BjuWRR1, a CC-NB-LRR gene identified in Brassica juncea, confers resistance to white rust caused by Albugo Candida

Abstract

a CC-NB-LRR gene identified in Brassica juncea, confers resistance to white rust 36 caused by Albugo candida 37 Running title 38 A CNL type R gene confers white rust resistance in B. juncea 39 Highlight 40 BjuWRR1, a CNL type R gene, was identified from an east European gene pool line of 41 Brassica juncea and validated for conferring resistance to white rust by genetic 42 transformation. 43 Abstract 44 White rust caused by oomycete pathogen Albugo candida is a significant disease of crucifer 45 crops including Brassica juncea (mustard), a major oilseed crop of the Indian subcontinent. 46Earlier a resistance-conferring locus named AcB1-A5.1 was mapped in an east European 47 gene pool line of B. juncea  Donskaja-IV. This line was tested along with some other lines 48 of B. juncea (AABB), B. rapa (AA) and B. nigra (BB) for resistance to six isolates of A. 49 candida collected from different mustard growing regions of India. Donskaja-IV was found 50 to be completely resistant to all the tested isolates. Sequencing of a BAC spanning the locus 51 AcB1-A5.1 showed the presence of a single CC-NB-LRR protein encoding R gene. The 52 genomic sequence of the putative R gene with its native promoter and terminator was used 53 for the genetic transformation of a susceptible Indian gene pool line Varuna and was found to 54 confer complete resistance to all the isolates. This is the first white rust resistance-conferring 55 gene described from Brassica species and has been named BjuWRR1. Allelic variants of the 56 gene in B. juncea germplasm and orthologues in the Brassicaceae genomes were studied to 57 understand the evolutionary dynamics of the BjuWRR1 gene. 58 Introduction 61White rust, caused by an oomycete pathogen Albugo candida (Pers.) Kuntze is a serious 62 disease of economically important Brassica species. A. candida is an obligate biotrophic 63 parasite and rated amongst the top ten oomycete pathogens based on its scientific and 64 economic importance (Kamoun et al., 2015). White rust has been reported to cause 65 A. candida isolates, infection and disease evaluation 129 5White rust infected B. juncea leaves were collected from five different mustard growing 130 regions of north India (Pantnagar, Meerut, Samastipur, Hisar and Alwar) and were purified 131 by performing five passages of inoculations for each isolate on a susceptible B. juncea line, 132Varuna. In each passage, zoosporangia collected from a single pustule were suspended in 200 133 L of sterilized double distilled water followed by drop inoculation on cotyledons of seven-134 day-old seedlings of Varuna. Inoculations were performed in a contained white rust infection 135 chamber maintained at a relative humidity of around 90% and 18°C of temperature with a 16-136 h light/8-h dark cycle. After repeated passages of single pustules, the isolates were 137 maintained on Varuna and the purified A. candida isolates were named as AcP1 (Pantnagar), 138

A chromosome-scale assembly of allotetraploid Brassica juncea (AABB) elucidates comparative architecture of the A and B genomes

“…The east-European lines, as such, are ill-adapted to the growing conditions in South Asia due to photoperiod sensitivity but contain a large number of positive traits like high pod density [38][39][40] , oil and seed meal quality [41][42] , and disease resistance 43 . Several QTL have been mapped in the Indian and East European gene pool lines [38][39][40][41][42][43][44] . The Chinese vegetable types like Tumida constitute another divergent gene pool 5 that contains potentially useful traits like serrated leaves, basal branching 45 , and stem strength.…”

A highly contiguous genome assembly of Brassica nigra (BB) and revised nomenclature for the pseudochromosomes

“…This lack of pairing, in all probability, is due to a very divergent chromosomal organization between the B, and A/C genomes. Genetic exchanges may also be limited due to a strong mechanism in the B genome for suppression of pairing between the homeologous chromosomes [ 33 , 34 ].…”

Genomic and Molecular Perspectives of Host-pathogen Interaction and Resistance Strategies against White Rust in Oilseed Mustard

“…The genome of B. juncea variety Tumida and B. juncea variety Varuna has been sequenced [ 77 ]. Further analysis of the sequences will enable us to identify S genes responsible for WR infection in the host tissue.…”

“…Gene BjuWRR1 from Donskaja IV, encoding a CNL domain-containing protein has been identified to confer WRR. The transgenic B. juncea variety Varuna constitutively expressing BjuWRR1 conferred WRR to various isolates of A. candida [ 77 ].…”

“…Specifi c activation of TNL & CNL receptor by A. candida effectors triggers ETI. Few TNL genes are identified, for example, RAC1, WRR4A, WRR4B, WRR8, WRR9, and WRR12 reported in Aradopsis [ 30 ]; CNL genes, for example, BjuWRR1 in Donskaja IV, is an east European variety of B. juncea [ 77 ]. All the TNLs signal via NRG1 and some can also signal via ADR1.…”