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

Abstract

In clubroot disease, gall formation is induced by infection with the obligate biotroph Plasmodiophora brassicae, and cell hypertrophy is dependent on increased auxin levels. The enzyme nitrilase is suggested to play an important role in auxin biosynthesis in plants. Here, we investigated the expression of nitrilase genes in clubroot disease in Chinese cabbage (Brassica rapa L.). We isolated four isogenes of nitrilase (BrNIT1, BrNIT2, BrNIT3, and BrNIT4) from Chinese cabbage. When a BrNIT2-specific probe was used for Northern blot hybridization, enhanced accumulation of a 1.4 kb mRNA and additional shorter transcripts (1.1 kb) were only detected in clubbed roots 25 days postinoculation (dpi) onward. The expression of BrNIT1 was not strongly affected by infection with P. brassicae. BrNIT3 expression was detected in the roots at 10 and 20 dpi, and the expression was less in clubbed roots than in healthy roots at 20 dpi. Analysis of the transcription initiation point of the BrNIT2 gene suggests that 1.1 kb transcripts were generated by alternative transcription initiation between the second intron and the third exon. The sequence from the second intron to half of the third exon (+415 to +1037, 623 bp) had promoter activity in Arabidopsis during clubroot formation. Therefore, our results suggest that transcriptional regulation of BrNIT2 might be involved in auxin overproduction during clubroot development.

Hormonal Responses to Plasmodiophora brassicae Infection in Brassica napus Cultivars Differing in Their Pathogen Resistance

“…In Hornet galls, NIT1 transcription was up-regulated 35 dai, and especially at 49 dai (Figure 7). Our data are in accordance with several reports that describe the up-regulation of transcription of nitrilase isoforms in clubroot tissues compared to controls in different host plants such as Brassica rapa (turnip [29], Chinese cabbage [30]), or Brassica juncea [31], and specific expression of nitrilase 1 and 2 genes in developing galls of Arabidopsis thaliana , as well as with the up-regulation of myrosinases and glucosinolate metabolism [13,32,33]. The difference between IAA levels and the expression of IAA-biosynthetic genes may be given by the up-regulation of the expression of GH3 genes (encoding auxin conjugating enzymes), as was shown in the case of Arabidopsis thaliana [26].…”

How Pathogens Affect Root Structure

“…In Arabidopsis, genes involved in auxin synthesis, transport, and responses are strongly upregulated. Regulation of nitrilase genes involved in auxin synthesis has also been reported in B. rapa (Ando et al 2008). The alh1 mutant of Arabidopsis, which may be affected in auxin transport, shows resistance responses to P. brassicae (Devos et al 2006).…”

Multi-Omics Approaches to Improve Clubroot Resistance in Brassica with a Special Focus on Brassica oleracea L.

“…rapa ssp. pekinensis Isolate Ibaraki-1 Roots 10, 20, 25, 30, 35 and 40 dpi Expression analysis of nitrilase genes ( BrNIT2 ) suggested that 1.1 kb transcripts might be involved in auxin overproduction during clubroot development [ 237 ] B . rapa ssp.…”