Abstract
Despite increasing understanding of the importance of the splicing of U12-type introns in plant development, the key question of which U12 intron-containing genes are essential for plant development has not yet been explored. Here, we assessed the functional role of the quatre-quart1 (QQT1) gene, one of the ~230 U12 intron-containing genes in Arabidopsis thaliana. Expression of QQT1 in the U11/U12-31K small nuclear ribonucleoprotein mutant (31k) rescued the developmental-defect phenotypes of the 31k mutant, whereas the miRNA-mediated qqt1 knockdown mutants displayed severe defects in growth and development, including severely arrested stem growth, small size, and the formation of serrated leaves. The structures of the shoot apical meristems in the qqt1 mutants were abnormal and disordered. Identification of QQT1-interacting proteins via a yeast two-hybrid screening and a firefly luciferase complementation-imaging assay revealed that a variety of proteins, including many chloroplast-targeted proteins, interacted with QQT1. Importantly, the levels of chloroplast-targeted proteins in the chloroplast were reduced, and the chloroplast structure was abnormal in the qqt1 mutant. Collectively, these results provide clear evidence that QQT1 is an indispensable U12 intron-containing gene whose correct splicing is crucial for the normal development of Arabidopsis.
Highlights
Splicing of introns in precursor mRNAs is essential for the regulation of gene expression in eukaryotes
Our previous study showed that developmental defects of the 31k mutant plant were caused by improper splicing of many U12 introns (Kim et al, 2010), the key question of which U12 intron-containing genes are essential for plant development has not yet been explored
To determine which U12 intron-containing genes are responsible for the observed developmental-defect phenotypes of the 31k mutant plant, the splicing patterns of the U12 intron genes were comprehensively analyzed in different mutant lines
Summary
Splicing of introns in precursor mRNAs is essential for the regulation of gene expression in eukaryotes. The importance of U12 intron splicing has been demonstrated in the development of animals (Otake et al, 2002; Edery et al, 2011; He et al, 2011; Sikand and Shukla, 2011) and in nonsense-mediated mRNA decay and cell viability (Hirose et al, 2004; Will et al, 2004). During the assembly and function of the minor spliceosome, the U11 and U12 small nuclear ribonucleoproteins (snRNPs) form a U11/U12 di-snRNP complex, and several proteins, including U11/U12-20K, -25K, -31K, -35K, -48K, -59K, and -65K, are uniquely associated with the minor spliceosome in both animals and plants (Schneider et al, 2002; Will et al, 2004). These minor spliceosome-specific proteins are well conserved in both dicot and monocot plants (Schneider et al, 2002; Will et al, 2004; Russell et al, 2006)
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