RT Journal
A1 Fu, Yan
A1 Bannach, Oliver
A1 Chen, Hao
A1 Teune, Jan-Hendrik
A1 Schmitz, Axel
A1 Steger, Gerhard
A1 Xiong, Liming
A1 Barbazuk, W. Brad
T1 Alternative splicing of anciently exonized 5S rRNA regulates plant transcription factor TFIIIA
JF Genome Research 
JO Genome Research 
YR 2009 
FD May 01 
VO 19 
IS 5 
SP 913 
OP 921 
DO 10.1101/gr.086876.108 
UL http://genome.cshlp.org/content/19/5/913.abstract 
AB Identifying conserved alternative splicing (AS) events among evolutionarily distant species can prioritize AS events for functional characterization and help uncover relevant cis- and trans-regulatory factors. A genome-wide search for conserved cassette exon AS events in higher plants revealed the exonization of 5S ribosomal RNA (5S rRNA) within the gene of its own transcription regulator, TFIIIA (transcription factor for polymerase III A). The 5S rRNA-derived exon in TFIIIA gene exists in all representative land plant species but not in green algae and nonplant species, suggesting it is specific to land plants. TFIIIA is essential for RNA polymerase III-based transcription of 5S rRNA in eukaryotes. Integrating comparative genomics and molecular biology revealed that the conserved cassette exon derived from 5S rRNA is coupled with nonsense-mediated mRNA decay. Utilizing multiple independent Arabidopsis overexpressing TFIIIA transgenic lines under osmotic and salt stress, strong accordance between phenotypic and molecular evidence reveals the biological relevance of AS of the exonized 5S rRNA in quantitative autoregulation of TFIIIA homeostasis. Most significantly, this study provides the first evidence of ancient exaptation of 5S rRNA in plants, suggesting a novel gene regulation model mediated by the AS of an anciently exonized noncoding element.