Studer, A. | bioRxiv Science

bioRxiv2025

Loss of plasma membrane conductance in outside-xylem zone explains non-stomatal control of transpiration

The conventional assumption is that stomatal conductance (gs) dominates the regulation of water and carbon dioxide fluxes between leaves and the atmosphere. Here, a nanoreporter of water status at the mesophyll cell surface and local xylem within intact maize leaves documents significant undersaturation of water vapor in the outside-xylem zone (OXZ) and a large loss of conductance of this zone (goxz) at moderate xylem water stress (no turgor loss). The ratio of the resistances (1/goxz)/(1/gs) serves as a predictive phenotype of undersaturation, non-stomatal regulation of transpiration, errors in standard gas exchange analysis, and an increase of intrinsic water use efficiency (iWUE). Cell-scale access to water status reveals symplasmic-apoplasmic disequilibrium and informs a biophysical model that can explain experimental observations quantitatively based on localization of variable conductance to the plasma membrane. This work opens new paths of inquiry into the molecular basis and functional consequences of non-stomatal regulation of transpiration.

plant biology↗

bioRxiv2024

Identification of genes involved in Kranz anatomy evolution of non-model grasses using unsupervised machine learning

Kranz syndrome is a set of leaf anatomical and functional characteristics of species using C4 photosynthesis. The current model for the evolution of C4 photosynthesis from a C3 ancestor proposes a series of gradual anatomical changes followed by a biochemical adaptation of the C4 cycle enzymatic machinery. In this work, leaf anatomical traits from closely related C3, C4 and intermediate species (Proto-Kranz, PK) were analyzed together with gene expression data to discover potential drivers for the establishment of Kranz anatomy using unsupervised machine learning. Species-specific Self-Organizing Maps (SOM) were developed to group features (genes and phenotypic traits) into clusters (neurons) according to their expression along the leaf developmental gradient. The analysis with SOM allowed us to identify candidate genes as enablers of key anatomical traits differentiation related to the area of mesophyll (M) and bundle sheath (BS) cells, vein density, and the interface between M and BS cells. At the same time, we identified a small subset of genes that displaced together with the change in the area of the BS cell along evolution suggesting a salient role in the origin of Kranz anatomy in grasses. HighlightKranz syndrome is a set of leaf anatomical and functional characteristics of species using C4 photosynthesis. We discovered, with a novel machine learning methodology, some key genes for Kranz differentiation.

plant biology↗