Association of Alternaria brassicicola induced NAC transcription factors with desiccation and wound responses in Indian mustard

Plants have evolved a specific class of transcription factors (TF) known as NAC TFs (NAM, ATAF and CUC), which have diverse functions including responses to abiotic and biotic stresses. To understand the role of NAC TFs in plant defence response against 'Black Spot' disease caused by Alternaria brassicicola in oilseed mustard (Brassica juncea), the NAC TFs identified from transcriptome data of non-host resistant Sinapis alba challenged with the pathogen were used, since no complete resistant variant of oilseed mustard is available. Subsequent phylogenetic analysis of the 38 NAC TFs, identified from S. alba and the corresponding NAC sequences from B. juncea clustered the NAC TFs into 4 groups. Upon challenge with A. brassicicola, expression dynamics of 13 selected NAC TFs led to the identification of 6 NAC TFs (NAC19, NAC36, NAC55, NAC62, NAC72, and NAC81) which were signifi-cantly induced in resistant S. alba, ABA (abscisic acid) treated B. juncea B85 (which gives tolerance) and Alternaria tolerant B. juncea (PAB9511), compared to susceptible B. juncea (B85). Further study revealed that the selected NACs were induced upon desiccation and/or wound treatment as well as by methyl-jasmonate, indicating a mutually shared function of these NACs in both abiotic and biotic stresses in B. juncea and S. alba. Finally, our data support that these NACs despite being evolutionarily conserved in mediating desiccation and wound response among B. juncea and S. alba, show variation in early signalling upon recognition of the pathogen, which is a major issue for differential expression of these genes.