A 4 bp InDel in the Promoter of Wheat Gene TaAFP-B Affecting Seed Dormancy Confirmed in Transgenic Rice

Wheat (Triticum aestivum L.) ABA insensitive five (ABI5) binding protein gene (TaAFP) is a homologue of the ABI5 binding protein (AFP) gene in Arabidopsis thaliana. It is well documented that AtAFP is a negative regulator of ABA signaling that regulates embryo germination and seed dormancy. TaABI5 was earlier shown to be expressed specifically in seed and its transcript accumulated during wheat grain maturation and acquisition of dormancy. It plays an important role in seed dormancy. In a previous study, we identified two allelic variants TaAFP-B1a and TaAFP-B1b of TaAFP on chromosome arm 2BS in common wheat, designated as, respectively. Sequence analysis revealed a 4 bp insertion in the promoter of TaAFP-B1a compared with TaAFP-B1b that affected mRNA transcription level, mRNA stability, GUS and tdTomatoER translation level, and GUS activity determining seed dormancy.

The transcription and translation levels of TaAFP-B were significantly reduced in TaAFP-Ba and TaAFP-Ba-GFP transgenic plants compared with TaAFP-Bb and TaAFP-Bb-GFP. The average GI (germination index) values of TaAFP-Ba and TaAFP-Ba-GFP were significantly lower than those of TaAFP-Bb and TaAFP-Bb-GFP in T1 and T2 transgenic rice seeds, whereas mature TaAFP-Ba and TaAFP-Ba-GFP transgenic seeds exhibited increased ABA sensitivity and content of endogenous ABA compared with TaAFP-Bb and TaAFP-Bb-GFP.

The 4 bp insertion in the promoter of TaAFP-Ba decreased transcript abundance and translation level in transgenic rice. This insertion increased sensitivity to ABA and content of endogenous ABA in mature seeds, leading to a higher seed dormancy and pre-harvest sprouting tolerance in transgenic rice.