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Indole-3-acetic acid is a physiological inhibitor of TORC1 in yeast.

ABSTRACT: Indole-3-acetic acid (IAA) is the most common, naturally occurring phytohormone that regulates cell division, differentiation, and senescence in plants. The capacity to synthesize IAA is also widespread among plant-associated bacterial and fungal species, which may use IAA as an effector molecule to define their relationships with plants or to coordinate their physiological behavior through cell-cell communication. Fungi, including many species that do not entertain a plant-associated life style, are also able to synthesize IAA, but the physiological role of IAA in these fungi has largely remained enigmatic. Interestingly, in this context, growth of the budding yeast Saccharomyces cerevisiae is sensitive to extracellular IAA. Here, we use a combination of various genetic approaches including chemical-genetic profiling, SAturated Transposon Analysis in Yeast (SATAY), and genetic epistasis analyses to identify the mode-of-action by which IAA inhibits growth in yeast. Surprisingly, these analyses pinpointed the target of rapamycin complex 1 (TORC1), a central regulator of eukaryotic cell growth, as the major growth-limiting target of IAA. Our biochemical analyses further demonstrate that IAA inhibits TORC1 both in vivo and in vitro. Intriguingly, we also show that yeast cells are able to synthesize IAA and specifically accumulate IAA upon entry into stationary phase. Our data therefore suggest that IAA contributes to proper entry of yeast cells into a quiescent state by acting as a metabolic inhibitor of TORC1.

SUBMITTER: Nicastro R

PROVIDER: S-EPMC7978357 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background: The overproduction of the main auxin indole-3-acetic acid (IAA) in Sinorhizobium meliloti RD64 leads to beneficial effects both in free-living rhizobium and in host plant during symbiosis. These effects could be related to alteration in gene expression induced by IAA. Preliminary studies of these alterations induced in free-living cells have already started. In this work the transcriptional profiles of free-living S. meliloti wild type 1021 and RD64 strains obtained by RNA-seq analysis were used to better investigate this issue. Results: Transcriptome analysis by next-generation sequencing (RNA-seq) allowed the identification of the genes differentially expressed in RD64 cells, grown in a rich medium under aerobic conditions. Most of the up-regulated genes can be classified into two main categories. The first class comprised the main regulator fixJ and the two intermediate regulators fixK and nifA, which control the expression of genes involved in nitrogen-fixation. For these two latter genes the highest expression levels were observed. Several other genes, known to be FixJ targets, such as those involved in denitrification process and proline metabolism, were also identified. The second class of up-regulated genes comprised the gene coding for the sigma factor RpoH1 and other genes regulated in RpoH1-dependent manner in S. meliloti and involved in stress response. The main category of genes negatively affected can be classified in transport of sugars and other small molecules, chemotaxis and cell envelope functions. Under microaerobic condition, quantitative real-time PCR analysis of genes coding for the two-component regulatory system FixJL and for the regulator NifA showed that for all three genes the induction levels measured in RD64 cells were even higher when compared to aerobic conditions. In particular, for the fixJ gene the expression level increased more than tenfold. The up-regulation of nifA gene was also observed under aerobic conditions both when nitrogen level in the medium was limiting and when it was high. Conclusion: This work provided evidence that the overexpression of the auxin IAA in S. meliloti free-living cells triggers the induction of many genes involved in bacterial response to different abiotic stresses and allows the expression of key genes involved in nitrogen fixation.

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Indole-3-acetic acid is a physiological inhibitor of TORC1 in yeast.

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