the patterns of gene expression in maize (Zea mays L.) seedlings. During anaerobiosis there is an immediate repression of pre-existing protein synthesis, with the concurrent initiation of a selective synthesis of approx. 20 proteins. Among these anaerobic proteins are enzymes involved in glycolysis and related processes. However, inducible genes that have different functions were also found; these may function in other, perhaps more long-term, processes of adaptations to flooding, such as aerenchyma formation and root-tip death. In this article we review our recent work on maize responses to flooding stress, which has addressed two questions: how are these gene expression changes initiated and how do they lead to adaptation to flooding stress? Our results indicate that an early rise in cytosolic Ca(2+), as well as a quick establishment of ionic homeostasis, may be essential for the induction of adaptive changes at the cellular as well as organismal level.

Based on pharmacological evidence, we previously proposed that intracellular Ca2+ mediates the perception of O2 deprivation in maize seedlings. Herein, using fluorescence imaging and photometry of Ca2+ in maize suspension-cultured cells, the proposal was further investigated. Two complementary approaches were taken: (1) real time analysis of anoxia-induced changes in cytosolic Ca2+ concentration ([Ca]i) and (2) experimental manipulation of [Ca]i and then assay of the resultant anoxia-specific responses. O2 depletion caused an immediate increase in [Ca2+]i, and this was reversible within a few seconds of reoxygenation. The [Ca]i elevation proceeded independent of extracellular Ca2+. The kinetics of the Ca2+ response showed that it occurred much earlier than any detectable changes in gene expression. Ruthenium red blocked the anoxic [Ca]i elevation and also the induction of adh1 (encoding alcohol dehydrogenase) and sh1 (encoding sucrose synthase) mRNA. Ca2+, when added along with ruthenium red, prevented the effects of the antagonist on the anoxic responses. Verapamil and bepridil failed to block the [Ca]i rise induced by anoxia and were equally ineffective on anoxic gene expression. Caffeine induced an elevation of [Ca]i as well as ADH activity under normoxia. The data provide direct evidence for [Ca]i elevation in maize cells as a result of anoxia-induced mobilization of Ca2+ from intracellular stores. Furthermore, any manipulation that modified the [Ca]i rise brought about a parallel change in the expression of two anoxia-inducible genes. Thus, these results corroborate our proposal that [Ca]i is a physiological transducer of anoxia signals in plants.

Rapid Alkalinization Factors (RALFs) are plant peptides that rapidly increase the pH of plant suspension cell culture medium and inhibit root growth. A pollen-specific tomato (Solanum lycopersicum) RALF (SlPRALF) has been identified. The SlPRALF gene encodes a preproprotein that appears to be processed and released from the pollen tube as an active peptide. A synthetic SlPRALF peptide based on the putative active peptide did not affect pollen hydration or viability but inhibited the elongation of normal pollen tubes in an in vitro growth system. Inhibitory effects of SlPRALF were detectable at concentrations as low as 10 nm, and complete inhibition was observed at 1 μ  m peptide. At least 10-fold higher levels of alkSlPRALF, which lacks disulfide bonds, were required to see similar effects. A greater effect of peptide was observed in low-pH-buffered medium. Inhibition of pollen tube elongation was reversible if peptide was removed within 15 min of exposure. Addition of 100 nm SlPRALF to actively growing pollen tubes inhibited further elongation until tubes were 40 to 60 μm in length, after which pollen tubes became resistant to the peptide. The onset of resistance correlated with the timing of the exit of the male germ unit from the pollen grain into the tube. Thus, exogenous SlPRALF acts as a negative regulator of pollen tube elongation within a specific developmental window.

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