Metabolic Changes Associated with the Development of Yellow Canopy Syndrome in Sugarcane

Yellow Canopy Syndrome (YCS) was first observed in 2012 and is still an undiagnosed condition affecting the Central and Northern cane-growing regions in Australia.  The development of YCS is distinctly different from that of Sugarcane Yellow Leaf Virus (SCYLV). We are doing comprehensive metabolome and transcriptome analyses to reconstitute the metabolic pathways in the leaves and sink tissues during the development of YCS.  This is to pinpoint the specific reactions that lead to the expression of YCS.  The data show that metabolism is compromised throughout the canopy, and in leaves even where there is no visual expression of YCS.  The metabolic changes that are observed include a huge increase in soluble sugars, an uncoupling of electron transport activity and a suppression of photosynthesis.  The large increase in sucrose levels is consistent with a disruption of phloem loading or suppression of sink strength.  In addition, three other metabolic changes could be very important.  Firstly, we see significant levels of metabolites that are indicative of microorganisms that normally associate with injured tissue, especially where there are significant available carbohydrates.  Secondly, there are significant increases in several caffeoyl/chlorogenic type compounds which are indicative of wounding and activation of plant defence systems. Thirdly, we find increases in certain amino acids and metabolites that are indicative of stress metabolism and indications of a disruption of the electron transport system, which is highly dependent on fast turnover of protein components.  These findings will be discussed in relation to alterations in the transcriptome during YCS development.