image: GhRCD1 and GhMYC3 display mutually opposite expression patterns during the synchronized development of cotton fibers and seeds. In the early developmental window (0‑20 DPA, fiber‑elongation phase), GhRCD1 accumulates at high levels in fibers and forms heterodimers with GhMYC3. This interaction blocks GhMYC3 from repressing peroxidase‑encoding (*PER*) genes. Higher peroxidase (POD) activity lowers reactive‑oxygen‑species (ROS) levels and boosts pectin methylesterase (PME) activity. Low‑methyl‑esterified pectin forms calcium‑dependent “egg‑box” structures that stiffen the seed coat and restrain seed germination. Meanwhile, the GhRCD1‑GhMYC3 complex relieves GhMYC3‑driven repression of fatty‑acid biosynthetic genes (*GhKCS12*, *GhCUT1*, *GhFAD7A‑1*). Elevated production of very‑long‑chain fatty acids drives robust fiber elongation. During seed‑vigor establishment (20‑35 DPA), GhRCD1 expression declines. Freed GhMYC3 binds and suppresses *PER* promoters, reducing POD activity and triggering ROS buildup. Elevated ROS represses PME activity, generating highly methyl‑esterified pectin that disrupts egg‑box cross‑links. Seed coats soften, improving seed vigor. Excess ROS directly suppresses further fiber growth. GhMYC3 also curtails fiber elongation by repressing key fatty‑acid biosynthetic genes and limiting very‑long‑chain fatty‑acid production.
Credit: ©Science China Press
Cotton provides the world’s major natural textile fiber, while cotton seeds serve as propagation material and oil resource feedstock. However, a long standing biological bottleneck constrains cotton improvement: fiber elongation and seed oil and vigor are mutually constrained. Improving one trait frequently sacrifices performance of the other, making it difficult to breed elite cultivars with both high quality fiber and cotton seed.
Fibers and seeds develop synchronously from cotton ovules, yet the underlying molecular mechanism behind this trade off remained unclear. A joint research team from Zhengzhou University, the Institute of Cotton Research (CAAS), National Nanfan Research Institute and other institutions has uncovered a key antagonistic regulatory module, GhRCD1- GhMYC3.
GhRCD1 promotes fiber elongation yet suppresses seed vigor, whereas transcription factor GhMYC3 exerts opposite biological effects. Using CRISPR Cas9 editing, RNA interference, and biochemical assays, the team confirmed that GhRCD1 physically binds GhMYC3 via its RST protein domain. This protein protein interaction weakens GhMYC3’s capacity to repress downstream target genes.
During fiber elongation stage (0- 20 days post anthesis, DPA), high GhRCD1 abundance sequesters GhMYC3. This releases repression of peroxidase genes and fatty acid biosynthetic genes, balancing ROS levels and boosting linolenic acid and very long chain fatty acid accumulation to drive fiber cell growth. When seeds enter oil and vigor establishment phase (after 20 DPA), GhRCD1 expression drops. Freed GhMYC3 binds to promoters of peroxidase and fatty acid synthesis genes, reshaping ROS signaling and cell wall mechanical properties to build strong seed vigor and oil accumulaltion, while slowing fiber elongation.
Notably, reactive oxygen species (ROS) function in a dose dependent manner: moderate ROS benefits fiber cell expansion and seed germination, but excess ROS triggers oxidative damage. The GhRCD1 GhMYC3 module acts as a fine tuning rheostat, adjusting ROS concentration and pectin methylesterification to modify seed coat hardness, alongside redistributing fatty acid resources between fibers and seeds.
“This work reveals how cotton balances limited biological resources for two key organs,” explained Dr. Zhi Wang, corresponding author. “Rather than a simple on-off switch, this module responds to developmental timing. We can take advantage of the spatial and temporal separation of fiber growth and seed maturation stages for precision breeding.”
For practical breeding applications, tissue specific genetic modification is proposed. Fiber specific overexpression of GhRCD1 may boost fiber length without impairing seed quality; seed stage specific manipulation of GhMYC3 can enhance seed vigor without penalty for fiber traits. This strategy opens routes to break the natural trade off, generating new cotton germplasm with superior fiber and high vigour seed performance for field planting.
The authors note that further multi omics and field trials are still required to translate these laboratory discoveries into commercial cotton varieties.
Quote from Fuguang Li, corresponding author: “Cotton is a strategic crop for China. Decoding this trade-off mechanism fills a critical gap in cotton developmental biology and supports molecular design breeding for sustainable cotton production.”
About the institutions:
Zhengzhou Research Base, State Key Laboratory of Cotton Bio breeding and Integrated Utilization; Institute of Cotton Research, Chinese Academy of Agricultural Sciences carries out fundamental and applied research on cotton genetics, germplasm innovation and molecular breeding.
Journal
Science China Life Sciences
Method of Research
Experimental study