| Summary: | Lignified plant cell walls represent an immense carbon sink to offset rising atmospheric carbon dioxide (CO₂) due to the chemical stability and structural diversity of the bonds formed between lignin subunits, making it the slowest decomposing component of dead vegetation. This thesis explores the feasibility of increasing lignin deposition in roots through overexpression of SND1 (Secondary Wall Associated NAC Domain Protein 1), a key transcriptional activator involved in regulating secondary wall biosynthesis in fibres, under the control of two different putative root-specific promoters, 4-coumarate:CoA ligase 1 (4CL1) and glutathione S-transferase-tau class 19 (GSTU19). Transgenic plants were analyzed at: 1) the molecular level (transcription of lignin pathway genes and regulatory transcription factors (TFs) involved in cell wall biosynthesis), 2) the chemical level (lignin content) and 3) the plant growth and development level (phenotyping and microscopy). Results showed that: i) SND1 was overexpressed in a tissue-specific manner in roots, ii) SND1 overexpression caused an upregulation of its previously known direct downstream targets, iii) SND1 overexpression did not result in a modification of indicative lignin biosynthetic pathway genes in roots, iv) plants overexpressing SND1 in roots generally produced plants with decreased total lignin content, v) plants overexpressing SND1 in roots generally showed an increase in lateral root density, and vi) seed traits, plant growth and development, plant height and lignin deposition patterns in roots remained unaltered. Misregulation of SND1 in roots did not result in the predicted increase in lignin deposition patterns in this organ.
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