Castor (Ricinus communis L.) Rc-LOX5 plays important role in wilt resistance

Phyto-oxylipins are a group of biologically active molecules that play an important role in plant defense. Their production begins with the oxygenation of polyunsaturated fatty acids by lipoxygenases (LOXs; EC 1.13.11.12) to form 9- or 13-hydroperoxides. These are substrates for several enzymes involved in the synthesis of final oxylipins, which can act as signal molecules and/or direct antimicrobials. Recent completion of the castor bean genome sequence now permits genome-wide analysis of the LOX gene family in castor as well as comparison with LOX in Arabidopsis. We identified 12 candidate LOX genes in the castor bean genome. Phylogenetic analysis indicated that these LOX members cluster into two groups, designated types 1 and 2, as expected from previous studies. Out of which six LOX gene specific primers were designed to amplify castor LOX genes i.e. LOX1, LOX2, LOX3, LOX4, LOX5 and Dox. Sequence analysis showed conserved five iron binding sites in the LOX domain of all the Rc-LOX, however, only LOX5 contained consensus (positions 547, 556, and 715) histidines residue. Expression analysis of LOX2, 3, 4, 5 and DOX genes in resistant and susceptible genotypes of castor at 0 days after infection (DAI), 5 DAI and 10 DAI (30 days after sowing) was carried out using quantitative real time (RT)-PCR during castor bean–Fusarium oxysporium f. sp. ricini interaction. Results suggest that 2 (LOX2 and LOX5) of 6 Rc-LOX genes were detectable. Resistant genotypes (48-1 and SKP-84) exhibited appreciably higher expression of LOX5 during castor bean–F. oxysporium interaction, which further suggest the participation of Rc-LOX5, a type-1 LOX predicted to be 9-LOX, in wilt resistance.

► Six LOX genes of castor were sequenced.
► All genes showed more than 95% similarity on NCBI with previous sequences.
► Expression analysis of LOX genes showed higher expression of LOX2 and LOX5 in resistant genotypes.
► Only LOX5 (9-LOX) showed conserved histidine residue at positions 547, 556, and 715 in amino acid sequence of gene.
► Dendrogram based on sequence analysis showed LOX5 laid on separate cluster which further confirmed the distinct function of LOX5 in disease resistance.