Possible Role of and in Flowering Time Regulation of Arabidopsis Mutants with Defects in Nonsense-Mediated mRNA Decay.

Eukaryotic cells use nonsense-mediated mRNA decay (NMD) to clear aberrant mRNAs from the cell, thus preventing the accumulation of truncated proteins. In Arabidopsis, two UP-Frameshift (UPF) proteins, UPF1 and UPF3, play a critical role in NMD. Although deficiency of and leads to various developmental defects, little is known about the mechanism underlying the regulation of flowering time by NMD. Here, we showed that the and mutants had a late-flowering phenotype under long-day conditions and the double mutants had an additive effect in delaying flowering time. RNA sequencing of the mutants revealed that exerted a stronger effect than in the -mediated regulation of flowering time. Among genes known to regulate flowering time, () mRNA levels increased (up to 8-fold) in mutants, as confirmed by qPCR. The , and mutants responded to vernalization, suggesting a role of in delayed flowering of mutants. Consistent with the high transcript levels and delayed flowering in mutants, levels of () and () mRNAs were reduced in the mutants. However, RNA-seq did not identify an aberrant transcript containing a premature termination codon (PTC), suggesting that is not a direct target in the regulation of flowering time by NMD. Among flowering time regulators that act in an -dependent manner, we found that , and showed increased transcript levels in mutants. We also found that and , which act in an -independent manner, showed increased transcript levels in mutants. An aberrant transcript containing a PTC was identified from and and the levels of the aberrant transcripts increased in mutants. Taking these results together, we propose that the late-flowering phenotype of mutants is mediated by at least two different pathways, namely, by in an -dependent manner and by in an -independent manner.