Arabidopsis thaliana class III peroxidase, AT5G51890, targeted to cell wall of protoxylem cells may be involved with cell elongation and xylem formation

Secretory class III peroxidases are hypothesized to be involved with lignification and auxin catabolism. Lignification is polymerization that can strengthen the water conducting tissues and support the plant system. Auxin is growth hormone that promotes plant root growth. There are 73 peroxidases in the Arabidopsis thaliana. Determining where the protein traffics to the final location within the cell can help identify the function of each peroxidase. In this study, peroxidase AT5G51890 contains signal peptide, which directs for trafficking into endoplasmic reticulum (ER). Moreover, there is absence of hydrophobic tail in carboxyl terminal of peroxidase, which suggested that peroxidase AT5G51890 will target at cell wall. In 2009, Tokunage et al showed staining pattern of AT5G51890 promoter fused b-glucuronidase (GUS) gene expressed in vessel elements, which is one of cell types from xylem tissues coated with lignin in cell wall. Therefore, peroxidase AT5G51890 is hypothesized to be secreted out into cell wall. To determine function and cellular location of peroxidases, three genes constructs were developed by two rounds of PCR and transferred into Arabidopsis plant nuclear genomes. Endogenous SP:51890:YFP:RFVN construct contained DNA sequence of yellow fluorescent protein (YFP). Construct SP:51890:mCherry:AFVY contained mCherry DNA sequence and vacuolar sorting sequence. Construct (Delta)SP:51890:mCherry:RFVN had removal of signal peptide sequence and mCherry DNA sequence. Microscopic images showed that all peroxidase targeted variants were all found in protoxylem tissues of apical root region. Targeted variants of peroxidase 51890 designed to exploit lack of cytoplasm in dead protoxylem cells at maturity, required longer term experiments to confirm the subcellular location of peroxidase targeted variants. Initial experiment using plants containing peroxidase targeted variants to the cell wall, vacuole and cytoplasm respectively showed no significant change on cell elongation and protoxylem formation.