Model of GhRCD1-GhMYC3 module synergistically regulating cotton seed development and fiber elongation (IMAGE)
Caption
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.
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