Abstract
Mustard aphid, Lipaphis erysimi (L.) Kaltenbach is a perpetual annual threat in the cultivation of rapeseed- mustard (Brassica spp.) crop in tropical and sub-tropical climate. Cultivated Brassica germplasm has failed so far to provide any source of resistance. Wild germplasm is a potential source of resistance against many threatening herbivores. On wild germplasm screening, we noted that the wild crucifer Rorippa indica (L.) Hiern confers resistance against L. erysimi. In the present study L. erysimi challenged transcriptome of R. indica was compared to un-infested R. indica sample to get a molecular insight about the aphid resistance mechanism and identify the candidate defense response genes. Cloning, sequencing and in silico sequence analysis of complimentary DNA amplified fragment length polymorphism identified 116 differentially expressed transcript derived fragments revealed thirty candidates which are from different functional categories including redox regulation, signalling, photosynthesis, structure, metabolism, defense response as well as a few of unknown function. Twenty four identifications were then studied by quantitative real time RT PCR analysis at 6, 12, 24 and 48 hour time point post infestation to understand the early-to-late defense response through their relative gene expression profiles. Seventeen fragments showed significant up or down regulation at p<0.05 level. The response was influenced by different phytohormonal signalling pathways simultaneously. The candidate defense response expressed sequence tags specifically for the resistance genes identified in this study have implication in building desired mustard aphid resistance in susceptible rapeseed-mustard plants in future. This is the first molecular report on crucifer defense response against mustard aphid L. erysimi.
Highlights
Rapeseed-mustard (Brassica spp.) is the third most important oilseed crop after soybean (Glycine max) and palm (Elaeis guineensis) in world agriculture and India is the third largest producer with global contribution of 28.3% acreage and 19.8% production
In the present study we aim to identify the candidate defense response gene(s) from L. erysimi resistant wild crucifer R. indica
The present study reports the up regulation of transcript derived fragments (TDFs) for EDM2 (AT5G55390), the transcriptional regulator for RPP7, up to 1.93 fold by 24 hpi and 1.61 fold at 48 hpi
Summary
Rapeseed-mustard (Brassica spp.) is the third most important oilseed crop after soybean (Glycine max) and palm (Elaeis guineensis) in world agriculture and India is the third largest producer with global contribution of 28.3% acreage and 19.8% production. Lipaphis erysimi (L.) Kaltenbach (Homoptera: Aphididae) is one of the most devastating pests of B. juncea. These tiny intruders are mostly visible at the flowering stage affecting the crop yield severely every year in terms of both quality and quantity [1,2]. They are crucifer specialist like the more studied one Brevicoryne brassicae (cabbage aphid), but work best in the tropical climate on the oilseed Brassicas. Instead they sequester plant glucosinolates and synthesise their own myrosinases for their own defense [4]
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