Overproduction of OsSLRL2 alters the development of transgenic Arabidopsis plants

SLR1 (SLENDER RICE 1) was thought to be the sole DELLA protein in rice considering the constitutive GA response phenotype of slr1 mutants. There were two other SLR1 homologous SLRL1 and SLRL2 (SLR1 like 1 and 2) which did not have DELLA domain but still shared high level similarity to the C-terminal region of SLR1 found after searching the whole rice genome. SLRL2 specially expressed in the embryo of immature rice seeds and the expression of SLRL2 was increased when treated with GA3. The SLRL2 over-expressed transgenic Arabidopsis plants were semi-dwarfed, late flowering, and insensitive to GA. Moreover, the expression of AtGA20ox1 and AtGA3ox1 was increased and the expression of AtGA2ox1 decreased, indicating SLRL2 was a repressor of GA signaling. We suggested SLRL2 might function to overcome too strong GA responses and maintained a basic repression. Furthermore, a different form of DELLA family in monocots against dicots was discussed.