Let it bloom: crosstalk between light and flowering signalling in Arabidopsis

The terrestrial environment is complex, with many parameters fluctuating on daily and seasonal basis. Plants in particular, have developed complex sensory and signalling networks to extract and integrate information about their surroundings, in order to maximise their fitness and mitigate some of the detrimental effects of their sessile lifestyles. Light and temperature each provide crucial insight on the surrounding environment and in combination allow plants to appropriately develop, grow and adapt. Crosstalk between light and temperature signalling cascades allow plants to time key developmental decisions accordingly to ensure they are “in sync” with their environment. In this review, we discuss the major players that regulate light and temperature signalling, and the cross‐talk between them, in reference to a crucial developmental decision faced by plants: to bloom or not to bloom

HISTONE DEACETYLASE 9 stimulates auxin-dependent thermomorphogenesis in Arabidopsis thaliana by mediating H2A.Z depletion

Many plant species respond to unfavorable high ambient temperatures by adjusting their vegetative body plan to facilitate cooling. This process is known as thermomorphogenesis and is induced by the phytohormone auxin. Here, we demonstrate that the chromatin-modifying enzyme HISTONE DEACETYLASE 9 (HDA9) mediates thermomorphogenesis but does not interfere with hypocotyl elongation during shade avoidance. HDA9 is stabilized in response to high temperature and mediates histone deacetylation at the YUCCA8 locus, a rate-limiting enzyme in auxin biosynthesis, at warm temperatures. We show that HDA9 permits net eviction of the H2A.Z histone variant from nucleosomes associated with YUCCA8, allowing binding and transcriptional activation by PHYTOCHROME INTERACTING FACTOR 4, followed by auxin accumulation and thermomorphogenesis

The role of TANDEM ZINC-FINGER/PLUS3 in light-regulated plant development

Abstract not currently available

The role of TZP in photoperiodic flowering

La luce è uno stimolo fondamentale per la produzione di energia, crescita della pianta, per lo sviluppo e per il continuo adattamento all’ambiente. TZP (Tandem zinc finger Plus3 domain), una proteina influenzata da luce e orologio circadiano, gioca un ruolo fondamentale nelle fasi iniziali dello sviluppo in Arabidopsis thaliana. TZP, a livello di struttura proteica, è costituita da due zinc finger domain che mediano interazioni con proteine e acidi nucleici, e da un PLUS3 domain. Il PLUS3 domain è ancora poco studiato nelle piante e agisce nel rimodellamento della cromatina e ha affinità per acidi nucleici a singolo. La funzione principale di TZP è il controllo della crescita dell’ipocotile agendo come regolatore trascrizionale per i geni coinvolti nella crescita come le perossidasi e geni coinvolti nella sintesi della parete cellulare (Loudet et al., 2008). TZP è una proteina nucleare e in particolare si localizza in strutture puntiformi, i “nuclear bodies”, siti di attiva trascrizione, dove fattori di trascrizione e fotorecettori convergono. Affinché TZP venga reclutato nei “nuclear bodies” è richiesta la presenza del fotorecettore fitocromo B (PHYB) con il quale interagisce. Recenti studi hanno dimostrato un coinvolgimento di TZP nella fioritura, in particolare, in seguito ad un’overespressione di TZP si osserva una riduzione dei tempi di fioritura della pianta (Kaiserli et al., 2015). Questo effetto sulla fioritura è stato osservato durante un fotoperiodo di 16 ore di luce e 8 ore di buio (long day). TZP influisce quindi sulla fioritura fotoperiodica, dove la regolazione della fioritura è controllata dalla lunghezza del fotoperiodo. In Arabidopsis la fioritura è promossa durante i long day e in particolare le proteine fondamentali coinvolte in questa induzione sono il fattore di trascrizione CONSTANS (CO), che è il principale induttore della proteina mobile FLOWERING LOCUS T (FT), il responsabile dell’induzione della fioritura. phyB, un importante interattore di TZP, ha un ruolo importante in questo pathway andando a mediare la degradazione di CO durante le prime ore della mattina. Lo scopo della mia tesi è lo studio del ruolo di TZP nella fioritura fotoperiodica attraverso l’utilizzo di linee transgeniche che presentano un’overespressione di TZP in dei mutanti fotoperiodici. Verrà analizzato l’impatto dell’overespressione di TZP in diversi mutanti attraverso analisi di espressione genica e attraverso esperimenti di caratterizzazione del fenotipo che vanno a misurare i tempi di fioritura. Recenti lavori suggeriscono una possibile interazione tra il pathway fotoperiodico e il pathway della vernalizzazione, in particolare attraverso il coinvolgimento di phyB. Nella seconda parte della tesi analizzerò una possibile interazione di TZP nel pathway della vernalizzazione dove TZP potrebbe agire nel controllo di FLOWERING LOCUS C (FLC) il principale repressore della fioritura

