Is ferritin involved in resistance to common scab? - CLICK FOR VIDEO
Soil-borne actinobacterium Streptomyces scabiei causes potato common scab posing a worldwide threat in terms of reduction in quality and market value of infected tubers. This bacterium secretes a phytotoxin, thaxtomin A (TA), which is required for the development of disease symptoms characterized by corky lesions on tuber surface. Our laboratory developed common scab resistant somaclones (YG8 and YG32) by habituating Yukon Gold (YG) somatic cells to TA. Proteomic analyses of YG8 and YG32 tubers revealed the higher abundance of two ferritin proteins i.e., Q9SWS0 and M1AH14 when compared to YG tubers. Ferritins are iron storage proteins that maintain iron homeostasis. Higher expression of chloroplastic ferritin-3 gene was confirmed in mature YG8 and YG32 tubers compared to YG tubers. Moreover, ICP-MS analyses showed 1.5-2 times higher iron content in YG8 and YG32 tubers than in YG tubers. Since plants and pathogens may compete for iron during infection, it is possible that iron sequestration in YG8 and YG32 tubers may reduce iron availability to pathogens, thus decreasing S. scabiei infection. Hence, we speculated that enhanced abundance of ferritin in resistant somaclones may contribute to increasing resistance to common scab. This was supported by results obtained in another TA-habituated variety, Kennebec, where the ferritin-3 chloroplastic gene showed 4 times higher expression in tubers from TA-habituated and common scab resistant somaclone K-39 when compared to parental Kennebec. To further investigate the role of ferritin and iron during pathogen infection, minitubers from Yukon Gold were infected with S. scabiei in the presence or absence of an iron chelator (siderophore). Results will be presented on the quantification of ferritin gene expression and iron levels as well as the evaluation of common scab symptoms under these conditions. Collectively, these results will help us understand the involvement of ferritin and iron in common scab resistance.