*2.7. OsbHLH079 Might Directly Regulate the Cell Expansion-Associated Genes*

*PHYTOCHROME INTERACTING FACTOR LIKE1* (*OsPIL1*) functions as a key regulator of internode elongation [77]. *OsPIL1*-overexpressing rice plants (*Ubi::OsPIL1*) formed elongated internodes via larger cells through direct regulation of its downstream genes, such as *OsEXPA4* and *1-ACC OXIDASE*, via binding to the G-box element. Both OsPIL1 and OsbHLH079 are bHLH-type transcription factors. Thus, it can be speculated that OsbHLH079 directly binds to the promoter regions of cell expansion-related genes, such as *OsEXPAs* and *OsXTHs*. The expression of cell expansion-related genes was increased to a much greater extent in the *osbhlh079-D* mutant compared to the increased expression of BR signaling-associated genes (*OsBZR1*, and *ILI1*) (Figure 5c, Figure 7b). The increased expression of BR-related genes in *osbhlh079-D* and *OsbHLH079*-overexpressing plants may have caused a significant change in the expression of the downstream genes, but we could not exclude the possibility that OsbHLH079 directly regulates the cell expansion-associated genes.
