Studies on time-course expression of defence genes in banana against Pratylenchus coffeae for the creation of a subtractive cDNA library.

Abstract

Identification of genes that confer nematode resistance is important for banana improvement. These can either be used as molecular markers for markerassisted selection or directly by guiding the design of transgenic plants with high resistance. Cultivars with differential reaction to nematode infection and knowledge of time-course expression of defence genes after nematode infection are a prerequisite for the isolation of resistance genes in banana through functional genomics. Based on pot culture screening and biochemical studies, cultivars 'Karthobiumtham' (ABB) and 'Nendran' (AAB) were identified as resistant and susceptible, respectively, to the root-lesion nematode Pratylenchus coffeae. The semiquantitative RT-PCR analysis revealed that mRNA levels of the chalcone synthase gene, the first enzyme in the pathway for flavonoid biosynthesis, was constitutively higher in roots of resistant 'Karthobiumtham' than in the susceptible 'Nendran'. The transcript level of this defence gene was found to increase up to 6 days after nematode inoculation (DAI) and start declining from 7 DAI onwards in both resistant as well as susceptible root samples. From these preliminary studies, it is inferred that for identifying and isolating differentially expressed genes due to nematode infestation, a subtractive library of the interaction of Musa with P. coffeae should be created by subtracting the cDNA of uninoculated root samples from cDNA of inoculated root samples within 6 DAI. A cDNA library is being created through Suppression Subtractive Hybridisation (SSH) for isolating the genes that are differentially activated during the nematode-host interactions.