Alternative splicing of activator CcbHLH1 gene accounts for anthocyanin absence in white cornflower

Le résumé fourni par la source

Anthocyanins play crucial roles in conferring multicolored characteristics to higher plant organs. Previous studies have investigated the absence of anthocyanin accumulation in white cornflower petals, where the anthocyanin biosynthesis pathway was obstructed by CcF3H. However, the genetic regulation mechanism underlying anthocyanin absence remained unclear. In the present study, the full-length sequences of two transcription activators CcMYB6-1 and CcbHLH1 were isolated in white cornflower petals. The multi-sequence alignment analysis revealed that there was no difference in the CcMYB6-1 sequence between the blue and white petals, while CcbHLH1 was truncated to a length of 1,125 bp on account of alternative splicing, resulting in a frame-shift mutation and premature codon, leading to the loss of basic, helix-loop-helix domains. The truncated CcbHLH1 could still interact with CcMYB6-1 as demonstrated by yeast-two hybrid and bimolecular luminescence complementary assays but lost the ability to enhance the trans-activation of CcDFR promoter using dual-luciferase assay. Transient over-expression of mutated CcbHLH1 in tobacco leaves resulted in a significant decrease in anthocyanin production. These results suggested the alternative splicing of CcbHLH1 caused the incapacity of trans-activating the anthocyanin biosynthetic pathway together with CcMYB6-1, finally leading to anthocyanin absence in white cornflower. The present findings further shed light on the genetic regulation mechanism of anthocyanin biosynthesis in cornflower and enrich the knowledge underlying the white color transition in higher plants.

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