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Role of the KNAT7 transcription factor in diurnal regulation of lignin biosynthetic genes and resource allocation in Arabidopsis thaliana

University of British Columbia

Lignified secondary cell walls in plants represent an irreversibly deposited final metabolic sink for global fixed carbon reserves and synthesis of these walls is an energetically expensive process for the plant; hence it follows that spatial-temporal control of secondary cell wall biosynthesis must be closely co-ordinated with carbon metabolism. The function of the KNOTTED ARABIDOPSIS THALIANA 7 (KNAT7) homeodomain protein, a repressor of transcription and part of the multi-level network of transcription factors regulating secondary cell wall biosynthesis and deposition, was studied to investigate its potential role in diurnal regulation of a set of lignin biosynthetic genes (LBGs) in Arabidopsis thaliana. I found that in young wild-type seedlings, transcript accumulation levels of LBGs grown in long day conditions vary diurnally but most do not show a change in temporal variation over a daily light-dark cycle in the knat7 mutant. Diurnal patterns of LBG transcript accumulation were less clear in mature wild-type inflorescence stem tissue, however diurnal expression at subjective 'dawn' was altered for some LBGs in knat7, providing evidence for a function for KNAT7 as a diurnal regulator of LBG expression in actively lignifying tissue. A diurnal regulatory function for KNAT7 is also supported by the presence of a hypocotyl elongation phenotype as well as by an altered timing to floral transition in KNAT7 mutants, phenotypes commonly displayed by mutants defective in clock regulation. Further, evidence for KNAT7 function as an activator of diurnal transcription of 3-DEOXY-D-ARABINO-HEPTULOSONATE 7-PHOSPHATE SYNTHASE 1 (DHS1) was observed in seedlings while in stems KNAT7 seemed to function as a repressor of LBGs. KNAT7 temporal expression variation itself shows minimal change in seedling and stem tissue grown in longday conditions, suggesting that post transcriptional mechanisms, such as protein-protein interactions, may be important for modulating KNAT7 functions diurnally. Overall, my data provides support for the hypothesis that diurnal regulation of transcript abundance is a function of KNAT7 in seedlings and mature stem tissue, which may represent a means to fine-tune resource (sucrose and starch) allocation to secondary cell wall biosynthesis coordinated with diurnal fluctuations in availability.

Text

2016-01-31

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/54027

Botany

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/