Molecular regulation of sink-source transition in rice leaf sheaths during the heading period

摘要

The upper leaf sheath of rice (Oryza saliva L.) serves as a temporary starch sink before heading, subsequently becoming a carbon source tissue to the growing panicle at the post-heading stage. The time of sink-source transition in upper leaf sheaths is highly correlated to the panicle exsertion. Here, we found that the expression profiles of starch synthesis genes such as ADP-glucose pyrophosphorylase large subunit 2, granule-bound starch synlhase II, soluble starch synthase I, starch branching enzyme (SBE) I, SBE11I, and SBEIV were highly correlated with starch content changes during the heading period in the second leaf sheath below the flag leaf. In addition, the ot.-amylase2A and fi-amylase were considered as major genes that were in charge of starch degradation at the post-heading period. Of the five sucrose transporter (OsSUT) genes, OsSUTl and OsSUT4 appeared to play an important role in sucrose loading into the phloem of source leaf sheaths. Moreover, the microarray-based data implied thatthe dominant processes associated with functional leaf sheath transition from sink to source were carbohydrate metabolism and the translocation of the carbon and nitrogen sources and inorganic phosphate.