Coordination between GROWTH-REGULATING FACTOR1 and GRF-INTERACTING FACTOR1 plays a key role in regulating leaf growth in rice

BACKGROUND: The interactions between Growth-regulating factors (GRFs) and GRF-Interacting Factors (GIFs) have been well demonstrated but it remains unclear whether different combinations of GRF and GIF play distinctive roles in the pathway downstream of the complex. RESULTS: Here we showed that OsGRF1 and OsGIF1 synergistically regulate leaf growth in rice. The expression of OsGIF1 emerged in all tissues with much higher level while that of OsGRF1 appeared preferentially only in the stem tips containing shoot apical meristem (SAM) and younger leaves containing leaf primordium. Overexpression of an OsmiR396-resistant version of mOsGRF1 resulted in expanded leaves due to increased cell proliferation while knockdown of OsGRF1 displayed an opposite phenotype. Overexpression of OsGIF1 did not exhibit new phenotype while knockdown lines displayed pleiotropic growth defects including shrunken leaves. The crossed lines of mOsGRF1 overexpression and OsGIF1 knockdown still exhibited shrunk leaves, indicating that OsGIF1 is indispensable in leaf growth regulated by OsGRF1. The expression of OsGRF1 could be upregulated by gibberellins (GAs) and downregulated by various stresses while that of OsGIF1 could not. CONCLUSION: Our results suggest that OsGIF1 is in an excessive expression in various tissues and play roles in various aspects of growth while OsGRF1 may specifically involve in leaf growth through titrating OsGIF1. Both internal and external conditions impacting leaf growth are likely via way of regulating the expression of OsGRF1.