Phytophthora infestans is a pathogenic oomycete that causes the infamous potato late blight disease. Resistance (R) genes from diverse Solanum species encode intracellular receptors that trigger effective defense responses upon the recognition of cognate RXLR avirulence (Avr) effector proteins. To deploy these R genes in a durable fashion in agriculture, we need to understand the mechanism of effector recognition and the way the pathogen evades recognition. In this study, we cloned 16 allelic variants of the Rpi-chc1 gene from Solanum chacoense and other Solanum species, and identified the cognate P. infestans RXLR effectors. These tools were used to study effector recognition and co-evolution. Functional and non-functional alleles of Rpi-chc1 encode coiled-coil nucleotide-binding leucine-rich repeat (CNL) proteins, being the first described representatives of the CNL16 family. These alleles have distinct patterns of RXLR effector recognition. While Rpi-chc1.1 recognized multiple PexRD12 (Avrchc1.1) proteins, Rpi-chc1.2 recognized multiple PexRD31 (Avrchc1.2) proteins, both belonging to the PexRD12/31 effector superfamily. Domain swaps between Rpi-chc1.1 and Rpi-chc1.2 revealed that overlapping subdomains in the leucine-rich repeat (LRR) domain are responsible for the difference in effector recognition. This study showed that Rpi-chc1.1 and Rpi-chc1.2 evolved to recognize distinct members of the same PexRD12/31 effector family via the LRR domain. The biased distribution of polymorphisms suggests that exchange of LRRs during host-pathogen co-evolution can lead to novel recognition specificities. These insights will guide future strategies to breed durable resistant varieties.
The potato tuber moth (Phthorimaea operculella Zeller) (PTM) is a destructive potato pest. Bacillus thuringiensis cry genes encode crystal proteins that have toxic characteristics against PTM. The aim of the present study was to develop a PTM resistant potato cv. Agria using the synthetic Bt cry1Ab gene. The transformation vector was constructed by inserting the cry1Ab gene into the pBI121 binary expression vector. The Agrobacterium tumefaciens strain AGL1 harboring the pBI35SCry1Ab construct was used for potato transformation. The results indicated that out of 97 putative transformed lines, 30 lines were PCR positive. Southern blot analysis revealed that one to three copies of transgenes were inserted into transgenic lines. The immunoassay test revealed the expression of the Cry protein. Furthermore, the results of bioassays confirmed the high mortality level of neonate larvae. The results of this study suggested that the transgenic lines have significant potential in pest control.
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