Papillae formation on Arabidopsis leaf trichomes requires the function of Mediator tail subunits 2, 14, 15a, 16, and 25

Fornero, Christy; Rickerd, Trevor; Kirik, Viktor

doi:10.1007/s00425-018-3063-y

Cited by 5 publications

(3 citation statements)

References 47 publications

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“…The Mediator complex is required for virtually all Pol II-mediated transcription in eukaryotes ( Jeronimo and Robert, 2017 ; Soutourina, 2018 ). As a crucial component of the Mediator complex, MED14 has long been known to play important roles in the transcription of key genes involved in various developmental processes and stress responses, including cell proliferation, shoot apical meristem development, trichome papillae development, salicylic acid-, methyl jasmonate-, and ethylene-mediated plant immune responses, abscisic acid-dependent drought responses, as well as cold and heat stress responses ( Autran et al, 2002 ; Zhang et al, 2013 ; Hemsley et al, 2014 ; Wang et al, 2016 ; Fornero et al, 2019 ; Ohama et al, 2020 ; Lee et al, 2021a ). In particular, MED14 works with MED16 and MED2 in modulating cold-responsive genes regulated by the AP2 transcription factors C-repeat binding factors, and operates with MED17 in activating heat stress-inducible genes by assisting HsfA1, a heat shock transcription factor (HSF) that functions as a master regulator of the heat stress response ( Hemsley et al, 2014 ; Ohama et al, 2020 ).…”

Section: Discussionmentioning

confidence: 99%

PHYTOCHROME-INTERACTING FACTOR 4/HEMERA-mediated thermosensory growth requires the Mediator subunit MED14

Bajracharya

Grace

et al. 2022

Plant Physiology

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While moderately elevated ambient temperatures do not trigger stress responses in plants, they do substantially stimulate the growth of specific organs through a process known as thermomorphogenesis. The basic helix-loop-helix transcription factor PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) plays a central role in regulating thermomorphogenetic hypocotyl elongation in various plant species, including Arabidopsis (Arabidopsis thaliana). Although it is well known that PIF4 and its co-activator HEMERA (HMR) promote plant thermosensory growth by activating genes involved in the biosynthesis and signaling of the phytohormone auxin, the detailed molecular mechanism of such transcriptional activation is not clear. In this report, we investigated the role of the Mediator complex in the PIF4/HMR-mediated thermoresponsive gene expression. Through the characterization of various mutants of the Mediator complex, a tail subunit named MED14 was identified as an essential factor for thermomorphogenetic hypocotyl growth. MED14 was required for the thermal induction of PIF4 target genes but had a marginal effect on the levels of PIF4 and HMR. Further transcriptomic analyses confirmed that the expression of numerous PIF4/HMR-dependent, auxin-related genes required MED14 at warm temperatures. Moreover, PIF4 and HMR physically interacted with MED14 and both were indispensable for the association of MED14 with the promoters of these thermoresponsive genes. While PIF4 did not regulate MED14 levels, HMR was required for the transcript abundance of MED14. Taken together, these results unveil an important thermomorphogenetic mechanism, in which PIF4 and HMR recruit the Mediator complex to activate auxin-related growth-promoting genes when plants sense moderate increases in ambient temperature.

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Section: Discussionmentioning

confidence: 99%

PHYTOCHROME-INTERACTING FACTOR 4/HEMERA-mediated thermosensory growth requires the Mediator subunit MED14

Bajracharya

Grace

et al. 2022

Plant Physiology

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“…The Mediator complex is required for virtually all Pol II-mediated transcription in eukaryotes (Jeronimo and Robert, 2017; Soutourina, 2018). As a crucial component of the Mediator complex, MED14 has long been known to play important roles in the transcription of key genes involved in various developmental processes and stress responses, including cell proliferation, shoot apical meristem development, trichome papillae development, salicylic acid-, methyl jasmonate-, and ethylene-mediated plant immune responses, abscisic acid-dependent drought responses, as well as cold and heat stress responses (Autran et al, 2002; Zhang et al, 2013; Hemsley et al, 2014; Wang et al, 2016; Fornero et al, 2019; Ohama et al, 2020; Lee et al, 2021a). In particular, MED14 works with MED16 and MED2 in modulating cold-responsive genes regulated by the AP2 transcription factors C-repeat binding factors (CBFs), and operates with MED17 in activating heat stress-inducible genes by assisting HsfA1, a heat shock transcription factor (HSF) that functions as a master regulator of the heat stress response (Hemsley et al, 2014; Ohama et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

PIF4/HEMERA-mediated daytime thermosensory growth requires the Mediator subunit MED14

