SUMMARYLong-distance communication between leaves and roots are key to properly regulate the uptake of trace metals from the soil. The molecular basis of this shoot-to-root signaling is currently unknown. In this manuscript, we describe the role of OPT3 in the shoot-to-root signaling of the iron status in Arabidopsis. We also show that reduced expression of OPT3 induces an over-accumulation of the toxic metal cadmium, but not other metals, in seeds.

Auxin (IAA) is an important regulator of plant development and root differentiation. Although recent studies indicate that salicylic acid (SA) may also be important in this context by interfering with IAA signaling, comparatively little is known about its impact on the plant's physiology, metabolism, and growth characteristics. Using carbon-11, a short-lived radioisotope (t 1/2 = 20.4 min) administered as 11 CO 2 to maize plants (B73), we measured changes in these functions using SA and IAA treatments. IAA application decreased total root biomass, though it increased lateral root growth at the expense of primary root elongation. IAA-mediated inhibition of root growth was correlated with decreased 11 CO 2 fixation, photosystem II (PSII) efficiency, and total leaf carbon export of 11 C-photoassimilates and their allocation belowground. Furthermore, IAA application increased leaf starch content. On the other hand, SA application increased total root biomass, 11 CO 2 fixation, PSII efficiency, and leaf carbon export of 11 C-photoassimilates, but it decreased leaf starch content. IAA and SA induction patterns were also examined after root-herbivore attack by Diabrotica virgifera to place possible hormone crosstalk into a realistic environmental context. We found that 4 days after infestation, IAA was induced in the midzone and root tip, whereas SA was induced only in the upper proximal zone of damaged roots. We conclude that antagonistic crosstalk exists between IAA and SA which can affect the development of maize plants, particularly through alteration of the root system's architecture, and we propose that the integration of both signals may shape the plant's response to environmental stress.

Opening of the mitochondrial permeability transition (MPT) pore leads to necrotic cell death. Excluding cyclophilin D (CypD), the makeup of the MPT pore remains conjecture. The purpose of these experiments was to identify novel MPT modulators by analyzing proteins that associate with CypD. We identified Fas-activated serine/threonine phosphoprotein kinase domain-containing protein 1 (FASTKD1) as a novel CypD interactor. Overexpression of FASTKD1 protected mouse embryonic fibroblasts (MEFs) against oxidative stress-induced reactive oxygen species (ROS) production and cell death, whereas depletion of FASTKD1 sensitized them. However, manipulation of FASTKD1 levels had no effect on MPT responsiveness, Ca2+-induced cell death, or antioxidant capacity. Moreover, elevated FASTKD1 levels still protected against oxidative stress in CypD-deficient MEFs. FASTKD1 overexpression decreased Complex-I-dependent respiration and ΔΨm in MEFs, effects that were abrogated in CypD-null cells. Additionally, overexpression of FASTKD1 in MEFs induced mitochondrial fragmentation independent of CypD, activation of Drp1, and inhibition of autophagy/mitophagy, whereas knockdown of FASTKD1 had the opposite effect. Manipulation of FASTKD1 expression also modified oxidative stress-induced caspase-3 cleavage yet did not alter apoptotic death. Finally, the effects of FASTKD1 overexpression on oxidative stress-induced cell death and mitochondrial morphology were recapitulated in cultured cardiac myocytes. Together, these data indicate that FASTKD1 supports mitochondrial homeostasis and plays a critical protective role against oxidant-induced death.

