Translational repression of FZP mediated by CU‐rich element/OsPTB interactions modulates panicle development in rice

Abstract

SUMMARY Panicle development is an important determinant of the grain number in rice. A thorough characterization of the molecular mechanism underlying panicle development will lead to improved breeding of high‐yielding rice varieties. Frizzy Panicle (FZP), a critical gene for panicle development, is regulated by OsBZR1 and OsARFs at the transcriptional stage. However, the translational modulation of FZP has not been reported. We reveal that the CU‐rich elements (CUREs) in the 3′ UTR of the FZP mRNA are crucial for efficient FZP translation. The knockout of CUREs in the FZP 3′ UTR or the over‐expression of the FZP 3′ UTR fragment containing CUREs resulted in an increase in FZP mRNA translation efficiency. Moreover, the number of secondary branches (NSB) and the grain number per panicle (GNP) decreased in the transformed rice plants. The CUREs in the 3′ UTR of FZP mRNA were verified as the targets of the polypyrimidine tract‐binding proteins OsPTB1 and OsPTB2 in rice. Both OsPTB1 and OsPTB2 were highly expressed in young panicles. The knockout of OsPTB1/2 resulted in an increase in the FZP translational efficiency and a decrease in the NSB and GNP. Furthermore, the over‐expression of OsPTB1/2 decreased the translation of the reporter gene fused to FZP 3′ UTR in vivo and in vitro. These results suggest that OsPTB1/2 can mediate FZP translational repression by interacting with CUREs in the 3′ UTR of FZP mRNA, leading to changes in the NSB and GNP. Accordingly, in addition to transcriptional regulation, FZP expression is also fine‐tuned at the translational stage during rice panicle development.

African rice (Oryza glaberrima) genomic introgressions impacting upon panicle architecture in Asian rice (O. sativa) lead to the identification of key QTLs

“…An InDel of 9 bp in OgFZP results in the insertion of three histidine amino acids outside the single AP2 domain in the OgFZP protein. Several recent studies have shown that variations in the promoter region and 3' UTR (Untranslated Transcribed Region) of the OsFZP gene affect panicle architecture by through changes in the number of branches produced (Bai et al, 2016(Bai et al, , 2017Huang et al, 2018;Wang et al, 2020;Chen et al, 2022). Here, we observed several SNPs and InDels between the promoter of the two orthologs, which result in a differential presence of TFBSs (Fig.…”

“…5C). Recently, it has been shown that CU-rich elements (CUREs) present in the 3' UTR of the OsFZP mRNA are crucial for efficient OsFZP translational repression (Chen et al, 2022).…”

“…Moreover, recent studies revealed OsFZP as the causal gene of QTLs for grain number per panicle (Bai et al, 2017;Fujishiro et al, 2018;Huang et al, 2018;Wang et al, 2020) and showed that the fine-tuning of OsFZP expression at the transcriptional and post-translational levels could determine panicle architecture (Bai et al, 2017;Huang et al, 2018;Chen et al, 2022). Some SNPs and InDel variations between the Os_Caiapó and Og_MG12 genomes were detected within the promoter region of the two FZP orthologs.…”

“…We also observed a deletion in the CU-rich elements (CUREs) localized in the 3'UTR of OgFZP in comparison to its Og_Caiapó ortholog. This element is known to be crucial for efficient OsFZP translation repression, via the binding with OsPTB1 and OsPTB2 polypyrimidine trans-binding proteins acting as repressors (Chen et al, 2022). Accordingly, these two variations observed in regulatory regions of OgFZP could result in an increase in transcript and/or protein amounts, leading to a precocious transition from branch to spikelet primordium.…”

African rice (Oryza glaberrima) genomic introgressions impacting upon panicle architecture in Asian rice (O. sativa) lead to the identification of key QTLs

“…Reduced expression of OsFZP at the reproductive stage increases the extent of higher order branching of the panicle, resulting in increased grain number (Bai et al, 2016). Moreover, recent studies revealed OsFZP as the causal gene of QTLs for grain number per panicle (Bai et (Bai et al, 2017;Huang et al, 2018;Chen et al, 2022). Some SNPs and InDel variations between the Os_Caiapó and Og_MG12 genomes were detected within the promoter region of the two FZP orthologs.…”