Qiu

Bajracharya

et al. 2022

Preprint

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While moderately elevated ambient temperatures do not trigger stress responses in plants, they do significantly stimulate the growth of specific organs through a process known as thermomorphogenesis. The basic helix-loop-helix transcription factor PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) plays a central role in regulating thermomorphogenetic hypocotyl elongation in various plant species, including Arabidopsis thaliana. Although it is well known that PIF4 promotes plant thermosensory growth by activating genes involved in the biosynthesis and signaling of the phytohormone auxin, the detailed molecular mechanism of such transcriptional activation is not clear. Our previous studies demonstrated that HEMERA (HMR), a transcriptional co-activator of PIF4, promotes the thermo-induced expression of PIF4 target genes through its nine-amino-acid transactivation domain (9aaTAD). In this report, we investigate the role of the Mediator complex in the PIF4/HMR-mediated thermoresponsive gene expression. Through the characterization of various mutants of the Mediator complex, a tail subunit named MED14 is identified as an essential factor for thermomorphogenetic hypocotyl growth. MED14 is required for the thermal induction of PIF4 target genes but has a marginal effect on the levels of PIF4 and HMR. Further transcriptomic analyses confirm that the expression of numerous PIF4/HMR-dependent, auxin-related genes requires MED14 at warm temperatures. Moreover, PIF4 and HMR physically interact with MED14 and both are indispensable for the association of MED14 with the promoters of these thermoresponsive genes. Taken together, these results unveil an important thermomorphogenetic mechanism, in which PIF4 and HMR recruit the Mediator complex to activate auxin-related growth-promoting genes when plants sense moderate increases in ambient temperature.One-sentence summaryThe Mediator subunit MED14 promotes thermomorphogenesis by interacting with PHYTOCHROME-INTERACTING FACTOR 4 and HEMERA to induce the expression of growth-promoting genes at elevated temperatures.

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“…Of the two full-length genes (MED15a and MED15e), MED15a seems to be the most abundantly expressed (Pasrija and Thakur, 2012), and also has been the most focus of research. MED15a has been associated with different plant processes, including seed development (Kim et al, 2016), trichome 6 development (Fornero et al, 2019), and SA and benzothiadiazole (BTH, an SA analog) recognition (Canet et al, 2012;Medina-Puche et al, 2017). Indeed, a previous forward genetics screen for loss of BTH-induced growth inhibition also identified mutations in the MED15a KIX domain as nrb4 (non-recognition of bth 4) mutants (Canet et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

The Salicylic Acid-Mediated Growth-Immunity Tradeoff in Arabidopsis

Butselaar¹

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Plants have a dynamic immune system to protect themselves against pathogens. Recognition of a pathogen leads to the activation of this immune system, steered by different phytohormones. One of these, salicylic acid, regulates plant responses to biotrophic pathogens that thrive on living host tissue. Typical SA-mediated responses are the production of antimicrobial proteins and metabolites and the strengthening of the cell wall. These responses can occur both locally and systemically. Due to their nature, these responses cost energy and resources that cannot be invested in plant growth and development. This suppression also works the other way around: active growth and developmental processes suppress immunity. This mutual inhibition is called the growth-immunity tradeoff and is actively regulated by the plant. The research in this thesis is focused on the model plant Arabidopsis thaliana (thale cress), in which the SA content is controlled at the level of synthesis and catabolism. Two enzymes that catabolize SA through hydroxylation are the paralogous 2-oxoglutarate Fe(II)-dependent oxygenases DMR6/S5H (DOWNY MILDEW RESISTANT 6/SA 5-HYDROXYLASE) and DLO1/S3H (DMR6-LIKE OXYGENASE 1/SA 3-HYDROXYLASE). dmr6/dlo1 mutants have enhanced SA levels and therefore a constitutively active immune system and enhanced disease resistance. The high SA levels of double mutant plants cause hyperresistance but also dwarfism. On the other hand, overexpression of DMR6 or DLO1 leads to depletion of SA and thus enhanced susceptibility. We use the perturbed SA catabolism of the dmr6/dlo1 mutants and DMR6/DLO1 overexpression lines to investigate the SA-mediated growth-immunity tradeoff. We found that altered expression of DMR6 and/or DLO1 had major effects on the transcriptome that correlated to the plant’s SA content. We found that enhanced SA levels in dmr6/dlo1 mutants caused reduced photosynthetic efficiency and a sped up development and reduced SA levels in DMR6/DLO1 overexpression lines led to reduced pathogen-associated molecular pattern (PAMP)-triggered immune responses. We further identified a significant effect of the genetic background to perturbations in DMR6/DLO1 expression in different Arabidopsis accessions: several Arabidopsis accessions had a reduced growth tradeoff but retained high disease resistance. To systematically investigate the genetics behind regulation of the growth-immunity tradeoff, we further employed a forward genetics screen for restored growth and high resistance in dmr6-3 dlo1 double mutants and identified seven unique zund mutants. These plants carried mutations in known regulators of SA synthesis (ICS1, ISOCHORISMATE SYNTHASE 1), perception (NPR1, NONEXPRESSOR OF PR GENES 1), or signaling (PAD4, PHYTOALEXIN DEFICIENT 4), indicating that a suppression of SA synthesis or SA responses reduces the growth tradeoff in high immunity dmr6-3 dlo1 mutants. Three other zund mutants carried a mutation in the same gene: MED15a (MEDIATOR 15a), a component of the MEDIATOR complex for transcription initiation. We investigate the function of MED15a in the growth-immunity tradeoff in detail, and find that around 80% of dmr6-3 dlo1-induced gene expression changes are genetically dependent on the integrity of two amino acids in the MED15a kinase-inducible (KIX) domain. I discuss the implications of this research for applications to breed for sustainable disease resistance in crops.

show abstract

Papillae formation on Arabidopsis leaf trichomes requires the function of Mediator tail subunits 2, 14, 15a, 16, and 25

Cited by 5 publications

References 47 publications

PHYTOCHROME-INTERACTING FACTOR 4/HEMERA-mediated thermosensory growth requires the Mediator subunit MED14

PHYTOCHROME-INTERACTING FACTOR 4/HEMERA-mediated thermosensory growth requires the Mediator subunit MED14

PIF4/HEMERA-mediated daytime thermosensory growth requires the Mediator subunit MED14

The Salicylic Acid-Mediated Growth-Immunity Tradeoff in Arabidopsis

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