AUTHOR=Zhao Wenju , Li Xiaojuan , Wen Junqin , Li Quanhui , Bian Shuanling , Ren Yanjing 

TITLE=BrTTG1 regulates seed coat proanthocyanidin formation through a direct interaction with structural gene promoters of flavonoid pathway and glutathione S-transferases in Brassica rapa L.

JOURNAL=Frontiers in Plant Science

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1372477

DOI=10.3389/fpls.2024.1372477

ISSN=1664-462X

ABSTRACT=<sec><title>Introduction</title><p>Seed coat color is a significant agronomic trait in horticultural crops such as <italic>Brassica rapa</italic> which is characterized by brown or yellow seed coat coloration. Previous <italic>Brassica rapa</italic> studies have shown that <italic>BrTTG1</italic> is responsible for seed coat proanthocyanidin formation, which is dependent on the MYB-bHLH-WD40 complex, whereas some studies have reported that TRANSPARENT TESTA GLABRA 1 (TTG1) directly interacts with the structural gene promoters of the flavonoid pathway. </p></sec><sec><title>Methods</title><p>Herein, the brown-seeded inbred B147 and ttg1 yellow-seeded inbred B80 mutants were used as plant materials for gene expression level analysis, gene promoter clone and transient overexpression.</p></sec><sec><title>Results</title><p>The analysis identified eleven structural genes involved in the flavonoid biosynthesis pathway, which are potentially responsible for <italic>BrTTG1</italic>- dependent seed coat proanthocyanidin formation. The promoters of these genes were cloned and cis-acting elements were identified. Yeast one-hybrid and dual-luciferase assays confirmed that BrTTG1 directly and independently interacted with <italic>proCHS-Bra008792, proDFR-Bra027457, proTT12-Bra003361, proTT19-Bra008570, proTT19-Bra023602</italic> and <italic>proAHA10-Bra016610</italic>. A TTG1-binding motif (RTWWGTRGM) was also identified. Overexpression of TTG1 in the yellow-seed <italic>B. rapa</italic> inbred induced proanthocyanidin accumulation by increasing the expression levels of related genes. </p></sec><sec><title>Discussion</title><p>Our study unveiled, for the first time, the direct interaction between TTG1 and the promoters of the flavonoid biosynthesis pathway structural genes and glutathione S-transferases in <italic>Brassica rapa</italic>. Additionally, we have identified a novel TTG1-binding motif, providing a basis for further exploration into the function of TTG1 and the accumulation of proanthocyanidins in seed coats.</p></sec>