Ectomycorrhizal symbiosis prepares its host locally and systemically for abiotic cue signaling

Tree growth and survival are dependent on their ability to perceive signals, integrate them, and trigger timely and fitted molecular and growth responses. While ectomycorrhizal symbiosis is a predominant tree-microbe interaction in forest ecosystems, little is known about how and to what extent it helps trees cope with environmental changes. We hypothesized that the presence of Laccaria bicolor influences abiotic cue perception by Populus trichocarpa and the ensuing signaling cascade. We submitted ectomycorrhizal or non-ectomycorrhizal P. trichocarpa cuttings to short-term cessation of watering or ozone fumigation to focus on signaling networks before the onset of any physiological damage. Poplar gene expression, metabolite levels, and hormone levels were measured in several organs (roots, leaves, mycorrhizas) and integrated into networks. We discriminated the signal responses modified or maintained by ectomycorrhization. Ectomycorrhizas buffered hormonal changes in response to short-term environmental variations systemically prepared the root system for further fungal colonization and alleviated part of the root abscisic acid (ABA) signaling. The presence of ectomycorrhizas in the roots also modified the leaf multi-omics landscape and ozone responses, most likely through rewiring of the molecular drivers of photosynthesis and the calcium signaling pathway. In conclusion, P. trichocarpa-L. bicolor symbiosis results in a systemic remodeling of the host's signaling networks in response to abiotic changes. In addition, ectomycorrhizal, hormonal, metabolic, and transcriptomic blueprints are maintained in response to abiotic cues, suggesting that ectomycorrhizas are less responsive than non-mycorrhizal roots to abiotic challenges.

Long-Term High-Temperature Stress Impacts on Embryo and Seed Development in Brassica napus

Brassica napus (rapeseed) is the second most important oilseed crop worldwide. Global rise in average ambient temperature and extreme weather severely impact rapeseed seed yield. However, fewer research explained the phenotype changes caused by moderate-to-high temperatures in rapeseed. To investigate these events, we determined the long-term response of three spring cultivars to different temperature regimes (21/18°C, 28/18°C, and 34/18°C) mimicking natural temperature variations. The analysis focused on the plant appearance, seed yield, quality and viability, and embryo development. Our microscopic observations suggest that embryonic development is accelerated and defective in high temperatures. Reduced viable seed yield at warm ambient temperature is due to a reduced fertilization rate, increased abortion rate, defective embryonic development, and pre-harvest sprouting. Reduced auxin levels in young seeds and low ABA and auxin levels in mature seeds may cause embryo pattern defects and reduced seed dormancy, respectively. Glucosinolates and oil composition measurements suggest reduced seed quality. These identified cues help understand seed thermomorphogenesis and pave the way to developing thermoresilient rapeseed.

Transcriptional, hormonal, and metabolic changes in susceptible grape berries under powdery mildew infection

Grapevine (Vitis vinifera) berries are extremely sensitive to infection by the biotrophic pathogen Erysiphe necator, causing powdery mildew disease with deleterious effects on grape and wine quality. The combined analysis of the transcriptome and metabolome associated with this common fungal infection has not been previously carried out in any fruit. In order to identify the molecular, hormonal, and metabolic mechanisms associated with infection, healthy and naturally infected V. vinifera cv. Carignan berries were collected at two developmental stages: late green (EL33) and early véraison (EL35). RNA sequencing combined with GC-electron impact ionization time-of-flight MS, GC-electron impact ionization/quadrupole MS, and LC-tandem MS analyses revealed that powdery mildew-susceptible grape berries were able to activate defensive mechanisms with the involvement of salicylic acid and jasmonates and to accumulate defense-associated metabolites (e.g. phenylpropanoids, fatty acids). The defensive strategies also indicated organ-specific responses, namely the activation of fatty acid biosynthesis. However, defense responses were not enough to restrict fungal growth. The fungal metabolic program during infection involves secretion of effectors related to effector-triggered susceptibility, carbohydrate-active enzymes and activation of sugar, fatty acid, and nitrogen uptake, and could be under epigenetic regulation. This study also identified potential metabolic biomarkers such as gallic, eicosanoic, and docosanoic acids and resveratrol, which can be used to monitor early stages of infection.

Mutations in tomato 1-aminocyclopropane carboxylic acid synthase2 uncover its role in development beside fruit ripening

The role of ethylene in plant development is mostly inferred from its exogenous application. The usage of mutants affecting ethylene biosynthesis proffers a better alternative to decipher its role. In tomato (Solanum lycopersicum), 1-aminocyclopropane carboxylic acid synthase2 (ACS2) is a key enzyme regulating ripening-specific ethylene biosynthesis. We characterised two contrasting acs2 mutants; acs2-1 overproduces ethylene, has higher ACS activity, and has increased protein levels, while acs2-2 is an ethylene underproducer, displays lower ACS activity, and has lower protein levels than wild type. Consistent with high/low ethylene emission, the mutants show opposite phenotypes, physiological responses, and metabolomic profiles compared with the wild type. The acs2-1 mutant shows early seed germination, faster leaf senescence, and accelerated fruit ripening. Conversely, acs2-2 has delayed seed germination, slower leaf senescence, and prolonged fruit ripening. The phytohormone profiles of mutants were mostly opposite in the leaves and fruits. The faster/slower senescence of acs2-1/acs2-2 leaves correlated with the endogenous ethylene/zeatin ratio. The genetic analysis showed that the metabolite profiles of respective mutants co-segregated with the homozygous mutant progeny. Our results uncover that besides ripening, ACS2 participates in the vegetative and reproductive development of tomato. The distinct influence of ethylene on phytohormone profiles indicates the intertwining of ethylene action with other phytohormones in regulating plant development.

Mutations in tomato 1-aminocyclopropane carboxylic acid synthase2 uncover its role in development beside fruit ripening

The role of ethylene in plant development is mostly inferred from its exogenous application. The usage of mutants affecting ethylene biosynthesis proffers a better alternative to decipher its role. In tomato (Solanum lycopersicum), 1-aminocyclopropane carboxylic acid synthase2 (ACS2) is a key enzyme regulating ripening-specific ethylene biosynthesis. We characterised two contrasting acs2 mutants; acs2-1 overproduces ethylene, has higher ACS activity, and has increased protein levels, while acs2-2 is an ethylene underproducer, displays lower ACS activity, and has lower protein levels than wild type. Consistent with high/low ethylene emission, the mutants show opposite phenotypes, physiological responses, and metabolomic profiles compared with the wild type. The acs2-1 mutant shows early seed germination, faster leaf senescence, and accelerated fruit ripening. Conversely, acs2-2 has delayed seed germination, slower leaf senescence, and prolonged fruit ripening. The phytohormone profiles of mutants were mostly opposite in the leaves and fruits. The faster/slower senescence of acs2-1/acs2-2 leaves correlated with the endogenous ethylene/zeatin ratio. The genetic analysis showed that the metabolite profiles of respective mutants co-segregated with the homozygous mutant progeny. Our results uncover that besides ripening, ACS2 participates in the vegetative and reproductive development of tomato. The distinct influence of ethylene on phytohormone profiles indicates the intertwining of ethylene action with other phytohormones in regulating plant development.