ROLE OF CHROMATIN IN WATER STRESS RESPONSES IN PLANTS

Citation:

Han, SK, Wagner D.  2013.  Role of chromatin in water stress responses in plants, Dec 3. Journal of experimental botany.

Abstract:

As sessile organisms, plants are exposed to environmental stresses throughout their life. They have developed survival strategies such as developmental and morphological adaptations, as well as physiological responses, to protect themselves from adverse environments. In addition, stress sensing triggers large-scale transcriptional reprogramming directed at minimizing the deleterious effect of water stress on plant cells. Here, we review recent findings that reveal a role of chromatin in water stress responses. In addition, we discuss data in support of the idea that chromatin remodelling and modifying enzymes may be direct targets of stress signalling pathways. Modulation of chromatin regulator activity by these signaling pathways may be critical in minimizing potential trade-offs between growth and stress responses. Alterations in the chromatin organization and/or in the activity of chromatin remodelling and modifying enzymes may furthermore contribute to stress memory. Mechanistic insight into these phenomena derived from studies in model plant systems should allow future engineering of broadly drought-tolerant crop plants that do not incur unnecessary losses in yield or growth.

Notes:

Han, Soon-KiWagner, DorisJ Exp Bot. 2013 Dec 3.

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DR DORIS WAGNER PROMOTED TO PROFESSOR OF BIOLOGY

Thank you very much, promotion committee, letter writers and department for your support. Also all present and past labmembers for your excellent contributions to our research endeavor. Last but not least, thanks to my husband John for his unwavering help and encouragment.

NSF FUNDING TO STUDY THE ROLE OF LEAFY IN FLOWER FORMATION

In annual plants, which include most crops species, onset of flower formation triggers a transition from biomass and resource production in the leaves and branches to allocation of these resources to the next generation in the seeds formed in the flowers. Both timing of the onset of flower formation and proper flower development are important for plant survival and for agriculture. Understanding the regulation of these processes will allow optimization of the duration of the vegetative phase for biofuel production or food production and optimal elaboration of the reproductive structures for food production. Despite much recent progress in the understanding of the regulation of both of these processes, much remains unknown. The plant specific transcription factor LEAFY (LFY) is a master regulator of the switch to flower formation and of early flower development. This project uses LFY as an entry point and Arabidopsis thaliana as the plant model species to address two key questions that represent major gaps in the understanding of flower development: (1) What are regulators that act downstream of LFY to trigger the switch to flower formation? LFY sets in motion the series of events that result in formation of the first flower. Despite the importance of this developmental switch for plant reproductive fitness and human sustenance, key regulators of this transition that are induced by LFY remain unidentified. We will take a novel genetic approach to address this question. (2) How do LFY and another important regulator of flower development, the MADS box transcription factor APETALA1 together direct the cell fate changes required to form a floral meristem? It is now widely accepted that LFY and AP1 together orchestrate early flower development. In this AIM insight gained from recent genomic datasets will be harnessed to identify candidate regulators important for early events in flower morphogenesis followed by elucidation of their role in plants. These early events in flower morphogenesis are poorly understood in all plant systems so this investigation should generate novel insight of broad significance.

GRAD STUDENT SOON-KI HAN RECEIVES UPENN DISSERTATION COMPLETION FELLOWSHIP

Climate change predictions suggest a loss of arable lands for crops at a time when we will likely face increased food demands due to a rise in the world population. Generation of drought tolerant crop species is therefore a high priority. Broad drought tolerance is achieved only when plants can resist multiple challenges simultaneously, such as water deficit plus high heat or light intensity, as these environmental cues show more than additive effects on plant survival. I reasoned that broad drought tolerance may depend on broad alterations in the transcriptional program of plants. It has been known for a long time that chromatin is situated at the interface between environmental cues and the accessible genome. In my Ph.D research, I therefore have explored the link between chromatin regulators known to alter genome accessibility, the SWI/SNF chromatin remodeling ATPases, and drought stress response in the plant model system Arabidopsis thaliana. My study has two general impacts. Firstly, it provides mechanistic insight how environmental stress dependent genome accessibility is regulated by the SWI/SNF chromatin remodelers. Secondly, it contributes to our understanding of the drought stress response-pathway, which is crucial for our ability to enhance plant tolerance to water stress.

