Vascular Defense Responses in Rice: Peroxidase Accumulation in Xylem Parenchyma Cells and Xylem Wall Thickening

Abstract

The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae is a vascular pathogen that elicits a defensive response through interaction with metabolically active rice cells. In leaves of 12-day-old rice seedlings, the exposed pit membrane separating the xylem lumen from the associated parenchyma cells allows contact with bacterial cells. During resistant responses, the xylem secondary walls thicken within 48 h and the pit diameter decreases, effectively reducing the area of pit membrane exposed for access by bacteria. In susceptible interactions and mock-inoculated controls, the xylem walls do not thicken within 48 h. Xylem secondary wall thickening is developmental and, in untreated 65-day-old rice plants, the size of the pit also is reduced. Activity and accumulation of a secreted cationic peroxidase, PO-C1, were previously shown to increase in xylem vessel walls and lumen. Peptide-specific antibodies and immunogold-labeling were used to demonstrate that PO-C1 is produced in the xylem parenchyma and secreted to the xylem lumen and walls. The timing of the accumulation is consistent with vessel secondary wall thickening. The PO-C1 gene is distinct but shares a high level of similarity with previously cloned pathogen-induced peroxidases in rice. PO-C1 gene expression was induced as early as 12 h during resistant interactions and peaked between 18 and 24 h after inoculation. Expression during susceptible interactions was lower than that observed in resistant interactions and was undetectable after infiltration with water, after mechanical wounding, or in mature leaves. These data are consistent with a role for vessel secondary wall thickening and peroxidase PO-C1 accumulation in the defense response in rice to X. oryzae pv. oryzae.

Comparison between tracheary element lignin formation and extracellular lignin-like substance formation during the culture of isolated Zinnia elegans mesophyll cells

“…In that case, the speed and degree of lignification should be more important than its localization in the cells. In intact plants, some isoenzymes and genes of peroxidases were also shown to be expressed in response to various stresses, such as wound induction of ZmPox2 in maize (de Obeso et al 2003) and tpoxN1 in tobacco (Sasaki et al 2002), and bacterial pathogen attack induction of rice PO-C1 (Hilaire et al 2001). The idea in this study that the extracellular peroxidases would be important for the synthesis of lignin-like substance is consistent with the previous reports in intact plants.…”

Peroxidases have more functions than a Swiss army knife

“…oryzae) strongly upregulated a single peroxidase isoform in xylem parenchyma. This peroxidase was then secreted to the xylem vessels, resulting in secondary wall thickening and reducing access of the pathogen to the pit membrane (the pathogen's contact point with living cells) (Hilaire et al 2001). Lignin is not the only phenolic subunit that is used by peroxidase in defensive polymerisation reactions.…”

Specific functions of individual class III peroxidase genes

“…Infection of rice leaves by Xanthomonas oryzae pv oryzae (rice blight) induces the thickening of the secondary wall, reducing the access of the pathogen to the pit membrane, which is the pathogen's contact point in living cells (Hilaire et al, 2001). This thickening was correlated with strong induction in xylem vessels of a peroxidase, OsPrx114 (PO-C1), as shown by detection of specific antibodies.…”