Two splice variants of the IDD14 transcription factor competitively form nonfunctional heterodimers which may regulate starch metabolism

Alternative splicing of primary gene transcripts provides eukaryotic cells, with a critical scheme for enriching transcriptome and proteome diversity. Here we report that alternative splicing of the Arabidopsis INDERMINATE DOMAIN 14 (IDD14) transcription factor gene generates a competitive inhibitor in regulating starch metabolism. An alternatively spliced IDD14 form (IDD14 beta), which is produced predominantly under cold conditions, lacks functional DNA-binding domain but is able to form heterodimers with the functional IDD14 form (IDD14 alpha). IDD14 alpha-IDD14 beta heterodimers have reduced binding activity to the promoter of Qua-Quine Starch (QQS) gene that regulates starch accumulation. Transgenic Arabidopsis plants overproducing IDD14 alpha (35S:IDD14 alpha) exhibited retarded growth with pale green leaves as appeared on QQS-overexpressing plants. Notably, IDD14 beta overproduction rescued the 35S:IDD14 alpha phenotypes. We propose that alternative splicing of the IDD14 gene generates a self-controlled regulatory loop that may modulate starch accumulation in response to cold.