3赤霉素 Gibberellins

赤霉素（gibberellins，GAs）是一类非常重要的植物激素，参与许多植物生长发育等多个生物学过程。赤霉素用A₁（GA₁）到A126（GA126）的方式命名，数字依照发现的先后顺序。

赤霉素 Gibberellins

• Discovery of Gibberellins
  • Gibberellins were identified as fungal compounds that promote stem elongation
  • Later, GAs were identified as endogenous plant growth regulators
  • The manipulation of GA levels is tremendously important for agriculture
    • One of the most significant accomplishments of 20th century science was the development of semi-dwarf grain varieties which are deficient in GA synthesis or response
• Types and Structure of Gibberellins
  • Backbone of GAs
• Biosynthesis of Gibberellins
  • The GA biosynthetic pathway is complex
    • Stage 1 proplastid
      • Core Enzyme
        • CPS
          • 柯巴焦磷酸合成酶
        • KS
          • 内根-贝壳杉烯合酶
    • Stage 2 endoemembranes
      • Core enzyme
        • KO
        • KAO
    • Stage 3-Cytoplasma
      • Core enzyme
        • GA 13-hydroxylase
        • GA 20-oxidase
        • GA 3-oxidase
• Metabolism of GAs
  • GAs can be deactivated by several different enzymes
    • GA2ox
    • GAMT
    • EUI
  • Tightly controlled
• Transport of GAs
  • GA is not transported in a polar way
    • The same amount of GA moves from the upper donor block to the lower block no matter the polarity of the stem segment.
    • GAs are graft-transmissible; they can move long distances
    • GA moves from embryo to aleurone in germinating monocot seeds
  • GA moves from embryo to aleurone in germinating monocot seeds
    • GA is synthesized in the embryo and moves into the cells of the aleurone to induce production of α-amylase, an enzyme that breaks down starch
• Perception and signaling
  • GID1
    • GIBBERELLIN INSENSITIVE DWARF1 (GID1) encodes a GA receptor
      • Overexpression of GID1 makes plants hypersensitive to GA
    • GA-INSENSITIVE1 and SLENDER1 both encode “DELLA” repressors
    • The receptor GID1 binds to DELLAs
    • The interaction between GID1 (receptor) and SLR1 (DELLA) is GA-dependent
      • GA induces DELLA protein degradation
  • GID2
    • SLEEPY/GID2 is a component of the SCF ubiquitin ligase complex SCFSLY1/GID2
• Physiological Function
  • GAs control growth and elongation by cell expansion and cell division
    • GAs induce expression of cellcycle regulatory proteins called cyclins
    • GAs promote elongation by cell wall loosening and stabilizing the orientation of cortical microtubules, which help direct growth
  • GAs mediate stress responses through DELLA proteins
  • GAs promote seed germination and reserve mobilization
    • During germination, GA induces expression of nutrient-mobilizing enzymes
  • GAs promote flowering
  • GAs interact with brassinosteroids at transcriptional level