Alteration of Genetic Make-up in Karnal Bunt Pathogen (Tilletia indica) of Wheat in Presence of Host Determinants.

Alteration of genetic make-up of the isolates and monosporidial strains of Tilletia indica causing Karnal bunt (KB) disease in wheat was analyzed using DNA markers and SDS-PAGE. The generation of new variation with different growth characteristics is not a generalized feature and is not only dependant on the original genetic make up of the base isolate/monosporidial strains but also on interaction with host. Host determinant(s) plays a significant role in the generation of variability and the effect is much pronounced in monosporidial strains with narrow genetic base as compared to broad genetic base. The most plausible explanation of genetic variation in presence of host determinant(s) are the recombination of genetic material from two different mycelial/sporidia through sexual mating as well as through para-sexual means. The morphological and development dependent variability further suggests that the variation in T. indica strains predominantly derived through the genetic rearrangements.

Cloning, in silico characterization and induction of TiKpp2 MAP kinase in Tilletia indica under the influence of host factor(s) from wheat spikes.

In order to understand the molecular mechanism(s) associated with floret specificity, morphogenetic and disease development of Karnal bunt (KB) pathogen in wheat spikes, host factor(s) was isolated from KB prone susceptible stage of wheat spikes. An orthologue of Kpp2 gene involved in pheromone response and fungal development was isolated from Tilletia indica for analyzing its role in fungal development. The maximum expression of TiKpp2 gene was observed at 14th day and decreased thereafter. To investigate whether the fungus alters the expression levels of same kinase upon interaction with plants, T. indica cultures were treated with 1% of host factor(s). Such treatment induced the expression of TiKpp2 gene in time dependent manner. Host factor(s) treatment tends to increase the myelination in fungal cultures by lowering the sporidial production. Increase in myelination led to impose more pathogenicity levels in the host and prolific multiplication of pathogen inside host causing more damage to developing grains. In silico characterization and protein-protein interaction studies further suggests that isolated gene showed similarity with Ustilago maydis Kpp2 and induction of TiKpp2 might further activate a downstream transcription factor Prf1. The results of present study clearly suggest that host factor(s) derived from wheat spikes provide certain signal(s) which activate TiKpp2 gene during morphogenetic development of T. indica and affect the fungal growth and pathogenicity. In turn it also provides a plausible explanation for floret specificity of KB fungus in wheat.

Induction of MAP kinase homologues during growth and morphogenetic development of Karnal bunt (Tilletia indica) under the influence of host factor(s) from wheat spikes.

Signaling pathways that activate different mitogen-activated protein kinases (MAPKs) in response to certain environmental conditions, play important role in mating type switching (Fus3) and pathogenicity (Pmk1) in many fungi. In order to determine the roles of such regulatory genes in Tilletia indica, the causal pathogen of Karnal bunt (KB) of wheat, semi-quantitative and quantitative RT-PCR was carried out to isolate and determine the expression of MAP kinase homologues during fungal growth and development under in vitro culture. Maximum expression of TiFus3 and TiPmk1 genes were observed at 14th and 21st days of culture and decreased thereafter. To investigate whether the fungus alters the expression levels of same kinases upon interaction with plants, cultures were treated with 1% of host factors (extracted from S-2 stage of wheat spikes). Such treatment induced the expression of MAPks in time dependent manner compared to the absence of host factors. These results suggest that host factor(s) provide certain signal(s) which activate TiFus3 and TiPmk1 during morphogenetic development of T. indica. The results also provides a clue about the role of host factors in enhancing the disease potential due to induction of MAP kinases involved in fungal development and pathogenecity.