Expression analysis of genes associated with sucrose accumulation and its effect on source-sink relationship in high sucrose accumulating early maturing sugarcane variety.

Sucrose synthesis/accumulation in sugarcane depends on the source-sink communication wherein source responds to sink demand for photoassimilate supply. Sucrose in stalk (sink) acts as signal, and sends feedback to restrain further synthesis of sucrose by regulating photosynthetic efficiency of leaves (source). Hence sucrose synthesis/accumulation is controlled by many genes and regulatory sequences including 3 invertases (SAI, CWI, NI), sucrose synthase (SuSy) and sucrose phosphate synthase (SPS). SPS and invertase play key role in enhancing sink strength which ultimately promotes greater sucrose accumulation in the sink tissues. In present study, a significant positive correlation was found between sucrose% of source and sink tissues which was greater in the top (R 2 = 0.679) than middle (R 2 = 0.580) and bottom (R 2 = 0.518) internodes, depicting that sucrose accumulation in the stalk bears a direct relation with sucrose translocation efficiency from source. Results indicated an increased sucrose% with maturity, while reducing sugar content decreased with crop growth. qRT-PCR results exhibited an elevated expression of invertase in immature sink tissues depicting increased sink requirement, which declined with maturity. Similarly, increased PEP carboxylase gene expression as observed supported the fact that higher sink demand results in enhanced photosynthetic rate and thus influences the source activity. SPS was found active at initial stage of cane development indicating its role in sucrose synthesis. Thus by studying expression patterns of the different genes both, in source and sink tissues, a better understanding of the sucrose accumulation pathway in sugarcane is possible, which in turn can help in elucidating ways to enhance sucrose concentration in sink.