Biology subjects

Pardo, J. M.

Publications and source records attributed to Pardo, J. M..

4 recordsLinked to original sources

bioRxiv2026

Rhizoctonia theobromae isolates causing Vascular-Streak Dieback of Cocoa and Cassava Witches' Broom Disease are likely host-specific, regionally divergent and homothallic

The fastidious basidiomycete Rhizoctonia (Ceratobasidium) theobromae is a biotrophic pathogen that causes Vascular-Streak Dieback (VSD) of Theobroma cacao (cocoa). The fungus has also been identified as the cause of an emergent disease known as Cassava Witches Broom Disease (CWBD) raising concerns that the pathogen is spreading to alternative hosts and to new regions. Interestingly, while VSD of cocoa and CWBD are reported as co-present in several countries, there is currently no evidence for cross-infection between species. The fungus is difficult to culture in vitro due its slow growth and Kochs postulates have not been definitive on either host. The complete fungus life cycle therefore remains enigmatic, though studies have progressed knowledge on pathology within the both the cocoa and cassava hosts. We have conducted limited field trials and sequenced mating (MAT) and ITS loci of isolates from various infected hosts and regions. We hypothesize that (i) genetic variation at MAT loci correlates with region or host (ii) long amplicon ITS sequences between isolates are more definitive for polymorphisms (iii) life-cycle traits of R. theobromae may be inferred from MAT loci (iv) cassava grown under VSD infected cocoa will be infected and develop symptoms of CWBD. We did not find any cross-infection in field trials, and we show that the pathogen is highly homozygous, despite undergoing meiosis, indicating a predominantly homothallic life cycle. Our data indicate that the pathogen is likely host specific and regionally divergent and suggests that host specificity on cocoa and cassava evolved by selection from a common ancestor rather than a host jump.

microbiology↗

bioRxiv2025

Physical and functional interactions of the potassium uptake protein HAK5 and the nitrate transporter NPF6.2 is critical for the mineral nutrition of Arabidopsis

Potassium (K+) starvation induces the expression of gene HAK5 encoding a high-affinity K+ uptake protein, but how plants perceive the K+ status and the signaling intermediaries involved in the response remains largely unknown. To identify key regulators of K+ nutrition in Arabidopsis, a genetic screen was performed using an pHAK5:LUC reporter line, and a mutant showing stable induction of the reporter under K+-sufficient conditions was isolated. Mapping-by-sequencing identified two linked mutations affecting genes involved in K+ and nitrate nutrition, namely a loss-of-function in the K+ uptake channel AKT1 and a gain-of-function allele of the nitrate transporter NPF6.2/NRT1.4 (NPF6.2V210M) that doubled the rate of nitrate transport. We report that the physical interaction of NPF6.2 and HAK5 transport proteins resulted in reciprocal interference. Co-expression in Xenopus oocytes of NPF6.2 with the regulatory kinase CIPK23 or the mutant protein NPF6.2V210M alone inhibited HAK5 transport, whereas HAK5 inhibited nitrate transport by NPF6.2 and NPF6.2V210M. We conclude that mutation NPF6.2V210M enhanced the nutritional defects associated to the loss of AKT1 function through the inhibition of HAK5. These findings evidence an intimate molecular crosstalk between transporters involved in the mineral nutrition of plants. The mutual interference when both transport systems are operative may represent a novel integrative regulatory mechanism in mineral nutrition.

plant biology↗

bioRxiv2022

Structure-Guided Identification of Critical Residues in the Vacuolar Na+,K+/H+ Antiporter NHX1 from Arabidopsis thaliana

Cation/Proton Antiporters (CPA) acting in all biological membranes help regulate the volume and pH of cells and of intracellular organelles. A key issue with these proteins is their structure-function relationships since they present intrinsic regulatory features that rely on structural determinants, including pH-sensitivity and the stoichiometry of ion exchange. Crystal structures are only available for prokaryotic CPA, whereas the eukaryotic ones have been modeled using the former as templates. Here we show an updated and improved structural model of the tonoplast-localized K+,Na+/H+ antiporter NHX1 of Arabidopsis as a representative of the vacuolar NHX family that is key to the accumulation of K+ into plant vacuoles. Conserved residues judged as functionally important were mutated and the resulting protein variants were tested for activity in the yeast Saccharomyces cerevisiae. Results indicate that residue N184 in the ND-motif characteristic of CPA1 could be replaced by the DD-motif of CPA2 family members with minimal consequences on activity, yet this residue may help to regulate the optimal pH range of the exchanger. Attempts to alter the electroneutrality of AtNHX1 by different combinations of amino acid replacements at N184, R353 and R390 residues resulted in inactive or partly active proteins with differential ability to control the vacuolar pH of the yeast.

plant biology↗

bioRxiv2021

A Calcium/Palmitoylation Switch Interfaces the Signaling Networks of Stress Response and Transition to Flowering

The precise timing of flowering in adverse environments is critical for plants to secure reproductive success. We report a novel mechanism controlling the time of flowering by which the palmitoylation-dependent nuclear import of protein SOS3/CBL4, a Ca2+-signaling intermediary in the plant response to salinity, results in the selective stabilization of the flowering time regulator GIGANTEA inside the nucleus under salt stress, while degradation of GIGANTEA in the cytosol releases the protein kinase SOS2 to achieve salt tolerance. S-acylation of SOS3 was critical for its nuclear localization and the promotion of flowering, but dispensable for salt tolerance. SOS3 interacted with the photoperiodic flowering components GIGANTEA and FKF1 on the CONSTANS gene promoter to sustain the transcription of CO and FT under salinity. Thus, SOS3 acts as a Ca2+- and palmitoylation-dependent molecular switch that fine-tunes flowering in a saline environment through the shared spatial separation and selective stabilization of GIGANTEA. The SOS3 protein connects two signaling networks to co-regulate stress adaptation and time of flowering. Short summaryS-acylation promoted the nuclear import of SOS3/CBL4 for the selective stabilization of the photoperiodic floral regulator GIGANTEA to fine-tune flowering time in a saline environment. Spatial separation of SOS3 acts as a molecular switch co-regulating stress adaptation and time of flowering.

plant biology↗