TANDEM ZINC-FINGER/PLUS3 regulates phytochrome B abundance and signaling to fine-tune hypocotyl growth

TANDEM ZINC-FINGER/PLUS3 (TZP) is a transcriptional regulator that acts at the crossroads of light and photoperiodic signaling. Here, we unveil a role for TZP in fine-tuning hypocotyl elongation under red light and long-day conditions. We provide genetic evidence for a synergistic action between TZP and PHOTOPERIODIC CONTROL OF HYPOCOTYL 1 (PCH1) in regulating the protein abundance of PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and downstream gene expression in response to red light and long days (LDs). Furthermore, we show that TZP is a positive regulator of the red/far-red light receptor and thermosensor phytochrome B (phyB) by promoting phyB protein abundance, nuclear body formation, and signaling. Our data therefore assign a function to TZP in regulating two key red light signaling components, phyB and PIF4, but also uncover a new role for PCH1 in regulating hypocotyl elongation in LDs. Our findings provide a framework for the understanding of the mechanisms associated with the TZP signal integration network and their importance for optimizing plant growth and adaptation to a changing environment

Let it bloom: cross‐talk between light and flowering signaling in Arabidopsis

The terrestrial environment is complex, with many parameters fluctuating on daily and seasonal basis. Plants in particular, have developed complex sensory and signalling networks to extract and integrate information about their surroundings, in order to maximise their fitness and mitigate some of the detrimental effects of their sessile lifestyles. Light and temperature each provide crucial insight on the surrounding environment and in combination allow plants to appropriately develop, grow and adapt. Crosstalk between light and temperature signalling cascades allow plants to time key developmental decisions accordingly to ensure they are “in sync” with their environment. In this review, we discuss the major players that regulate light and temperature signalling, and the cross‐talk between them, in reference to a crucial developmental decision faced by plants: to bloom or not to bloom

Histone Deacetylase 9 stimulates auxin-dependent thermomorphogenesis in Arabidopsis thaliana by mediating H2A.Z depletion

Many plant species respond to unfavorable high ambient temperatures by adjusting their vegetative body plan to facilitate cooling. This process is known as thermomorphogenesis and is induced by the phytohormone auxin. Here, we demonstrate that the chromatin-modifying enzyme HISTONE DEACETYLASE 9 (HDA9) mediates thermomorphogenesis but does not interfere with hypocotyl elongation during shade avoidance. HDA9 is stabilized in response to high temperature and mediates histone deacetylation at the YUCCA8 locus, a rate-limiting enzyme in auxin biosynthesis, at warm temperatures. We show that HDA9 permits net eviction of the H2A.Z histone variant from nucleosomes associated with YUCCA8, allowing binding and transcriptional activation by PHYTOCHROME INTERACTING FACTOR 4, followed by auxin accumulation and thermomorphogenesis

HISTONE DEACETYLASE 9 stimulates auxin-dependent thermomorphogenesis in Arabidopsis thaliana by mediating H2A.Z depletion

Many plant species respond to unfavorable high ambient temperatures by adjusting their vegetative body plan to facilitate cooling. This process is known as thermomorphogenesis and is induced by the phytohormone auxin. Here, we demonstrate that the chromatin-modifying enzyme HISTONE DEACETYLASE 9 (HDA9) mediates thermomorphogenesis but does not interfere with hypocotyl elongation during shade avoidance. HDA9 is stabilized in response to high temperature and mediates histone deacetylation at the YUCCA8 locus, a rate-limiting enzyme in auxin biosynthesis, at warm temperatures. We show that HDA9 permits net eviction of the H2A.Z histone variant from nucleosomes associated with YUCCA8, allowing binding and transcriptional activation by PHYTOCHROME INTERACTING FACTOR 4, followed by auxin accumulation and thermomorphogenesis