A phloem‐localized Arabidopsis metacaspase (AtMC3) improves drought tolerance

Increasing drought phenomena pose a serious threat to agricultural productivity. Although plants have multiple ways to respond to the complexity of drought stress, the underlying mechanisms of stress sensing and signaling remain unclear. The role of the vasculature, in particular the phloem, in facilitating inter-organ communication is critical and poorly understood.Combining genetic, proteomic and physiological approaches, we investigated the role of AtMC3, a phloem-specific member of the metacaspase family, in osmotic stress responses in Arabidopsis thaliana. Analyses of the proteome in plants with altered AtMC3 levels revealed differential abundance of proteins related to osmotic stress pointing into a role of the protein in water-stress-related responses.Overexpression of AtMC3 conferred drought tolerance by enhancing the differentiation of specific vascular tissues and maintaining higher levels of vascular-mediated transportation, while plants lacking the protein showed an impaired response to drought and inability to respond effectively to the hormone abscisic acid.Overall, our data highlight the importance of AtMC3 and vascular plasticity in fine-tuning early drought responses at the whole plant level without affecting growth or yield.ISSN:0028-646XISSN:1469-813

Lichen symbiosis: nature's high yielding machines for induced hydrogen production.

Hydrogen is a promising future energy source. Although the ability of green algae to produce hydrogen has long been recognized (since 1939) and several biotechnological applications have been attempted, the greatest obstacle, being the O2-sensitivity of the hydrogenase enzyme, has not yet been overcome. In the present contribution, 75 years after the first report on algal hydrogen production, taking advantage of a natural mechanism of oxygen balance, we demonstrate high hydrogen yields by lichens. Lichens have been selected as the ideal organisms in nature for hydrogen production, since they consist of a mycobiont and a photobiont in symbiosis. It has been hypothesized that the mycobiont's and photobiont's consumption of oxygen (increase of COX and AOX proteins of mitochondrial respiratory pathways and PTOX protein of chrolorespiration) establishes the required anoxic conditions for the activation of the phycobiont's hydrogenase in a closed system. Our results clearly supported the above hypothesis, showing that lichens have the ability to activate appropriate bioenergetic pathways depending on the specific incubation conditions. Under light conditions, they successfully use the PSII-dependent and the PSII-independent pathways (decrease of D1 protein and parallel increase of PSaA protein) to transfer electrons to hydrogenase, while under dark conditions, lichens use the PFOR enzyme and the dark fermentative pathway to supply electrons to hydrogenase. These advantages of lichen symbiosis in combination with their ability to survive in extreme environments (while in a dry state) constitute them as unique and valuable hydrogen producing natural factories and pave the way for future biotechnological applications

Kinetic of hydrogen production of the lichen <i>Pleurosticta acetabulum</i> in several culture mediums.

<p>Kinetic of hydrogen production of the lichen <i>Pleurosticta acetabulum</i> in several culture mediums.</p

Proposed models for hydrogen production of the lichen <i>Pleurosticta acetabulum</i>.

<p>(A) Lichens exactly after the regeneration stage. (B) Lichens under anoxic conditions in light. (C) Lichens under anoxic conditions in dark.</p

Kinetic of hydrogen production (A) and oxygen consumption (B) of the lichen <i>Pleurosticta acetabulum</i> in several temperatures.

<p>Kinetic of hydrogen production (A) and oxygen consumption (B) of the lichen <i>Pleurosticta acetabulum</i> in several temperatures.</p

Kinetic of hydrogen production and oxygen consumption of the lichen <i>Pleurosticta acetabulum</i>.

<p>Kinetic of hydrogen production and oxygen consumption of the lichen <i>Pleurosticta acetabulum</i>.</p

Kinetic of hydrogen production of various lichen species under (A) light and (B) dark incubation.

<p>Kinetic of hydrogen production of various lichen species under (A) light and (B) dark incubation.</p

Western blot analysis images and densitometric analysis for (A) cytochromic oxidase (COX), (B) alternative oxidase (AOX), (C) plastid terminal oxidase (PTOX), (D) core protein of PSI (PsaA), (E) core protein of PSII (D1), (F) hydrogenase (HYDA) and (G) pyruvate ferredoxin oxidoreductase (PFOR) after regeneration and after 33 hours of incubation in the hermitically with septum closed bottles.

<p>C: Control (after regeneration), L: 33 hours of incubation in light, D: 33 hours of incubation in dark.</p

Kinetic of hydrogen production of the lichen <i>Pleurosticta acetabulum</i> in several initial volumes of culture medium.

<p>Kinetic of hydrogen production of the lichen <i>Pleurosticta acetabulum</i> in several initial volumes of culture medium.</p