Isolation and expression of a novel starch-storing cell-specific gene containing the KH RNA binding domain from tobacco-cultured cells BY-2

In cultured Bright Yellow-2 tobacco (Nicotiana tabacum) cells, the depletion of 2,4-dichlorophenoxyacetic acid (2,4-D) in the culture medium induces amyloplast development. This differentiation also includes a decrease in cell multiplication, and an increase in cell size. These changes were primarily triggered by the depletion of 2,4-D, and accelerated by the addition of benzyladenine (BA). Three cDNAs were identified whose transcript levels are specifically increased during differentiation of starch-storing cells using the differential display method, and designated as starch-storing cell induced genes (SCI genes). One of these cDNAs, SCI2 encodes a 285 amino acids long protein with a KH RNA-binding domain. A database search revealed that this protein showed similarity to respective domains of mammalian quaking proteins. 2,4-D addition, which can convert starch-storing cells into dividing cells, to starch-storing BY-2 cells, immediately decreases the SCI2 transcript level, suggesting that SCI2 may have some role in starch-storing cell differentiation in BY-2 cells.