A Mapped Locus on LG A6 of Brassica juncea Line Tumida Conferring Resistance to White Rust Contains a CNL Type R Gene

Abstract

White rust, causal agent oomycete Albugo candida, is a significant disease of the cultivated Brassica species. The Indian gene pool lines of oilseed mustard, Brassica juncea, are highly susceptible to the pathogen. Resistance to A. candida has been reported in the east European gene pool lines of mustard and mapped to LG A4 in line Heera and LG A5 in line Donskaja-IV. A new resistance-conferring locus to A. candida isolate AcB1 has been mapped to LG A6 of B. juncea line Tumida-a Chinese vegetable type mustard using an F 1 DH mapping population that has been developed from a Tumida × Varuna (susceptible Indian gene pool line) cross. A molecular map containing 8,303 genic and GBS markers was used to map the resistance trait to an interval of 63.0 cM-70.8 cM on LG A6. Genome assemblies of Tumida and Varuna were used to find the genes present within the flanking markers discerned by genetic mapping. The most likely candidate gene in the mapped interval is BjuA046215, a CC-NBS-LRR (CNL) type R gene that encodes a protein with all the specific subdomains of the proteins encoded by such genes. Alleles of BjuA046215 in Varuna and other lines of the Indian and the east European gene pools encode proteins that have truncated LRR domains. Analysis of the syntenic regions in some of the Brassicaceae genomes and phylogenetic analysis of CNL type R genes showed BjuA046215 to be closely related to a recently described white rust resistance-conferring R gene BjuWRR1 in B. juncea Donskaja-IV, both belonging to the CNL-D group of R genes. Related R genes in Arabidopsis thaliana confer resistance to another oomycete, Peronospora parasitica.

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

“…Several QTL have been mapped in the Indian and east European gene pool lines (Dhaka et al ., 2017; Rout et al ., 2018). The Chinese vegetable types like Tumida constitute another divergent gene pool (Yang et al ., 2016) that contains potentially useful traits like serrated leaves, basal branching (Muntha et al ., 2018) and disease resistance (Bhayana et al ., 2019). The highly contiguous genome sequence assembly of B. juncea Varuna will allow fine mapping in the QTL regions, identification of the candidate genes, and understanding the molecular mechanisms underlying some of the critical quantitative traits, thereby strengthening mustard breeding in south Asia and other parts of the world.…”

Using wild relatives and related species to build climate resilience in Brassica crops

“…Resistance to white rust (WR) caused by the pathogen Albugo candida has been found in B. juncea, B. napus, B. rapa and B. carinata varieties (Panjabi-Massand et al 2010 ; Awasthi et al 2012 ). Quite recently, a B. juncea Chinese vegetable type mustard called Tumida was found to be resistant to WR, for which a responsible locus was located on linkage group A06 (Bhayana et al 2020 ). Different Brassica genotypes and allies from diverse origins were tested against Pseudocercosporella capsellae (white leaf spot disease) in field and/or controlled conditions, and genotypes from B. carinata, B. juncea, B. napus, B. oleracea and B. fruticulosa shown to be highly resistant (Gunasinghe et al 2014 , 2017 ).…”

Current Status of the Disease-Resistant Gene(s)/QTLs, and Strategies for Improvement in Brassica juncea

“…Tumida (resistant) × B. juncea var. Varuna (susceptible) was identified with a new white rust resistance-conferring locus on LG A6 which was most likely to BjuA046215 candidate gene, a CC-NBS-LRR type R gene, and closely related to BjuWRR1 ( Bhayana et al, 2020 ).…”

“…The host resistance was reported to be governed by a single locus on LG A4, LG A5, and LG A6 in Heera, Donskaja-IV, and Tumida lines of B. juncea , respectively. However, the resistant genes conferring resistance in these loci were found closely related to R gene BjWRR1 ( Bhayana et al, 2020 ). It will be beneficial for molecular studies to identify the hosts conferring resistance against a broadspectrum of pathogens i.e.…”