Biology subjects

Ricardi, M.

Publications and source records attributed to Ricardi, M..

4 recordsLinked to original sources

bioRxiv2025

Functional auxin signaling and phosphorus acquisition triggered in planta by the extremophile bacterium Pseudomonas extremaustralis

Pseudomonas extremaustralis 14-3b, a strain isolated from Antarctica, was evaluated for plant-growth-promoting traits under different oxygen conditions. Genomic analysis revealed genes related to phosphorus solubilization and indole-3-acetic acid (IAA) biosynthesis. In vitro assays confirmed its ability to solubilize tricalcium phosphate and produce gluconic acid. IAA production was higher under microaerobic conditions compared to aerobic cultures. Using Arabidopsis thaliana DII-VENUS reporter lines, we confirmed in vivo IAA perception in roots, with reduced VENUS fluorescence upon bacterial inoculation, regardless of prior oxygen conditions. Confocal microscopy showed root surface colonization and internal localization in cotyledons, including sub-stomatal spaces. Morphological changes in A. thaliana included reduced primary root length and increased root hair length. In wheat, P. extremaustralis exhibited chemotaxis toward root exudates and colonized root tissues. After 30 days in pot experiments, inoculated wheat plants showed significantly higher stem dry weight and leaf phosphorus content than control plants. These findings indicate that P. extremaustralis promotes plant growth through multiple mechanisms, supporting its potential as a bioinoculant under variable environmental conditions, including low oxygen availability.

microbiology↗

bioRxiv2023

Fever like temperature impacts on Staphylococcus aureus and Pseudomonas aeruginosa interaction, physiology, and virulence both in vitro and in vivo

BackgroundStaphylococcus aureus and Pseudomonas aeruginosa cause a wide variety of bacterial infections and coinfections, showing a complex interaction that involves the production of different metabolites and metabolic changes. Temperature is a key factor for bacterial survival and virulence and within the host, bacteria could be exposed to an increment in temperature during fever development. We analyzed the previously unexplored effect of fever-like temperatures (39{degrees}C) on S. aureus USA300 and P. aeruginosa PAO1 microaerobic mono- and co-cultures compared with 37{degrees}C, by using RNAseq and physiological assays including in-vivo experiments. ResultsIn general terms both temperature and co-culturing had a strong impact on both PA and SA with the exception of the temperature response of monocultured PA. We studied metabolic and virulence changes on both species. Altered metabolic features at 39{degrees}C included arginine biosynthesis and the periplasmic glucose oxidation in S. aureus and P. aeruginosa monocultures respectively. When PA co-cultures were exposed at 39{degrees}C they upregulated ethanol oxidation related genes along with an increment in organic acid accumulation. Regarding virulence factors, monocultured SA showed an increase in the mRNA expression of the agr operon and hld, pms and pms{beta} genes at 39{degrees}C. Supported by mRNA data, we performed physiological experiments and detected and increment in hemolysis, staphylxantin production and a decrease in biofilm formation at 39{degrees}C. On the side of PA monocultures, we observed increase in extracellular lipase and protease and biofilm formation at 39{degrees}C along with a decrease in motility in correlation with changes observed at mRNA abundance. Additionally, we assessed host-pathogen interaction both in-vitro and in-vivo. S. aureus monocultured at 39{degrees}C showed a decrease in cellular invasion and an increase in IL-8 -but not in IL-6- production by A549 cell line. PA also decreased its cellular invasion when monocultured at 39{degrees}C and did not induce any change in IL-8 or IL-6 production. PA strongly increased cellular invasion when co-cultured at 37{degrees}C and 39{degrees}C. Finally, we observed increased lethality in mice intranasally inoculated with S. aureus monocultures pre-incubated at 39{degrees}C and even higher levels when inoculated with co-cultures. The bacterial burden for P. aeruginosa was higher in liver when the mice were infected with co-cultures previously incubated at 39{degrees}C comparing with 37{degrees}C. ConclusionOur results highlight a relevant change in the virulence of bacterial opportunistic pathogens exposed to fever-like temperatures in presence of competitors, opening new questions related to bacteria-bacteria and host-pathogen interactions and coevolution.

microbiology↗

bioRxiv2022

Arabidopsis pollen Prolyl-hydroxylases P4H4/6 are required for correct hydroxylation and secretion of LRX11 in pollen tubes

