ANALYSIS OF THE LONG-DISTANCE SIGNAL TRANSPORT IN RICE SIEVE TUBES

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Sieve tubes function in the transport of photoassimilates and are also thought to convey certain signals from source to sink. It has been reported that plant hormones and the signal for floral induction are transported via sieve tubes.While these signal-transport systems have been assigned to the sieve tube, it is also possible that other types of signal-transport system might exist in the sieve tube. The nature of the sieve tubes, which is not connected via plasmodesmata to other cells apart from the companion cells, suggests that exogenous signals might be transduced via the cell membrane of the sieve element-companion cell complex. Such signals would be transpoted to the cell, change the level of free Ca^<2+>ions, which can act as a second messenger, and trigger certain events in the cell via the subsequent phosphorylation of proteins in the sieve tube.We already suggested that the Ca-dependent-protein kinases (CDPK) were present in the phloem sap of rice plans by the physiological experiments using a pure phloem sap from rice plants. In this project, we try to clone the gene which encode the CDPK in the leaf of rice plants. By PCR cloning and cDNA libraly screening, we cloned the gene which encode CDPK and CRK (CDPK-related kinase) which is express in rice leaf blade.Now we are making the transgenic rice plant using these kinases and phloem specific promoter which already cloned by our group.