The soybean -Phytophthora sojae interaction

The major goal of the lab is to understand the molecular basis of the soybean-P. sojae interaction. As a first step towards understanding the interaction the lab has applied a map-based cloning strategy and isolated the disease resistance gene Rps1-k (Gao et al. 2005; Bhattacharyya et al. 2005; H. Gao and M.K. Bhattacharyya, unpublished).

They have applied a yeast two-hybrid approach in isolating Rps1-k-intarcting proteins to better understand the signaling factors involved in the expression of Phytophthora resistance. They have shown that GmMcII encoding a type II metacaspase interacts with Rps1-k-2 (H. Gao and M.K. Bhattacharyya, unpublished). Presumably, GmMcII regulates programmed cell death requires for expression of Phytophthora resistance.

They have applied a phosphoproteomics approach in order to identify the soybean proteins that are differentially phosphorylated following P. sojae infection. Many of the defense-related proteins are phosphorylated in this plant-pathogen interaction (R. Saravanan and M.K. Bhattacharyya, unpublished).

Recently they have applied the 454-sequencing (pyro-sequencing) technology to determine the steady state transcript levels of both soybean and P. sojae genes in the resistant and susceptible responses following P. sojae infection of etiolated soybean hypocotyls. In collaboration with Dr. Steven Cannon, they are able to show that many novel genes are induced in this plant pathogen interaction. This approach allows to provide a better estimate of the global transcript profiles, because transcripts are sequenced. Many novel transcripts, not included in microarray analyses, will be identified through this high throughput sequencing project.

Bhattacharyya expects that through application of the multiple molecular biological approaches in studying this model plant-pathogen interaction they will be able to develop novel biotechnological strategies to fight not only P. sojae, but also other soybean pathogens. He hopes that their effort will significantly contribute towards securing sustainable productivity of this very important legume crop.

The Soybean-Fusarium virguliforme Interaction.

In recent years, soybean has been increasingly attacked by the fungal pathogen F. virguliforme that causes sudden death syndrome (SDS). At present, efforts to identify desirable Fusarium resistant soybean lines have not been successful. In the field conditions, resistance is partial. This pathogen produces at least two phytotoxins. Presumably, these toxins are involved in causing SDS. By applying a proteomic approach, the Bhattacharyya group has shown that ribulose 1,5-bisphosphate carboxylase/oxygenase large subunit is degraded in diseased tissues. Light is essential for initiating the disease (Ji et al. 2006). Bhattacharyya group has purified the putative toxin and raised monoclonal antibodies against this toxin. Reecently they have cloned the toxin gene and showed that expression of the gene in soybean leaves using a SMV-based vector resulted in SDS-like foliar symptoms (H. Brar and M.K Bhattacharyya, unpublished). They plan to use this toxin protein in a yeast two-hybrid sytem in isolating the host factor that is involved in causing the SDS foliar symptoms.

Arabidopsis nonhost resistance against the soybean pathogen, Phytophthora sojae

Arabidopsis is totally immune to P. sojae. The Bhattacharyya lab has showed that single cells of Arabidopsis mutant, pen1.1, are invaded by the pathogen. Mutation in a syntaxin protein led to loss of normal vesicle mediated free radical transport to the infection site for nonhost resistance in pen1-1 (Collins et al. 2003). The Bhattacharyya group created an ethyl methane sulfonate-induced mutant population in pen1.1. Currently they are screening the mutant population to identify mutants that are invaded by P. sojae to multiple cell layers. They have identified several putative mutants that are homozygous susceptible. They plan to map and clone several of the Arabidopsis genes that confer nonhost resistance against P. sojae. The group will then investigate if homologues of these genes are absent in soybean or expression patterns of these gene in soybean are differentas compared to that in Arabidopsis. Eventually they would like to engineer soybean for immunity observed in Arabidopsis against this pathogen.