AUTHOR=Nasim Zeeshan , Fahim Muhammad , Ahn Ji Hoon 

TITLE=Possible Role of MADS AFFECTING FLOWERING 3 and B-BOX DOMAIN PROTEIN 19 in Flowering Time Regulation of Arabidopsis Mutants with Defects in Nonsense-Mediated mRNA Decay

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.00191

DOI=10.3389/fpls.2017.00191

ISSN=1664-462X

ABSTRACT=<p>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 <italic>UPF1</italic> and <italic>UPF3</italic> leads to various developmental defects, little is known about the mechanism underlying the regulation of flowering time by NMD. Here, we showed that the <italic>upf1-5</italic> and <italic>upf3-1</italic> mutants had a late-flowering phenotype under long-day conditions and the <italic>upf1-5 upf3-1</italic> double mutants had an additive effect in delaying flowering time. RNA sequencing of the <italic>upf</italic> mutants revealed that <italic>UPF3</italic> exerted a stronger effect than <italic>UPF1</italic> in the <italic>UPF</italic>-mediated regulation of flowering time. Among genes known to regulate flowering time, <italic>FLOWERING LOCUS C</italic> (<italic>FLC</italic>) mRNA levels increased (up to 8-fold) in <italic>upf</italic> mutants, as confirmed by qPCR. The <italic>upf1-5, upf3-1</italic>, and <italic>upf1-5 upf3-1</italic> mutants responded to vernalization, suggesting a role of <italic>FLC</italic> in delayed flowering of <italic>upf</italic> mutants. Consistent with the high <italic>FLC</italic> transcript levels and delayed flowering in <italic>upf</italic> mutants, levels of <italic>FLOWERING LOCUS T</italic> (<italic>FT</italic>) and <italic>SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1</italic> (<italic>SOC1</italic>) mRNAs were reduced in the <italic>upf</italic> mutants. However, RNA-seq did not identify an aberrant <italic>FLC</italic> transcript containing a premature termination codon (PTC), suggesting that <italic>FLC</italic> is not a direct target in the regulation of flowering time by NMD. Among flowering time regulators that act in an <italic>FLC</italic>-dependent manner, we found that <italic>MAF3, NF-YA2, NF-YA5</italic>, and <italic>TAF14</italic> showed increased transcript levels in <italic>upf</italic> mutants. We also found that <italic>BBX19</italic> and <italic>ATC</italic>, which act in an <italic>FLC</italic>-independent manner, showed increased transcript levels in <italic>upf</italic> mutants. An aberrant transcript containing a PTC was identified from <italic>MAF3</italic> and <italic>BBX19</italic> and the levels of the aberrant transcripts increased in <italic>upf</italic> mutants. Taking these results together, we propose that the late-flowering phenotype of <italic>upf</italic> mutants is mediated by at least two different pathways, namely, by <italic>MAF3</italic> in an <italic>FLC</italic>-dependent manner and by <italic>BBX19</italic> in an <italic>FLC</italic>-independent manner.</p>