Complexity of the heat stress response in plants.

https://eprints.cs.univie.ac.at/3231/1/0-S1874939911001787-main.pdf

The plant heat stress transcription factor (Hsf) family: structure, function and evolution.

Transcriptional Regulatory Network of Plant Heat Stress Response

Plants are sessile organisms that gauge stressful conditions to ensure survival and reproductive success. While plants in nature often encounter chronic or recurring stressful conditions, the strategies to cope with those are poorly understood. Here, we demonstrate the involvement of ARGONAUTE1 and the microRNA pathway in the adaptation to recurring heat stress (HS memory) at the physiological and molecular level. We show that miR156 isoforms are highly induced after HS and are functionally important for HS memory. miR156 promotes sustained expression of HS-responsive genes and is critical only after HS, demonstrating that the effects of modulating miR156 on HS memory do not reflect preexisting developmental alterations. miR156 targets SPL transcription factor genes that are master regulators of developmental transitions. SPL genes are posttranscriptionally downregulated by miR156 after HS, and this is critical for HS memory. Altogether, the miR156-SPL module mediates the response to recurring HS in Arabidopsis thaliana and thus may serve to integrate stress responses with development.

/pdf/arabidopsis-mir156-regulates-tolerance-to-recurring-1o8iumb85k.pdf

Arabidopsis miR156 Regulates Tolerance to Recurring Environmental Stress through SPL Transcription Factors

The diversity of plant heat stress transcription factors

The expression of heat shock proteins (Hsps) induced by nonlethal heat treatment confers acquired thermotolerance (AT) to organisms against subsequent challenges of otherwise lethal temperature. After the stress signal is removed, AT gradually decays, with decreased Hsps during recovery. AT of sufficient duration is critical for sessile organisms such as plants to survive repeated heat stress in their environment, but little is known regarding its regulation. To identify potential regulatory components, we took a reverse genetics approach by screening for Arabidopsis (Arabidopsis thaliana) T-DNA insertion mutants that show decreased thermotolerance after a long recovery (2 d) under nonstress conditions following an acclimation heat treatment. Among the tested mutants corresponding to 48 heat-induced genes, only the heat shock transcription factor HsfA2 knockout mutant showed an obvious phenotype. Following pretreatment at 37°C, the mutant line was more sensitive to severe heat stress than the wild type after long but not short recovery periods, and this could be complemented by the introduction of a wild-type copy of the HsfA2 gene. Quantitative hypocotyl elongation assay also revealed that AT decayed faster in the absence of HsfA2. Significant reduction in the transcript levels of several highly heat-inducible genes was observed in HsfA2 knockout plants after 4 h recovery or 2 h prolonged heat stress. Immunoblot analysis showed that Hsa32 and class I small Hsp were less abundant in the mutant than in the wild type after long recovery. Our results suggest that HsfA2 as a heat-inducible transactivator sustains the expression of Hsp genes and extends the duration of AT in Arabidopsis.

/pdf/a-heat-inducible-transcription-factor-hsfa2-is-required-for-ifad2ckn48.pdf

A Heat-Inducible Transcription Factor, HsfA2, Is Required for Extension of Acquired Thermotolerance in Arabidopsis

The expression of heat shock proteins (Hsps) induced by nonlethal heat treatment confers acquired thermotolerance (AT) toorganisms against subsequent challenges of otherwise lethal temperature. After the stress signal is removed, AT graduallydecays, with decreased Hsps during recovery. ATof sufﬁcient duration is critical for sessile organisms such as plants to surviverepeated heat stress in their environment, but little is known regarding its regulation. To identify potential regulatorycomponents, we took a reverse genetics approach by screening for Arabidopsis (Arabidopsis thaliana) T-DNA insertion mutantsthat show decreased thermotolerance after a long recovery (2 d) under nonstress conditions following an acclimation heattreatment. Among the tested mutants corresponding to 48 heat-induced genes, only the heat shock transcription factor HsfA2knockout mutant showed an obvious phenotype. Following pretreatment at 37 C, the mutant line was more sensitive to severeheat stress than the wild type after long but not short recovery periods, and this could be complemented by the introduction ofa wild-type copy of the HsfA2 gene. Quantitative hypocotyl elongation assay also revealed that AT decayed faster in theabsence of HsfA2. Signiﬁcant reduction in the transcript levels of several highly heat-inducible genes was observed in HsfA2knockout plants after 4 h recovery or 2 h prolonged heat stress. Immunoblot analysis showed that Hsa32 and class I small Hspwere less abundant in the mutant than in the wild type after long recovery. Our results suggest that HsfA2 as a heat-inducibletransactivator sustains the expression of Hsp genes and extends the duration of AT in Arabidopsis.

A Heat-Inducible Transcription Factor, HsfA2, Is Required for Extension of Acquired Thermotolerance

Combining acetic acid and ethanol as an anti-browning treatment for lettuce butt discoloration through repression of the activity and expression of phenylalanine ammonia lyase

Spatial–temporal analyses of lycopene and sugar contents in tomatoes during ripening using chemical shift imaging

The celery (Tall Utah, Apium graveolens var. dulce) was adopted as a model system to investigate effective methods for enhancing embryogenesis. The focus was placed on attaining the optimum gaseous composition and the mixing intensity and viscosity of culture systems. The mixing intensity was investigated by using creased flasks and evaluated by shear force index (SFI). By using different closures with different ventilation coefficients, K
 w, to adjust the gaseous composition in the flasks, it was found that embryo frequency (EF) increased with high

 $$P_{{\rm O}_2}$$
 or low ethylene concentration in the headspace of the culture flasks. Cultivating the embryogenic cells under controlled ethylene concentrations depressed EF at ethylene concentrations higher than 0.08 ppm. Moreover, 0.1 μM of CoCl2 remarkably repressed the ethylene formation in the culture medium and enhanced EF.

 $$P_{{\rm CO}_2}$$
 and

 $$P_{{\rm O}_2}$$
 around 3% and 30%, respectively, favored EF. For non-creased flasks, addition of CMC (carboxymethyl cellulose) decreased the EF and DO level of the medium, due to lowered mass transfer rate attributed to high viscosity. For creased flasks, supplementation of 0.4 g/ 100 ml CMC reduced the ill-effects of high shear stress and maximized EF (7.22%). Our results are potentially applicable to other species and large-scale embryo production systems.

Tsu-Tsuen Wang

Papers

A Heat-Inducible Transcription Factor, HsfA2, Is Required for Extension of Acquired Thermotolerance in Arabidopsis

A Heat-Inducible Transcription Factor, HsfA2, Is Required for Extension of Acquired Thermotolerance

Combining acetic acid and ethanol as an anti-browning treatment for lettuce butt discoloration through repression of the activity and expression of phenylalanine ammonia lyase

Spatial–temporal analyses of lycopene and sugar contents in tomatoes during ripening using chemical shift imaging

Induction of somatic embryos of celery by control of gaseous compositions and other physical conditions