Yellow Canopy Syndrome Is Associated with Changes in Primary and Secondary Metabolism

Yellow Canopy Syndrome (YCS) is a condition affecting sugarcane in Australia, of which the cause has not been identified. The YCS phenotype is yellowing of the mid-canopy leaves. Previously we showed that photosynthesis and transpiration are suppressed on a canopy-wide level and that sugar levels are significantly increased in the symptomatic and asymptomatic leaves. It is well known that increased sucrose levels in leaves can lead to a suppression of photosynthesis and leaf yellowing in the Poaceae. This study is focused on understanding the mechanisms through which YCS development alters sucrose accumulation, and the effect of sucrose on leaf metabolism. For this purpose, in-depth analyses of the transcriptome, proteome and metabolome are used. Several recent advances in plant sciences have flowed from an omics-integration approach. Such an approach provides a more complete picture of the plant cellular state than studies using just one set of omics data. The results of this study show YCS-symptomatic leaves had perturbed metabolism in four key areas: sugar metabolism, pentose phosphate cycle, phenylpropanoid metabolism, and α-ketoglutarate metabolism. Lower abundance of photosynthetic and chloroplastic proteins were found in the leaf, coupled with an increase of cellular respiration-component proteins of the mitochondria and cytosol. There was a notable increase in chaperone/heat shock proteins. Transcriptomic studies additionally showed transcription regulation, protein turnover and signal transduction pathways were impacted. Through these data, and identification of affected molecular pathways, a deeper understanding of the YCS phenotype, and sucrose leaf metabolism during stress, is reached.