Mitochondrial RTG (an acronym for ReTroGrade) signaling plays a cytoprotective role under various intracellular or environmental stresses. We have previously shown its contribution to osmoadaptation and capacity to sustain mitochondrial respiration in yeast. Here, we studied the interplay between RTG2, the main positive regulator of the RTG pathway, and HAP4, encoding the catalytic subunit of the Hap2-5 complex required for the expression of many mitochondrial proteins that function in the tricarboxylic acid (TCA) cycle and electron transport, upon osmotic stress. Cell growth features, mitochondrial respiratory competence, retrograde signaling activation, and TCA cycle gene expression were comparatively evaluated in wild type and mutant cells in the presence and in the absence of salt stress. We showed that the inactivation of HAP4 improved the kinetics of osmoadaptation by eliciting both the activation of retrograde signaling and the upregulation of three TCA cycle genes: citrate synthase 1 (CIT1), aconitase 1 (ACO1), and isocitrate dehydrogenase 1 (IDH1). Interestingly, their increased expression was mostly dependent on RTG2. Impaired respiratory competence in the HAP4 mutant does not affect its faster adaptive response to stress. These findings indicate that the involvement of the RTG pathway in osmostress is fostered in a cellular context of constitutively reduced respiratory capacity. Moreover, it is evident that the RTG pathway mediates peroxisomes–mitochondria communication by modulating the metabolic function of mitochondria in osmoadaptation.

Biosensors are low‐cost and low‐maintenance alternatives to conventional analytical techniques for biomedical, industrial and environmental applications. Biosensors based on whole microorganisms can be genetically engineered to attain high sensitivity and specificity for the detection of selected analytes. While bacteria‐based biosensors have been extensively reported, there is a recent interest in yeast‐based biosensors, combining the microbial with the eukaryotic advantages, including possession of specific receptors, stability and high robustness. Here, we describe recently reported yeast‐based biosensors highlighting their biological and technical features together with their status of development, that is, laboratory or prototype. Notably, most yeast‐based biosensors are still in the early developmental stage, with only a few prototypes tested for real applications. Open challenges, including systematic use of advanced molecular and biotechnological tools, bioprospecting, and implementation of yeast‐based biosensors in electrochemical setup, are discussed to find possible solutions for overcoming bottlenecks and promote real‐world application of yeast‐based biosensors.

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