Regulatory mechanism of EL1 for floral repression and spikelet development in rice

Abstract

Genetic factor strongly influence flowering time and reproductive organ development, which are the key factors affecting grain production in rice and other crops. Multiple pathways determine flowering time through transcriptional and posttranslational regulation. The rice flowering-time repressors Heading date 2 (Hd2), Heading date 6 (Hd6), and Early flowering1 (EL1) encode Oryza sativa Pseudo-Response Regulator 37 (OsPRR37), Casein kinase 2α (CK2α), and Casein kinase I (CKI), respectively, and Hd6 and EL1 genetically act upstream of Hd2 in the floral induction pathway. Protein interaction and phosphorylation assays were performed to show that the protein kinases Hd6/CK2α and EL1/CKI directly phosphorylate Hd2/OsPRR37. Thus, it suggests that the posttranslational modification of OsPRR37 by Hd6/CK2α and EL1/CKI contributes to the regulation of the OsPRR37 activity, which delays flowering time under non-inductive long days. EL1 also controls gibberellin (GA) signaling negatively, as well as a long day-specific repressor of floral induction in rice. The plants harboring non-functional el1 showed that abnormal shape of anther and reduced pollen viability, besides, they displayed the significantly excessive GA response. In addition, the main regulator in GA signaling, GAMYB, and its downstream genes related to pollen development, were uncontrollably upregulated in the spikelets at heading stage in the plants harboring non-functional el1 allele. The analyses of yield components indicated that the rice carrying non-functional el1 was reduced their total grain production, especially seed setting rate, compared to wild-types. It implies that EL1 contributes to affect reproductive organ development and grain productivity in rice through controlling GA signal transduction.