The transcription factor HSFA7b controls thermomemory at the shoot apical meristem by regulating ethylene biosynthesis and signaling in Arabidopsis

The shoot apical meristem(SAM)is responsible for overall shoot growth by generating all aboveground structures.Recent research has revealed that the SAM displays an autonomous heat stress(HS)memory of a previous non-lethal HS event.Considering the importance of the SAM for plant growth,it is essential to determine how its thermomemory is mechanistically controlled.Here,we report that HEAT SHOCK TRAN-SCRIPTION FACTOR A7b(HSFA7b)plays a crucial role in this process in Arabidopsis,as the absence of functional HSFA7b results in the temporal suppression of SAM activity after thermopriming.We found that HSFA7b directly regulates ethylene response at the SAM by binding to the promoter of the key ethylene signaling gene ETHYLENE-INSENSITIVE 3 to establish thermotolerance.Moreover,we demonstrated that HSFA7b regulates the expression of ETHYLENE OVERPRODUCER 1(ETO1)and ETO1-LIKE 1,both of which encode ethylene biosynthesis repressors,thereby ensuring ethylene homeostasis at the SAM.Taken together,these results reveal a crucial and tissue-specic role for HSFA7b in thermomemory at the Arabidopsis SAM.

Systems Biology of Plant-Microbiome Interactions

In natural environments,plants are exposed to diverse microbiota that they interact with in complex ways.While plant-pathogen interactions have been intensely studied to understand defense mechanisms in plants,many microbes and microbial communities can have substantial beneficial effects on their plant host.Such beneficial effects include improved acquisition of nutrients,accelerated growth,resilience against pathogens,and improved resistance against abiotic stress conditions such as heat,drought,and salinity.However,the beneficial effects of bacterial strains or consortia on their host are often cultivar and species specific,posing an obstacle to their general application.Remarkably,many of the signals that trigger plant immune responses are molecularly highly similar and often identical in pathogenic and beneficial microbes.Thus,it is unclear what determines the outcome of a particular microbe-host interaction and which factors enable plants to distinguish beneficials from pathogens.To unravel the complex network of genetic,microbial,and metabolic interactions,including the signaling events mediating microbe-host interactions,comprehensive quantitative systems biology approaches will be needed.

Calcium Signaling during Reproduction and Biotrophic Fungal Interactions in Plants

Many recent studies have indicated that cellular communications during plant reproduction, fungal invasion, and defense involve identical or similar molecular players and mechanisms. Indeed, pollen tube invasion and sperm release shares many common features with infection of plant tissue by fungi and oomycetes, as a tip-growing intruder needs to communicate with the receptive cells to gain access into a cell and tissue. Depending on the comPatibility between cells, interactions may result in defense, inva- sion, growth support, or cell death. Plant cells stimulated by both pollen tubes and fungal hyphae secrete, for example, small cysteine-rich proteins and receptor-like kinases are activated leading to intracellular signaling events such as the production of reactive oxygen species （ROS） and the generation of calcium （Ca^2＋） transients. The ubiquitous and versatile second messenger Ca^2＋ thereafter plays a central and crucial role in modulating numerous downstream signaling processes. In stimulated cells, it elicits both fast and slow cellular responses depending on the shape, frequency, amplitude, and duration of the Ca^2＋ transients. The various Ca^2＋ signatures are transduced into cellular information via a battery of Ca^2＋-binding proteins. In this review, we focus on Ca^2＋ signaling and discuss its occurrence during plant reproduction and interactions of plant cells with biotrophic filamentous microbes. The participation of Ca^2＋ in ROS signaling pathways is also discussed.

Old dog,new trick:The PHR-SPX system regulates arbuscular mycorrhizal symbiosis

Plant growth depends on the continuous availability of the macro-nutrient phosphate(Pi).However,in most soils,Pi is only poorly accessible to plants,resulting in Pi deficiency and triggering a number of Pi starvation responses.One strategy of plants to over-come Pi limitation is to form a symbiosis with arbuscular mycor-rhizal(AM)fungi(Smith et al.,2011),which occurs with approximately 80%of land plants.AM fungi improve the uptake of Pi and other mineral nutrients and thereby increase plant performance and stress tolerance.They collect these minerals with an extraradical hyphal network from the soil and release them from highly branched structures,called arbuscules,into root cortex cells.Interestingly,Pi sufficiency causes inhibition of internal root colonization(Balzergue et al.,2011;Breuillin et al.,2010).The mechanistic basis for this has long remained obscure.Two studies have now solved this long-standing mystery and demonstrated that a canonical Pi-response regulatory module regulates AM symbiosis in accordance with the plant Pi status(Shi et al.,2021;Das et al.,2022).