Increase in BrAO1 gene expression and aldehyde oxidase activity during clubroot development in Chinese cabbage (Brassica rapa L.)

Abstract

SUMMARY In clubroot disease, gall formation is induced by infection with the obligate biotroph Plasmodiophora brassicae due to increased levels of auxins and cytokinins. Because aldehyde oxidase (AO) may be involved in auxin biosynthesis in plants, we isolated two AO genes (BrAO1 and BrAO2) from Chinese cabbage (Brassica rapa ssp. pekinensis cv. Muso), which are the most similar to AAO1 among Arabidopsis AO genes, and examined their expressions during clubroot development. The expression of BrAO1 was enhanced in inoculated roots from 15 days post-inoculation (dpi) when visible clubroots were still undetectable. Thereafter, BrAO1 expression increased with clubroot development compared with uninoculated roots, although BrAO2 expression was repressed. In situ hybridization revealed that BrAO1 was strongly expressed in tissues that were invaded by immature plasmodia at 35 dpi, suggesting that BrAO1 expression was enhanced by the pathogen in order to establish its pathogenesis. In addition, we detected AO activity, as evidenced by the occurrence of at least six bands (BrAO-a to BrAO-f) in the roots of Chinese cabbage using an active staining method with benzaldehyde and indlole-3-aldehyde as the substrate. Coincidental with BrAO1 expression, the signals of BrAO-a and BrAO-d increased with inoculation by P. brassicae during clubroot development compared with healthy roots, resulting in an increase in total AO activity. By contrast, the band BrAO-b decreased post-inoculation, in parallel with the expression of BrAO2. The other bands of activity were not clearly influenced by the infection. Based on these results, we discuss the involvement of AO in auxin-overproduction during clubroot development in Chinese cabbage.

What can we learn from clubroots: alterations in host roots and hormone homeostasis caused by Plasmodiophora brassicae

“…The Arabidopsis nit1 mutant was more tolerant to clubroot, and antisense plants for the NIT2 gene revealed retarded gall development Neuhaus et al 2000). In B. rapa, a different pathway for IAA synthesis via the intermediate indole-3-acetaldehyde (IAAld) might be also operating, because aldehyde oxidases were up-regulated during clubroot formation (Ando et al 2006a). However, from transcriptome analysis there is no evidence that in Arabidopsis the corresponding genes are differentially expressed.…”

Isolation and Characterization of the Aldehyde Oxidase2 Gene from Arachis hypogaea L.

“…Plant AO belongs to a multigene family (Ando et al 2006;Min et al 2000;Ori et al 1997;Sekimoto et al 1997Sekimoto et al , 1998Zdunek-Zastocka 2008), whose members differ in electrophoretic mobility and subunit composition (Akaba et al 1999;Seo et al 2000b;Koiwai et al 2000;Omarov et al 2003;Zdunek-Zastocka et al 2004) and exhibit broad substrate specificity (Koiwai et al 2000;Akaba et al 1998). Plant AO has only been purified from coleoptiles of maize (Koshiba et al 1996).…”

Alternative transcription initiation of the nitrilase gene (BrNIT2) caused by infection with Plasmodiophora brassicae Woron. in Chinese cabbage (Brassica rapa L.)

“…These contradictory reports suggest that auxin biosynthesis must be affected in a complex manner during clubroot development. Indeed, several pathways of auxin biosynthesis and metabolism appear to be influenced by P. brassicae infection (Butcher et al 1974;Rausch et al 1981Rausch et al , 1983Searle et al 1982;Ludwig-Müller et al 1996;Ando et al 2006). Among such pathways, the routes for IAA biosynthesis via the formation of indole-3-acetaldoxime (IAOX) in Chinese cabbage and Arabidopsis (Ludwig- Müller andHilgenberg 1988, 1992), indole-3-methylglucosinolate (IMG) in Chinese cabbage (Helmlinger et al 1985), and indole-3-acetonitrile (IAN) in Chinese cabbage (Ludwig-Müller and Hilgenberg 1990) have been well studied in association with clubroot development.…”