Exploration of cotton leaf curl virus resistance genes and their screening in Gossypium arboreum by targeting resistance gene analogues

Abstract

Cotton leaf curl virus (CLCuV) disease is one of the major limiting factors in cotton production, particularly in widely cultivated Gossypium hirsutum varieties that are susceptible to attack by this virus. Several approaches have been employed to explore putative resistance genes in another cotton species, G. arboreum. However, the exact mechanisms conferring disease resistance in cotton are still unknown. In the current study, we used various approaches to identify possible resistance genes against CLCuV infection. We report the identification and isolation of a set of genes involved in the resistance response to viral infestation. PCR products containing genomic DNA gave multiple amplifications with a single primer in most reactions, and 38 fragments were cloned from G. arboreum and G. hirsutum. The sequences of cloned fragments belonged to various pathway genes and uncharacterized proteins. However, five amplified fragments (RM1, RM6, RM8, RM12 and RM31) showed similarity with R genes. Maximum homology (94 %) was observed with G. raimondii toll/interleukin receptor-like protein. BLAST search showed the homology of all resistance gene analogues (RGAs) with more than one chromosome, and multiple hits were observed on each chromosome for each RGA. Expression analysis through RT–PCR identified variable expression levels of the different RGAs in all tested genotypes. The expression level of RGAs differed between symptomatic and asymptomatic plants, with the exception of RGA 395, whose expression level was the same in both diseased and healthy plants. Knowledge of the interaction of these genes with various cotton pathogens could be utilized to improve the resistance of susceptible G. hirsutum and other plant species.

Abstract

The cotton species, Gossypium hirsutum, is sensitive to attack by cotton leaf curl virus. The devastating virus attacks the cotton plant when it gets a chance to get into the system, consequently resulting in curling of the leaves. Whitefly serves as a viral vector, and when feeding on the cotton plant, break the protective barrier and hence result in cotton infestation. Another species of cotton, Gossypium arboreum, is totally resistant to this viral disease. Whitefly also feed on G. arboreum and transmit virus, but this species has a natural defence system that does not allow the virus to cause infection and disease. The present study identified some genes of the defence system of G. arboreum that might contribute to make this species resistant to leaf curl disease in cotton.