Harmon, F. G. | Search bioRxiv

bioRxiv2023

Lariat debranching by RNA DEBRANCHING ENZYME 1 depends on SICKLE in Arabidopsis thaliana

Spliceosome mediated intron removal from precursor mRNAs (pre-mRNAs) generates circular RNAs called intron lariats. RNA DEBRANCHING ENZYME 1 (DBR1) ribonucleases linearize, or debranch, intron lariats to allow their degradation. DBR1 genes occur across eukaryotes and are essential in animals and plants. High levels of intron lariats in the weak Arabidopsis thaliana dbr1-2 allele inhibits primary microRNA (pri-miRNA) processing, disrupting miRNA production and miRNA-regulated growth and development. Arabidopsis sickle (sic) mutants alter pri-miRNA processing and pre-mRNA splicing. This study demonstrates sic mutants accumulate intron lariats matching those in weak dbr alleles. The strong sic-1 and weak dbr1-3 alleles together cause synthetic lethality, while weak sic-3 with dbr1-3 has intron lariat accumulation like sic-3. Further, sic-3, dbr1-3, and sic-3 dbr1-3 similarly alter circadian rhythms and growth of roots and rosettes. The conserved MPLKIP amino acid motif in SIC mediates physical interaction with DBR1 in vitro and is required for intron lariat debranching in vivo. Thus, MPLKIP containing proteins, like SIC and human TTDN1, act with cognate DBR1 proteins to maintain RNA homeostasis critical for growth and development.

molecular biology↗

bioRxiv2018

GIGANTEA promotes sorghum flowering by stimulating floral activator gene expression

iv. FundingThis work was supported by USDA-ARS CRIS projects 2030-21000-039-00D and 2030-21000-049-00D to F.G.H.\n\nv. AbstractThe C4 grass Sorghum bicolor is an important grain and subsistence crop, animal forage, and cellulosic biofuel feedstock that is tolerant of abiotic stresses and marginal soils. Sorghum is short-day flowering, an obstacle for adaptation as a grain crop but a benefit as a biofuel feedstock. To identify genes underlying sorghum photoperiodic flowering behavior this study characterized the Sbgi-ems1 nonsense mutation in the sorghum GIGANTEA (SbGI) gene from a sequenced M4 EMS-mutagenized BTx623 population. Sbgi-ems1 plants had reduced stature and leaf blades exhibiting increased lateral growth combined with reduced proximal-distal growth. Mutant plants flowered later than normal siblings under long-day conditions provided by greenhouse or field. Delayed flowering in Sbgi-ems1 plants accompanied by an increase in internode number, indicating an extended vegetative growth phase prior to flowering. Sbgi-ems1 plants had reduced expression of floral activator genes SbCO and SbEhd1 and downstream FT-like florigen genes SbFT, SbCN8, and SbCN12. Therefore, SbGI accelerates flowering by promotion of SbCO and SbEhd1 expression. Circadian clock-associated genes SbTOC1 and SbLHY had disrupted expression in Sbgi-ems1 plants. This work demonstrates SbGI is a key upstream activator in the regulatory networks dictating sorghum flowering time and growth, as well as gene expression regulation within the circadian clock.\n\nSummary StatementSorghum GIGANTEA contributes to flowering time, growth, and the circadian clock with activities opposite to its maize homolog. GI occupies a conserved position within regulatory networks but has plastic activity.

plant biology↗