Major constituents of the plant cell walls are structural proteins that belong to the Hydroxyproline-rich glycoprotein family. Leucine-rich repeat extensis are contain a leucine-rich domain and a C-terminal domain with repetitive Ser-Pro(3-5) motifs plausible to be glycosylated. We have demonstrated that pollen-specific LRX8-11 from Arabidopsis thaliana are necessary to maintain the integrity of the pollen tube cell wall during polarized growth. In classical EXTs and likely in LRXs, proline residues are converted to hydroxyproline by Prolyl-4-hydroxylases, thus defining novel O-glycosylation sites. In this context, we aimed to determine whether hydroxylation and subsequent O-glycosylation of Arabidopsis pollen LRXs are necessary for their proper function and cell wall localization in pollen tubes. We hypothesized that pollen-expressed P4H4 and P4H6 catalyze the hydroxylation of the proline units present in Ser-Pro(3-5) motifs of LRX8-LRX11. Here, we show the p4h4-1 p4h6-1 double mutant exhibits a significant reduction in pollen germination rates and a slight reduction in pollen tube length. Pollen germination is also inhibited by specific P4Hs inhibitors, suggesting that prolyl hydroxylation is required for pollen tube development. Plants expressing pLRX11::LRX11-GFP in the p4h4-1 p4h6-1 background show partial relocalization of LRX11-GFP from the pollen tube tip apoplast to the cytoplasm. Finally, IP-MS- MS analysis revealed a decrease in oxidized prolines in LRX11-GFP in the p4h4-1 p4h6-1 background when compared to lrx11 plants expressing pLRX11::LRX11-GFP. Together, these results suggest that P4H4 and P4H6 are required for pollen germination and are also involved in LRX11 hydroxylation necessary for its localization at the cell wall of pollen tubes. One Sentence SummaryPollen-expressed P4H4 and P4H6 are required for pollen germination and for proper hydroxylation and secretion of LRX11 in pollen tubes.

plant biology↗

bioRxiv2019

A cell surface O-glycosylated peptide, AGP21, acts on the brassinosteroid pathway and modulates root hair cell fate

Root hairs (RHs) develop from specialized epidermal cells called trichoblasts, whereas epidermal cells that lack RHs are known as atrichoblasts. The mechanism controlling root epidermal cell fate is only partially understood. Root epidermis cell fate is regulated by a transcription factor complex that promotes the expression of the homeodomain protein GLABRA 2 (GL2), which blocks RH development by inhibiting ROOT HAIR DEFECTIVE 6 (RHD6). Suppression of GL2 expression activates RHD6, a series of downstream TFs including ROOT HAIR DEFECTIVE 6 LIKE-4 (RSL4 [Yi et al. 2010]) and their target genes, and causes epidermal cells to develop into RHs. Brassinosteroids (BRs) influence root epidermis cell fate. In the absence of BRs, phosphorylated BIN2 (a Type-II GSK3-like kinase) inhibits a protein complex that directly downregulates GL2 [Chen et al. 2014]. Here, we show that the genetic and pharmacological perturbation of the arabinogalactan peptide (AG) AGP21 in Arabidopsis thaliana, triggers aberrant RH development, similar to that observed in plants with defective BR signaling. We reveal that an O-glycosylated AGP21 peptide, which is positively regulated by BZR1, a transcription factor activated by BR signaling, affects RH cell fate by altering GL2 expression in a BIN2-dependent manner. These results suggest that perturbation of a cell surface AGP disrupts BR responses and inhibits the downstream effect of BIN2 on the RH repressor GL2 in root epidermal cells. In addition, AGP21 also acts in a BR-independent, AGP-dependent mode that together with BIN2 signalling cascade controls RH cell fate. SignificanceIn the plant Arabidopsis thaliana, the root epidermis forms in an alternating pattern atrichoblasts with trichoblast cells that end up developing root hairs (RHs). Atrichoblast cell fate is directly promoted by the transcription factor GLABRA2 (GL2) while the lack of GL2 allows RH formation. The loss of AGP21 peptide triggers an abnormal RH cell fate in two contiguous cells in a similar manner as brassinosteroid (BRs) mutants. In the absence of BR signaling, BIN2 (a GSK3 like-kinase) in a phosphorylated state, downregulate GL2 expression to trigger RH cell fate. The absence of AGP21 is able to repress GL2 expression and activates the expression of RSL4 and EXP7 root hair proteins.

plant biology↗