POSTDOC DR NOBUTOSHI YAMAGUCHI OBTAINS A TRAVEL GRANT TO ATTEND PLANT BIOLOGY 2013

A classical role of the hormone auxin is in the formation of flowers at the periphery of the reproductive shoot apex. InArabidopsis, mutants in regulators of polar auxin transport or in the auxin responsive transcription factor MONOPTEROS (MP) form naked inflorescence ‘pins’ lacking flowers. How auxin maxima and MP direct initiation of flower primordia is poorly understood. We have identified three genes whose expression is directly induced by auxin-activated MP that furthermore jointly regulate flower primordium initiation. These three genes encode known regulators of flower development; LEAFY (LFY), which specifies floral fate and two AINTEGUMENTA and AINTEGUMENTA –LIKE6/PLETHORA3 transcription factors, key regulators of floral growth. These and additional findings that will be presented demonstrate a mechanistic link between flower primordium initiation and subsequent steps in flower morphogenesis. We further uncovered direct positive feedback from LFY to the auxin pathway. We will discuss a possible role for the newly identified ‘auxin LFY’ module in patterning organ systems in diverse plant species.

NSF FUNDING TO STUDY PLANT POLYCOMB RESPONSE ELEMENTS (PRES)

In eukaryotes, genomic DNA is highly compacted in the nucleus. This compaction renders portions of the genomic DNA inaccessible to transcription factors or the general transcriptional machinery. A large fraction of the inaccessible DNA consists of gene-poor heterochromatin. Portions of the gene-rich euchromatin are also inaccessible or silenced. A hallmark of this silencing is that it occurs only in certain conditions, for example in some cell types or in the absence of an environmental cue. In multicellular eukaryotes, euchromatic silencing is largely mediated by Polycomb repression. Polycomb repressors do not have inherent sequence specificity, they need to be targeted to the correct genomic loci. This project will identify DNA sequence motifs that direct Polycomb repressors to euchromatic genomic regions inArabidopsis thaliana for proper plant development and proper plant stress responses. The ultimate goal of the project is to be able to predict -based on the presence of the DNA sequence motifs- which genomic regions Polycomb repressors can be recruited to in this and in other plant species and to identify the sequence-specific binding factors involved in the recruitment.

A MOLECULAR FRAMEWORK FOR AUXIN-MEDIATED INITIATION OF FLOWER PRIMORDIA

Citation:

Yamaguchi, N, Wu MF, Winter CM, Berns MC, Nole-Wilson S, Yamaguchi A, Coupland G, Krizek BA, Wagner D.  2013.   A molecular framework for auxin-mediated initiation of flower primordia, Feb 11. Dev Cell. 24:271-82., Number 3

Abstract:

A classical role of the hormone auxin is in the formation of flowers at the periphery of the reproductive shoot apex. Mutants in regulators of polar auxin transport or in the auxin-responsive transcription factor MONOPTEROS (MP) form naked inflorescence “pins” lacking flowers. How auxin maxima and MP direct initiation of flower primordia is poorly understood. Here, we identify three genes whose expression is directly induced by auxin-activated MP that furthermore jointly regulate flower primordium initiation. These three genes encode known regulators of flower development: LEAFY (LFY), which specifies floral fate, and two AINTEGUMENTA-LIKE/PLETHORA transcription factors, key regulators of floral growth. Our study thus reveals a mechanistic link between flower primordium initiation and subsequent steps in flower morphogenesis. Finally, we uncover direct positive feedback from LFY to the auxin pathway. The auxin LFY module we describe may have been recruited during evolution to pattern other plant organ systems.

Notes:

Yamaguchi, NobutoshiWu, Miin-FengWinter, Cara MBerns, Markus CNole-Wilson, StaciYamaguchi, AyakoCoupland, GeorgeKrizek, Beth AWagner, DorisDev Cell. 2013 Feb 11;24(3):271-82. doi: 10.1016/j.devcel.2012.12.017. Epub 2013 Jan 31.

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