Niche separation in cross-feeding sustains bacterial strain diversity across nutrient environments and may increase chances for survival in nutrient-limited leaf apoplasts

The leaf microbiome plays a crucial role in plant's health and resilience to stress. Like in other hosts, successful colonization is dependent on multiple factors, among them, resource accessibility. The apoplast is an important site of plant-microbe interactions where nutrients are tightly regulated. While leaf pathogens have evolved elaborate strategies to obtain nutrients there, it is not yet clear how commensals survive without most of these adaptations. Resource limitation can promote metabolic interactions, which in turn shape and stabilize microbiomes but this has not been addressed in detail in leaves. Here, we investigated whether and how the nutrient environment might influence metabolic exchange and assembly of bacterial communities in Flaveria trinervia and F. robusta leaves. We enriched bacteria from both plant species in-vitro in minimal media with sucrose as a carbon source, and with or without amino acids. After enrichment, we studied the genetic and metabolic diversity within the communities. Enriched Pseudomonas koreensis strains could cross-feed from diverse leaf bacteria. Although P. koreensis could not utilize sucrose, cross-feeding diverse metabolites from Pantoea sp ensured their survival in the sucrose-only enrichments. The Pseudomonas strains had high genetic similarity (~99.8% ANI) but still displayed clear niche partitioning, enabling them to simultaneously cross-feed from Pantoea. Interestingly, cross-feeders were only enriched from F. robusta and not from F. trinervia. Untargeted metabolomics analysis of the leaf apoplasts revealed contrasting nutrient environments, with greater concentrations of high-cost amino acids in F. trinervia. Additionally, P. koreensis strains were better able to survive without a cross-feeding partner in these richer apoplasts. Thus, cross feeding might arise as an adaptation to cope with nutrient limitations in the apoplast. Understanding how apoplast resources influence metabolic interactions could therefore provide plant breeders targets to manipulate leaf microbiome shape and stability.

FITORREMEDIACIÓN in situ EN MÉXICO: UNA REVISIÓN

En México, la contaminación por elementos potencialmente tóxicos en el suelo y el agua representa importantes problemas ecológicos y de salud. Las plantas capaces de crecer en terrenos antropogénicamente modificados reflejan su capacidad de adaptación a diversas condiciones ambientales. La mayoría de los estudios de fitorremediación se lleva a cabo en condiciones de laboratorio, y sólo unos pocos estudios evalúan la capacidad de fitoextracción in situ. Esta revisión resume la información obtenida de fuentes científicas sobre los estudios de fitorremediación in situ realizados en México. El 85% de los estudios reportados corresponde a sitios contaminados con metales traza por actividades mineras. Se describen plantas con potencial para ser utilizadas como acumuladoras o hyperacumuladoras de elementos potencialmente tóxicos, como Hydrocotyle ranunculoides, Parietaria pensylvanica y Commelina diffusa para Zn; Rorippa nasturtium-aquaticum y Simsia amplexicaulis para Cu; Nicotina glauca, Flaveria angustifolia y Flaveria trinervia para As y Buddleja scordioides para la fitoremediación de suelos contaminados por Pb. Las especies de plantas nativas deben estudiarse para establecer mecanismos de fitoextracción de metales y la interacción agua-suelo-microorganismos para mejorar la eficiencia de la fitorremediación in situ. La información aquí descrita tiene utilidad para planificar la remediación de sitios contaminados por elementos potencialmente tóxicos en México y para diferentes sitios del mundo.

Targeted misexpression of NAC052, acting in H3K4 demethylation, alters leaf morphological and anatomical traits in Arabidopsis thaliana

In an effort to identify genetic regulators for the cell ontogeny around the veins in Arabidopsis thaliana leaves, an activation-tagged mutant line with altered leaf morphology and altered bundle sheath anatomy was characterized. This mutant had a small rosette area with wrinkled leaves and chlorotic leaf edges, as well as enhanced chloroplast numbers in the (pre-)bundle sheath tissue. It had a bundle-specific promoter from the gene GLYCINE DECARBOXYLASE SUBUNIT-T from the C4 species Flaveria trinervia (GLDTFt promoter) inserted in the coding region of the transcriptional repressor NAC052, functioning in H3K4 demethylation, in front of an alternative start codon in-frame with the natural start codon. Reconstruction of the mutation event of our activation-tagged line by creating a line expressing an N-terminally truncated sequence of NAC052 under control of the GLDTFt promoter confirmed the involvement of NAC052 in leaf development. Our study not only reveals leaf anatomic and transcriptomic effects of an N-terminally truncated NAC052 under control of the GLDTFt promoter, but also identifies NAC052 as a novel genetic regulator of leaf development.