TPK gene products mediate cAMP-independent thermotolerance in Saccharomyces cerevisiae

Abstract

Incubation of Succharomyces cereuisiae with the plant cytokinin W-(A2-isopentenyl)adenine (2iP) resulted in an induction of thermotolerance similar to that induced by sublethal temperatures. Intracellular cAMP levels did not change significantly either during incubation at a sublethal temperature or in the presence of 2iP or ethanol. This suggested that stress-induced thermotolerance is triggered by a mechanism independent of cAMP activation. However, measurement of stress-induced thermotolerance in two mutant strains (tpkl, tpk2, TPK3; tpkl, TPK2, tpk3) each deficient in two of the catalytic subunits of the CAMP-dependent protein kinase (cAPK), revealed that sublethal heat induces thermotolerance by a mechanism part-mediated by the catalytic subunits of cAPK. In contrast, 2iP and ethanol induced thermotolerance by a mechanism fully dependent on the catalytic subunits of cAPK for expression. Therefore, this implies there must be an alternative novel mechanism, other than CAMP, for activating cAPK during stress. Sublethal heating resulted in large increases in intracellular trehalose levels which correlated with the induction of thermotolerance. However, incubation in 2iP or ethanol had no significant effect. This suggests trehalose synthesis is either coincidental with heat stress or that different stress factors induce thermotolerance by alternative mechanisms. Incubation with protein synthesis inhibitors reduced the levels of trehalose synthesized during sublethal heating, suggesting that synthesis of trehalose-6-phosphate synthase during heat stress could be accounting for the increased trehalose levels.

Neutral trehalase Nth1p of Saccharomyces cerevisiae encoded by the NTH1 gene is a multiple stress responsive protein

“…Some workers have shown increased trehalose accumulation in the presence of CuSO 4 and CHX under special conditions, for example, after a longer incubation time or with different concentrations of the chemicals or different growth conditions [34, 40]. Similar to our data, Coote et al [42] showed that CHX did not lead to increase in trehalose level in growing cells. In another study [43], it was shown that a non‐lethal concentration of the chemical stressor called tetrachloroisophthalonitrile (TPN) led to induction of expression of stress proteins; however, trehalose level did not increase.…”

Nutritional upshift response of ribosomal protein gene transcription in Saccharomyces cerevisiae

“…In a first analysis of the signal transduction pathway that IS involved in the glucose-induced transcriptional activation of yeast rp-genes, we obtained evidence that cAMP does not act as the principal second messenger in this pathway [4] In these experiments we made use of the Icrl mu- Pka actwlty and with pkcl deletion strata DL376 (B) The growth medmm of DL376 was supplemented with 1 M sorbltol [6] tant [11], in which, due to a defect in the adenylate cyclase gene, the level of mtracellutar cAMP does not increase upon addition of glucose We extended these studies by investigating the nutritional response in a mutant lacking the regulatory subunIt Bcylp of protem kmase A (Pka) and hawng low constitutwe protein kinase A actwity due to deletions of the two catalytic subunit genes TPK2 and TPK3 and a TPK1 w mutation In the third [8] Consistent with recent findings of Struhl and Klein (12), no upshIft occurred in this mutant (Fig 2A) Apparently, control of Pka actwity, probably through Bcylp, Is a major determmant m the upshtft response, although not dependmg on the intracellular cAMP concentration Similar observations have been made for other processes, which are induced by glucose but nevertheless are also cAMP-independent, like activation of trehalase [13] or control of glycolytlc flux [14] In addition, actwatlon of Pka, independent of changes in cAMP levels, has been reported to occur after exposing yeast to heat shock [15] To our knowledge, our data are the first evidence that regulation of transcription, too, may be mediated through protein klnase A but in a cAMP-Independent fashion…”

Disruption of Maize Kernel Growth and Development by Heat Stress (Role of Cytokinin/Abscisic Acid Balance)

“…5; Table I). The role of cytokinins in the acquisition of increased thermotolerance has been documented in a few plant systems such as tobacco leaves (Itai et al, 1978), maize seedlings (Caers et al, 1985), and potato tubers (Mauk and Langille, 1978), and in Saccharomyces cerevisiae (Coote et al, 1992). However, the data presented here provide evidence that levels of heat stress that disrupt maize kernel development also decrease endogenous cytokinin levels and that stem infusion of cytokinins during heat stress provides increased thermotolerance to developing maize kernels.…”