Tannin1 in sorghum does not act as a pleiotropic master regulator of leaf pigmentation or chilling tolerance, supporting a model of subfunctionalization of MBW components in panicoid grasses.
Master regulators are key transcriptional control genes that orchestrate complex regulatory networks, often influencing multiple phenotypes. In crops, these regulators, such as OsWRKY71, CBFs, and SELF-PRUNING, are critical targets for breeding due to their roles in stress response and development. However, their pleiotropic nature can lead to undesired tradeoffs. In Sorghum bicolor, the MBW complex—including Tannin1 (WDR), Tannin2 (bHLH), and Y1 (MYB)—regulates traits such as grain pigmentation and possibly chilling tolerance. Tannin1, in particular, colocalizes with chilling tolerance QTL qCT04.62, suggesting a potential pleiotropic role. Researchers from Colorado State University tested two hypotheses regarding Tannin1: one proposing conserved ancestral pleiotropy across panicoid grasses, and the other proposing a derived loss of pleiotropic function. Using transcriptomic comparisons of near-isogenic lines (NILs) with wild-type and loss-of-function Tan1 alleles, researchers found minimal trans-regulatory effects, indicating Tannin1 does not regulate leaf pigmentation or chilling tolerance in sorghum.
These findings support the derived loss of pleiotropy hypothesis and suggest that MBW regulatory roles in sorghum have undergone subfunctionalization. While Arabidopsis TTG1 and rice OsTTG1 retain broad pleiotropic roles, Tannin1 in sorghum appears restricted to proanthocyanidin regulation in seeds. The existence of at least 12 WDR paralogs in sorghum and their diverse expression patterns point toward partitioned functions across distinct flavonoid systems. This evolutionary divergence implies that sorghum, and possibly other panicoid grasses like maize and Setaria, have adapted MBW complex roles through gene duplication and regulatory specialization. These insights reshape the classical view of MBW master regulation and offer new avenues for trait-specific molecular breeding in cereals.
SorghumBase examples:
Reference:
Schuh A, Morris GP. Loss of Pleiotropic Regulatory Functions in Tannin1, the Sorghum Ortholog of Arabidopsis Master Regulator TTG1. Plant Direct. 2025 Mar 12;9(3):e70055. PMID: 40084038. doi: 10.1002/pld3.70055. Read more
Related Project Websites:
- Morris Lab at Colorado State University: https://www.morrislab.org/