Abstract
GIGANTEA (GI) has been considered to be involved in circadian clock pathway to regulate the flowering in plants. Mutation in GI delays the flowering time and increases the tolerance to oxidative stress in the Arabidopsis thaliana. To further investigate the multiple functions for GI, GI orthologues (PcGI and AcGI) were cloned from non-flowering ferns Adiantum capillus-veneris L. and Pteris cretica cv. Albolineata. The expression of fern’s GIs also showed a circadian rhythm with the highest expression at 8 to 12 h of the light period and the lowest expression at dawn. A partial rescue of late flowering phenotype by activating CONSTANS (CO), FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS (SOC1) was observed in the gi mutant of Arabidopsis ectopically expressed fern’s GIs. This implied the function of GI genes is conserved in flowering and non-flowering plants. Ectopic expression of PcAt-GI which contains the N-terminal of PcGI and C-terminal of AtGI could rescue the late-flowering of gi mutants stronger than AtPc-GI which contains the N-terminal of AtGI and C-terminal of PcGI. Furthermore, ectopic expression of C-terminal portion of GI, PcGI or AcGI promotes flowering in the Arabidopsis gi-1 and gi-2 mutants. By contrast, the N-terminal portion of these three GI orthologues could only weakly promote flowering in gi-1 and gi-2 mutants. These results revealed that the C-terminus of the GI protein is functionally more important in flowering than the N-terminus. Besides flowering time, additional male sterility of the flower due to anther indehiscence was only observed in 35S::AtGI and 35S::AtPc-GI plants. Futher analysis indicated that secondary thickening was absent in the endothecium of anther in 35S::AtGI and 35S::AtPc-GI transgenic Arabidopsis due to the down-regulation of NST1, NST2 and MYB85. Our result implied that the N-terminus of the AtGI contained the function in regulating the anther development once ectopic expressing in Arabidopsis.
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