Identification of candidate genes involved in Witches' broom disease resistance in a segregating mapping population of Theobroma cacao L. in Brazil.

BACKGROUND: Witches' broom disease (WBD) caused by the fungus Moniliophthora perniciosa is responsible for considerable economic losses for cacao producers. One of the ways to combat WBD is to plant resistant cultivars. Resistance may be governed by a few genetic factors, mainly found in wild germplasm. RESULTS: We developed a dense genetic linkage map with a length of 852.8 cM that contains 3,526 SNPs and is based on the MP01 mapping population, which counts 459 trees from a cross between the resistant 'TSH 1188' and the tolerant 'CCN 51' at the Mars Center for Cocoa Science in Barro Preto, Bahia, Brazil. Seven quantitative trait loci (QTL) that are associated with WBD were identified on five different chromosomes using a multi-trait QTL analysis for outbreeders. Phasing of the haplotypes at the major QTL region on chromosome IX on a diversity panel of genotypes clearly indicates that the major resistance locus comes from a well-known source of WBD resistance, the clone 'SCAVINA 6'. Various potential candidate genes identified within all QTL may be involved in different steps leading to disease resistance. Preliminary expression data indicate that at least three of these candidate genes may play a role during the first 12 h after infection, with clear differences between 'CCN 51' and 'TSH 1188'. CONCLUSIONS: We combined the information from a large mapping population with very distinct parents that segregate for WBD, a dense set of mapped markers, rigorous phenotyping capabilities and the availability of a sequenced genome to identify several genomic regions that are involved in WBD resistance. We also identified a novel source of resistance that most likely comes from the 'CCN 51' parent. Thanks to the large population size of the MP01 population, we were able to pick up QTL and markers with relatively small effects that can contribute to the creation and selection of more tolerant/resistant plant material.

Two subtilisin-like proteases from soybean.

Two subtilisin-like proteases (SLP) were identified in soybean (Glycine max [L.] Merr.). The first, SLP-1, was localized in seed coats early in seed development, but became undetectable with anti-SLP-1 antibodies as seed fill progressed. A partial purification of SLP-1 was achieved using a two step chromatographic procedure. NH2-terminal sequence analysis of the partially purified enzyme permitted primers to be designed that were used to amplify cDNA encoding SLP-1. A genomic clone encoding SLP-1 was also obtained. Characterization of the cDNA and partially purified SLP-1 revealed the initial translation product was an 82 694 MW precursor. After removal of a signal peptide, the mature protein was formed by removal of an NH2-terminal propeptide. A COOH-terminal peptide also appeared to be removed from some of the protease molecules. DNA blot analysis suggested that at least one additional SLP gene was present in soybean. The second gene, SLP-2, was subsequently cloned and characterized. Although the coding regions for SLP-1 and SLP-2 were homologous, their promoters were quite divergent. RT-PCR revealed that SLP-2 message was found in the mature plant and in cotyledons of germinating seeds. Although SLP-2 mRNA could be identified in developing seeds, the message was at least an order of magnitude less abundant than that for SLP-1, and it was mis-spliced such that a chain termination event would preclude obtaining a product. As with SLPs from other organisms, the functions of the soybean proteases are unknown. However, SLP-1 is one of only a few proteins from soybean seed coats that have been described.