Thesis

An ARABIDOPSIS CLASS III Peroxidase, AT2G34060, is expressed in protoxylem of one to eight day old seedlings and involved in restriction of root length

Hydrophobic polymer lignin provides water proofing and structural integrity to cell wall which help plants adapt to terrestrial environment. Secretory peroxidases are thought to generate monolignol radicals that polymerize to form lignin. In Arabidopsis thaliana there are 73 secretory peroxidases .Identification of tissue, cellular, and subcellular location for individual peroxidases can help assigning their function. All secretory peroxidases contain signal peptide for entry into endomembrane system. Some peroxidases have hydrophobic carboxy-termini targeting to them to vacuole. Peroxidases lacking hydrophobic carboxy-terminal are targeted to wall. We tagged A. thaliana secretory peroxidase, AT2G34060, with yellow fluorescent protein. Plants transformed with this construct expressed AT2G34060 in the protoxylem cells of the roots of one to eight day old seedlings. AT2G34060 has a hydrophobic Carboxyterminal and aminotransferase domain. This peroxidase is located in vesicles arranged in a helical fluorescent pattern similar to microtubule pattern. Overexpression of AT2G34060 reduced the root length. A vesicular location and reduction in growth by overexpression suggests that AT2G43060 supports lignification by producing monolignol precursors through its putative aminotransferase ability. AT2G34060 may also be involved in deglycosylation of monolignols during their vesicular transport to the wall. The availability of monolignols may be a limiting factor in the lignification process. Therefore, a higher number of available monolignols may lead to shorter roots through higher lignification. Our work identifies a peroxidase that appears in cells undergoing lignifications and its subcellular location in vesicles is consistent with formation of lignin. Also, root shorting through overexpression is consistent with role in lignification.

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