Changes in the allocation of endogenous strigolactone improve plant biomass production on phosphate-poor soils.

Strigolactones (SLs) are carotenoid-derived phytohormones shaping plant architecture and inducing the symbiosis with endomycorrhizal fungi. In Petunia hybrida, SL transport within the plant and towards the rhizosphere is driven by the ABCG-class protein PDR1. PDR1 expression is regulated by phytohormones and by the soil phosphate abundance, and thus SL transport integrates plant development with nutrient conditions. We overexpressed PDR1 (PDR1 OE) to investigate whether increased endogenous SL transport is sufficient to improve plant nutrition and productivity. Phosphorus quantification and nondestructive X-ray computed tomography were applied. Morphological and gene expression changes were quantified at cellular and whole tissue levels via time-lapse microscopy and quantitative PCR. PDR1 OE significantly enhanced phosphate uptake and plant biomass production on phosphate-poor soils. PDR1 OE plants showed increased lateral root formation, extended root hair elongation, faster mycorrhization and reduced leaf senescence. PDR1 overexpression allowed considerable SL biosynthesis by releasing SL biosynthetic genes from an SL-dependent negative feedback. The increased endogenous SL transport/biosynthesis in PDR1 OE plants is a powerful tool to improve plant growth on phosphate-poor soils. We propose PDR1 as an as yet unexplored trait to be investigated for crop production. The overexpression of PDR1 is a valuable strategy to investigate SL functions and transport routes.

An antiviral trap made of protein nanofibrils and iron oxyhydroxide nanoparticles.

Minimizing the spread of viruses in the environment is the first defence line when fighting outbreaks and pandemics, but the current COVID-19 pandemic demonstrates how difficult this is on a global scale, particularly in a sustainable and environmentally friendly way. Here we introduce and develop a sustainable and biodegradable antiviral filtration membrane composed of amyloid nanofibrils made from food-grade milk proteins and iron oxyhydroxide nanoparticles synthesized in situ from iron salts by simple pH tuning. Thus, all the membrane components are made of environmentally friendly, non-toxic and widely available materials. The membrane has outstanding efficacy against a broad range of viruses, which include enveloped, non-enveloped, airborne and waterborne viruses, such as SARS-CoV-2, H1N1 (the influenza A virus strain responsible for the swine flu pandemic in 2009) and enterovirus 71 (a non-enveloped virus resistant to harsh conditions, such as highly acidic pH), which highlights a possible role in fighting the current and future viral outbreaks and pandemics.

Strigolactones Play an Important Role in Shaping Exodermal Morphology via a KAI2-Dependent Pathway.

The majority of land plants have two suberized root barriers: the endodermis and the hypodermis (exodermis). Both barriers bear non-suberized passage cells that are thought to regulate water and nutrient exchange between the root and the soil. We learned a lot about endodermal passage cells, whereas our knowledge on hypodermal passage cells (HPCs) is still very scarce. Here we report on factors regulating the HPC number in Petunia roots. Strigolactones exhibit a positive effect, whereas supply of abscisic acid (ABA), ethylene, and auxin result in a strong reduction of the HPC number. Unexpectedly the strigolactone signaling mutant d14/dad2 showed significantly higher HPC numbers than the wild-type. In contrast, its mutant counterpart max2 of the heterodimeric receptor DAD2/MAX2 displayed a significant decrease in HPC number. A mutation in the Petunia karrikin sensor KAI2 exhibits drastically decreased HPC amounts, supporting the hypothesis that the dimeric KAI2/MAX2 receptor is central in determining the HPC number.

Simulated microgravity and the antagonistic influence of strigolactone on plant nutrient uptake in low nutrient conditions.

Human-assisted space exploration will require efficient methods of food production. Large-scale farming in presence of an Earth-like atmosphere in space faces two main challenges: plant yield in microgravity and plant nutrition in extraterrestrial soils, which are likely low in nutrients compared to terrestrial farm lands. We propose a plant-fungal symbiosis (i.e. mycorrhiza) as an efficient tool to increase plant biomass production in extraterrestrial environments. We tested the mycorrhization of Solanaceae on the model plant Petunia hybrida using the arbuscular mycorrhizal fungus Rhizophagus irregularis under simulated microgravity (s0-g) conditions obtained through a 3-D random positioning machine. Our results show that s0-g negatively affects mycorrhization and plant phosphate uptake by inhibiting hyphal elongation and secondary branching. However, in low nutrient conditions, the mycorrhiza can still support plant biomass production in s0-g when colonized plants have increased SL root exudation. Alternatively, s0-g in high nutrient conditions boosts tissue-specific cell division and cell expansion and overall plant size in Petunia, which has been reported for other plants species. Finally, we show that the SL mimic molecule rac-GR24 can still induce hyphal branching in vitro under simulated microgravity. Based on these results, we propose that in nutrient limited conditions strigolactone root exudation can challenge the negative microgravity effects on mycorrhization and therefore might play an important role in increasing the efficiency of future space farming.

Asymmetric localizations of the ABC transporter PaPDR1 trace paths of directional strigolactone transport.

Strigolactones, first discovered as germination stimulants for parasitic weeds [1], are carotenoid-derived phytohormones that play major roles in inhibiting lateral bud outgrowth and promoting plant-mycorrhizal symbiosis [2-4]. Furthermore, strigolactones are involved in the regulation of lateral and adventitious root development, root cell division [5, 6], secondary growth [7], and leaf senescence [8]. Recently, we discovered the strigolactone transporter Petunia axillaris PLEIOTROPIC DRUG RESISTANCE 1 (PaPDR1), which is required for efficient mycorrhizal colonization and inhibition of lateral bud outgrowth [9]. However, how strigolactones are transported through the plant remained unknown. Here we show that PaPDR1 exhibits a cell-type-specific asymmetric localization in different root tissues. In root tips, PaPDR1 is co-expressed with the strigolactone biosynthetic gene DAD1 (CCD8), and it is localized at the apical membrane of root hypodermal cells, presumably mediating the shootward transport of strigolactone. Above the root tip, in the hypodermal passage cells that form gates for the entry of mycorrhizal fungi, PaPDR1 is present in the outer-lateral membrane, compatible with its postulated function as strigolactone exporter from root to soil. Transport studies are in line with our localization studies since (1) a papdr1 mutant displays impaired transport of strigolactones out of the root tip to the shoot as well as into the rhizosphere and (2) DAD1 expression and PIN1/PIN2 levels change in plants deregulated for PDR1 expression, suggestive of variations in endogenous strigolactone contents. In conclusion, our results indicate that the polar localizations of PaPDR1 mediate directional shootward strigolactone transport as well as localized exudation into the soil.