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Opening of the mitochondrial permeability transition (MPT) pore is known to mediate cellular necrosis in response to a number of toxic stimuli, such as elevated Ca 2+ levels and oxidative stress, and therefore contributes to multiple pathologies 1 . However, the identity of the components that make up the channel-forming unit of the MPT pore remain uncertain, with many candidates being ruled out by genetic studies 2,3 , and only cyclophilin-D (CypD) confirmed as a key regulator of the MPT pore 2,3 . A previous study identified the mitochondrial AAA-protease subunit spastic paraplegia 7 (SPG7) as a novel modulator of the MPT pore 4 . They reported that SPG7 interacted with CypD and that depletion of SPG7 in HEK-293 cells greatly attenuated Ca 2+ and oxidative stress-induced MPT and cell death. The authors concluded that SPG7 was an essential component of the MPT pore. They additionally reported that depletion of NipS-nap2 (also known as Gbas), a mitochondrial protein of unknown function, also attenuated MPT. The latter was interesting, Halestrap's group have also identified NipS-nap2 as a CypD-binding protein 5 .However, there are issues with the authors' conclusions. As pointed out by others 6 , MPT still occurs in the SPG7 deficient cells albeit at higher Ca 2+ concentrations. Consequently, the authors' data would indicate that SPG7 is instead a positive regulator of the MPT pore, akin to CypD, rather than the essential channel-forming unit. Moreover, indirect effects cannot be ruled out and it has been suggested that SPG7's ability to regulate MPT is through proteolysis of the Ca 2+ -import machinery, rather than a direct effect 7,8 . The discrepancies are further complicated by the report that depletion of SPG7 has no effect or even exacerbates MPT 7 . Thus, there is considerable controversy regarding a role for SPG7 in the regulation MPT. Moreover, there have been no studies aimed at reproducing the NipSnap2 experiments.To address this, we depleted (siRNA) and overexpressed (adenovirus) SPG7 or NipSnap2 in primary culture mouse-embryonic fibroblasts (MEFs) isolated from male and female C57BL/6J e15.5 embryos. MEF isolation was approved by the University of Missouri Animal Care and Usage Committee and was in accordance with the Guidelines for the Care and Use of Laboratory Animals published by the National Institutes of Health. We then assessed Ca 2+ -induced MPT and oxidative stress-induced death. First, as a positive control, we knocked down CypD (Fig. 1a) and measured MPT using the Ca 2+ -retention capacity (CRC) assay, confirming an attenuated MPT response in the CypD-depleted MEFs (Fig. 1b). Oxidative stress-induced necrosis is mediated in part by opening of the MPT pore and we demonstrated that CypD knockdown could markedly attenuate the degree of cell death to increasing concentrations of H 2 O 2 (Fig. 1c).In contrast to CypD, knockdown of SPG7 or NipSnap2 (Fig. 1d) had no observable effect on the MPT response to Ca 2+ in MEFs (Fig. 1e). Consistent with this finding, depletion of either protein did not ...

Background The mitochondrial mRNA‐binding protein FASTKD1 (Fas‐activated serine/threonine [FAST] kinase domain–containing protein 1) protects myocytes from oxidative stress in vitro. However, the role of FASTKD1 in the myocardium in vivo is unknown. Therefore, we developed cardiac‐specific FASTKD1 transgenic mice to test the effects of this protein on experimental myocardial infarction (MI). Methods and Results Transgenic mouse lines with cardiac myocyte‐specific overexpression of FASTKD1 to varying degrees were generated. These mice displayed normal cardiac morphological features and function at the gross and microscopic levels. Isolated cardiac mitochondria from all transgenic mouse lines showed normal mitochondrial function, ATP levels, and permeability transition pore activity. Male nontransgenic and transgenic mice from the highest‐expressing line were subjected to 8 weeks of permanent coronary ligation. Of nontransgenic mice, 40% underwent left ventricular free wall rupture within 7 days of MI compared with 0% of FASTKD1‐overexpressing mice. At 3 days after MI, FASTKD1 overexpression did not alter infarct size. However, increased FASTKD1 resulted in decreased neutrophil and increased macrophage infiltration, elevated levels of the extracellular matrix component periostin, and enhanced antioxidant capacity compared with control mice. In contrast, markers of mitochondrial fusion/fission and apoptosis remained unaltered. Instead, transcriptomic analyses indicated activation of the integrated stress response in the FASTKD1 transgenic hearts. Conclusions Cardiac‐specific overexpression of FASTKD1 results in viable mice displaying normal cardiac morphological features and function. However, these mice are resistant to MI‐induced cardiac rupture and display altered inflammatory, extracellular matrix, and antioxidant responses following MI. Moreover, these protective effects were associated with enhanced activation of the integrated stress response.