Nitric oxide (NO) is a key signaling molecule in plants. This analysis of Arabidopsis thaliana HOT5 (sensitive to hot temperatures), which is required for thermotolerance, uncovers a role of NO in thermotolerance and plant development. HOT5 encodes S-nitrosoglutathione reductase (GSNOR), which metabolizes the NO adduct S-nitrosoglutathione. Two hot5 missense alleles and two T-DNA insertion, protein null alleles were characterized. The missense alleles cannot acclimate to heat as darkgrown seedlings but grow normally and can heat-acclimate in the light. The null alleles cannot heat-acclimate as light-grown plants and have other phenotypes, including failure to grow on nutrient plates, increased reproductive shoots, and reduced fertility. The fertility defect of hot5 is due to both reduced stamen elongation and male and female fertilization defects. The hot5 null alleles show increased nitrate and nitroso species levels, and the heat sensitivity of both missense and null alleles is associated with increased NO species. Heat sensitivity is enhanced in wild-type and mutant plants by NO donors, and the heat sensitivity of hot5 mutants can be rescued by an NO scavenger. An NO-overproducing mutant is also defective in thermotolerance. Together, our results expand the importance of GSNOR-regulated NO homeostasis to abiotic stress and plant development. INTRODUCTIONNitric oxide (NO) is a short-lived, endogenously produced radical that acts as a signaling molecule in all higher organisms Wendehenne et al., 2004;Delledonne, 2005;Crawford, 2006;Besson-Bard et al., 2008). Despite its deceivingly simple structure, the rich chemistry of NO in biological systems gives rise to multiple secondary and tertiary reaction products, greatly complicating our mechanistic understanding of NO-related effects (Stamler and Hausladen, 1998;Mancardi et al., 2004;Ridnour et al., 2004). Directly and via its various chemical transformations, NO not only accomplishes signaling functions but also acts as a redox modulator with both antioxidant (by quenching other radical reactions) and pro-oxidant (through the production of reactive nitrogen species; RNS) properties. In addition to effects on redox status, the formation of RNS leads to nitrosation, nitrosylation, and nitration reactions with other molecules. Most of the regulatory effects of NO are thought to be mediated through posttranslational protein modifications, including heme nitrosylation, Tyr nitration, Cys nitrosation, and even glutathiolation (Lindermayr et al., 2005;Aracena-Parks et al., 2006;Wang et al., 2006b;West et al., 2006;Zaninotto et al., 2006).In plants, NO is believed to be produced via two different enzymatic pathways (Guo et al., 2003;Crawford, 2006). In one pathway, it is generated by nitrate reductase through the successive reduction of nitrate to nitrite and further to NO. In the other pathway, L-Arg, plus oxygen and NADPH, is converted to NO and citrulline by the action of a NO synthase, although the actual existence and identity of plant NO synthase is currently unres...

We have defined amino acids important for function of the Arabidopsis thaliana Hsp100/ClpB chaperone (AtHsp101) in acquired thermotolerance by isolating recessive, loss-of-function mutations and a novel semidominant, gain-of-function allele [hot1-4 (A499T)]. The hot1-4 allele is unusual in that it not only fails to develop thermotolerance to 458C after acclimation at 388C, but also is sensitive to 388C, which is a permissive temperature for wild-type and loss-of-function mutants. hot1-4 lies between nucleotide binding domain 1 (NBD1) and NBD2 in a coiled-coil domain that is characteristic of the Hsp100/ClpB proteins. We then isolated two classes of intragenic suppressor mutations of hot1-4: loss-of-function mutations (Class 1) that eliminated the 388C sensitivity, but did not restore thermotolerance function to hot1-4, and Class 2 suppressors that restored acquired thermotolerance function to hot1-4. Location of the hot1-4 Class 2 suppressors supports a functional link between the coiled-coil domain and both NBD1 and the axial channel of the Hsp100/ClpB hexamer. In addition, the strongest Class 2 suppressors restored solubility of aggregated small heat shock proteins (sHsps) after heat stress, revealing genetic interaction of the Hsp100/ClpB and sHsp chaperone systems. These results also demonstrate that quantitative phenotypes can be used for in vivo genetic dissection of protein mechanism in Arabidopsis.

Knee pain is second only to the back as the most commonly reported area of pain in the human body. With an overall prevalence of 46.2%, its impact on disability, lost productivity, and cost on healthcare cannot be overlooked. Due to the pervasiveness of knee pain in the general population, there are no shortages of treatment options available for addressing the symptoms. Ranging from physical therapy and pharmacologic agents to interventional pain procedures to surgical options, practitioners have a wide array of options to choose from – unfortunately, there is no consensus on which treatments are “better” and when they should be offered in comparison to others. While it is generally accepted that less invasive treatments should be offered before more invasive ones, there is a lack of agreement on the order in which the less invasive are to be presented. In an effort to standardize the treatment of this extremely prevalent pathology, the authors present an all-encompassing set of guidelines on the treatment of knee pain based on an extensive literature search and data grading for each of the available alternative that will allow practitioners the ability to compare and contrast each option.

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