ExDNA is found in various organisms, including plants. However, plant exDNA has thus far received little attention related to its origin and role in the RET (root extracellular trap). In this study, we performed the first high-throughput genomic sequencing of plant exDNA from a Fabaceae with worldwide interest: soybean (Glycine max (L.) Merr.). The origin of this exDNA was first investigated in control condition, and the results show high-coverage on organelles (mitochondria/plastid) DNA relative to nuclear DNA, as well as a mix of coding and non-coding sequences. In the second part of this study, we investigated if exDNA release was modified during an elicitation with PEP-13 (a peptide elicitor from oomycete genus Phytophthora). Our results show that treatment of roots with PEP-13 does not affect the composition of exDNA.

The root extracellular trap (RET) has emerged as a specialized compartment consisting of root AC-DC and mucilage. However, the RET’s contribution to plant defense is still poorly understood. While the roles of polysaccharides and glycoproteins secreted by root AC-DC have started to be elucidated, how the low-molecular-weight exudates of the RET contribute to root defense is poorly known. In order to better understand the RET and its defense response, the transcriptomes, proteomes and metabolomes of roots, root AC-DC and mucilage of soybean (Glycine max (L.) Merr, var. Castetis) upon elicitation with the peptide PEP-13 were investigated. This peptide is derived from the pathogenic oomycete Phytophthora sojae. In this study, the root and the RET responses to elicitation were dissected and sequenced using transcriptional, proteomic and metabolomic approaches. The major finding is increased synthesis and secretion of specialized metabolites upon induced defense activation following PEP-13 peptide elicitation. This study provides novel findings related to the pivotal role of the root extracellular trap in root defense.

Nowadays, many products are available in the plant biostimulants market. Among them, living yeast-based biostimulants are also commercialized. Given the living aspect of these last products, the reproducibility of their effects should be investigated to ensure end-users’ confidence. Therefore, this study aimed to compare the effects of a living yeast-based biostimulant between two different soybean cultures. These two cultures named C1 and C2 were conducted on the same variety and soil but in different locations and dates until the VC developmental stage (unifoliate leaves unrolled), with Bradyrhizobium japonicum (control and Bs condition) and with and without biostimulant coating seed treatment. The foliar transcriptomic analysis done first showed a high gene expression difference between the two cultures. Despite this first result, a secondary analysis seemed to show that this biostimulant led to a similar pathway enhancement in plants and with common genes even if the expressed genes were different between the two cultures. The pathways which seem to be reproducibly impacted by this living yeast-based biostimulant are abiotic stress tolerance and cell wall/carbohydrate synthesis. Impacting these pathways may protect the plant from abiotic stresses and maintain a higher level of sugars in plant.

In perennial plants, abiotic and biotic stresses may occur in combination and/or in sequence over many years, making understanding and predicting the combined effects of drought and pathogens on plant health and productivity a considerable challenge. In this study, we investigated the susceptibility of esca-symptomatic grapevines (Vitis vinifera L.) to drought. Esca is a grapevine vascular disease leading to decreased vineyard longevity worldwide. Using transplanted, naturally infected 20-yr-old “Sauvignon blanc” vines with known esca histories, we subjected esca-symptomatic and asymptomatic control vines to different drought periods. Whole-plant and leaf physiology, radial growth, anatomical traits, and long-term recovery were compared among treatments. Esca leaf symptoms were associated with stem xylem vessel occlusion, leaf drop, and decreased symptomatic leaf gas exchange, resulting in reduced canopy area and thus, lower whole canopy transpiration. When esca-symptomatic plants were subjected to drought, declines in water potential, CO2 assimilation and stomatal conductance measured on green leaves, as well as canopy maximum transpiration, were delayed. Water stress did not cause a significant increase in stem xylem occlusion. The esca-symptomatic stems showed greater radial stem diameter recovery that coincided with faster regrowth of healthy new shoots at the top of the plant associated with a recovery of whole plant gas exchange. Esca mitigates the effects of drought through reduced canopy area, confirming an antagonistic interaction between these stresses. These results demonstrate the importance of combining abiotic and biotic stresses and understanding their interactions when studying dieback in the climate change context.

Biotic and abiotic stresses alter the physiology of perennial plants, with consequences for fungal endophytes and disease expression. In grapevine, drought inhibits esca disease expression, but the underlying molecular interactions between the plant and fungi are unknown. We combined wood metatranscriptomics, metabolomics, and metabarcoding to investigate these interactions in 30‐year‐old grapevines and eight wood‐pathogenic fungi under conditions of drought or esca leaf symptom expression. Both esca and drought decreased grapevine transpiration, but with different underlying mechanisms that induced specific transcriptomic and metabolic signatures. Similar pathways were also activated, including the phenylpropanoid and stilbenoid synthesis pathways. These stress responses could potentially confer cross‐tolerance and elicit different fungal molecular responses. Across all fungi, the total level of putative virulence factors increased significantly under both stresses. Under drought, only the relative abundance of Phaeomoniella chlamydospora and gene expression involved in anti‐oxidative mechanisms, growth, and reproduction increased. Under esca expression conditions, only the relative abundance of Fomitiporia mediterranea and gene expression involved in wood degradation, competition, detoxification, and growth increased. Under drought, induced grapevine defenses and reduced transpiration, together with the low abundance and putatively weak virulence of F. mediterranea may account for the inhibition of esca leaf symptom.