Abstract
Non-heading Chinese cabbage (Brassica rapa ssp. chinensis) is one of the main green leafy vegetables in the world, especially in China, with significant economic value. Hyaloperonospora parasitica is a fungal pathogen responsible for causing downy mildew disease in Chinese cabbage, which greatly affects its production. The objective of this study was to identify transcriptionally regulated genes during incompatible interactions between non-heading Chinese cabbage and H. parasitica using complementary DNA-amplified fragment length polymorphism (cDNA-AFLP). We obtained 129 reliable differential transcript-derived fragments (TDFs) in a resistant line ‘Suzhou Qing’. Among them, 121 upregulated TDFs displayed an expression peak at 24–48 h post inoculation (h.p.i.). Fifteen genes were further selected for validation of cDNA-AFLP expression patterns using quantitative reverse transcription PCR. Results confirmed the altered expression patterns of 13 genes (86.7%) revealed by the cDNA-AFLP. We identified four TDFs related to fungal resistance among the 15 TDFs. Furthermore, comparative analysis of four TDFs between resistant line ‘Suzhou Qing’ and susceptible line ‘Aijiao Huang’ showed that transcript levels of TDF14 (BcLIK1_A01) peaked at 48 h.p.i. and 25.1-fold increased in the resistant line compared with the susceptible line. Similarly, transcript levels of the other three genes, TDF42 (BcCAT3_A07), TDF75 (BcAAE3_A06) and TDF88 (BcAMT2_A05) peaked at 24, 48 and 24 h.p.i. with 25.1-, 100- and 15.8-fold increases, respectively. The results suggested that the resistance genes tended to transcribe at higher levels in the resistance line than in the susceptible line, which may provide resistance against pathogen infections. The present study might facilitate elucidating the molecular basis of the infection process and identifying candidate genes for resistance improvement of susceptible cultivars.
Highlights
It is well known that plant–pathogen interactions activate a subset of pathogen genes so-called systemic acquired resistance to protect themselves.[1,2,3] This interaction process is diverse and complicated because plant pathogens have evolved by developing various strategies to infect their hosts
Of the 121 transcript-derived fragments (TDFs) upregulated, 35 (28.9%), 31 (25.6%) and 4 (3.3%) TDFs were induced strongly at 24, 48 and 72 h.p.i., respectively; 12 (9.9%) and 2 (1.7%) TDFs were induced at 24 and 48 h.p.i., and 48 and 72 h.p.i., respectively. These results showed that non-heading Chinese cabbage has mainly accumulated expression at 24–48 h.p.i. and that gene expression patterns were different and complex after H. parasitica infection
By BLAST searching in the Brassica database, these TDFs were classified according to their different functions
Summary
It is well known that plant–pathogen interactions activate a subset of pathogen genes so-called systemic acquired resistance to protect themselves.[1,2,3] This interaction process is diverse and complicated because plant pathogens have evolved by developing various strategies to infect their hosts. Specific pathogen may trigger defense systems that are essential for pathogenicity. Molecular responses are up- or downregulations by numerous specific resistant genes. During the development of interaction, the recognition of specific host genes determines whether the interaction will be successful. Downy mildew is an important fungal disease of Brassica specie that is caused by the obligatory biotrophic oomycete Hyaloperonospora parasitica When downy mildew became epidemic, it can cause damage to 490% of the crop. The disease is more severe in spring and autumn seasons than in other seasons
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