Molecular characterization of NBS encoding resistance genes and induction analysis of a putative candidate gene linked to Fusarium basal rot resistance in Allium sativum.

摘要

Fusarium basal plate rot (FBR), caused by Fusarium oxysporum f. sp. cepae (FOC), is one of the most devasting soil-borne disease of onion and garlic (Allium sativum) worldwide. Resistance screening to FBR has resulted in identifying a garlic selection line CBT-As153 as resistant to FOC. Majority of plant disease resistance (R) genes encode a highly conserved nucleotide binding site and leucine-rich repeat structure (NBS-LRR) which can aid to isolate candidate genes linked to FBR resistance in CBT-As153. Degenerative primers based on the NBS conserved motif of NBS-LRR resistance proteins isolated 28 NBS sequences from CBT-As153 named as A. sativum resistance gene analogs (AsRGAs). Sequence analysis grouped the AsRGAs into six classes of non-toll interleukin receptor (non-TIR) subfamily. Quantitative real time polymerase chain reaction (qRT-PCR) revealed differential transcript expression of AsRGAs in stem, leaves and roots. AsRGA29, a putative RGA exhibited 20 fold higher expression of transcript levels in CBT-As153 than that of Allium fistulosum and Allium roylei, the two FBR resistant wild Allium species. Further, AsRGA29 showed significant induction in the transcript levels under FOC infection and treatment with four defense signaling molecules SA, MeJa, H₂O₂ and ABA. This suggests the critical involvement of AsRGA29 in mediating multiple defense signaling pathways towards protecting garlic against FOC. The present study will help in developing RGA based markers linked to FBR resistance in garlic and onion. Besides, it will also pave way towards future revelation of molecular mechanisms related to FOC resistance in CBT-As153.