Figures (4)  Tables (1)
    • Figure 1. 

      Model diagram of tomato epidermal trichomes. In tomato, epidermal trichomes that protrude outward from the epidermal cells usually develop into three common types: long glandular trichomes (Type I, IV), short glandular trichomes (Type VI, VII), and long non-glandular trichomes (Type II, III, V).

    • Figure 2. 

      Epidermal trichomes of eight types of cucumber. Bar = 500 μm (II–IV); 100 μm (V); 20 μm (VI); or 5 μm (I, VII, and VIII). This image is quoted from Xue et al.[29]

    • Figure 3. 

      A model for regulating different types of trichome development in tomato. Different types of tomato trichomes are presented in the green box. The colored lines correspond to different phytohormones-related regulatory pathways. The transcription factors Wo, H, Ln and CycB2 play an essential role in trichome development.

    • Figure 4. 

      A proposed cucumber trichome regulatory scheme. Tril/CsGL3, TBH/CsGL1/MICT are key transcription factors regulating trichomes in cucumber. In particular, the transcription factors in the blue circles represent different alleles of a gene, in which Mict can interact with TTG1 to regulate the initiation of trichomes[32]. CsSBS1 can form a trimeric complex with CsTTG1 and CsGL1, thereby regulating trichome formation, and the gene CsGL1 has an epistatic effect on CsSBS1[65]. In addition, these transcription factors affect trichome development by regulating the expression of downstream genes or modulating phytohormone signaling pathways.

    • TypesTFsSpeciesFunctionEffectMetabolite productionHormone involvedReference
      bHLHSlMYC1TomatoType VI formationPTerpenoids[39]
      CsbHLH1CucumberGlandular trichome formationP[21]
      HECATE2CucumberTrichome densityPCTK[64]
      bHLH95TomatoTrichome initiationNGA[48]
      MYBSlMX1TomatoGlandular trichome densityP; NTerpenoids, carotenoids, and phenylpropanoids[40,69]
      SlMixta-likeTomatoTrichome InitiationN[41]
      CsTRYCucumberTrichome densityN[32,61]
      CsMYB6CucumberTrichome initiationN[60,61]
      MYB52TomatoTypes V formationNAUX[49]
      SlTHM1TomatoTypes II, V and VI formationNAUX/JA[46,49]
      MYB75TomatoTypes II, V and VI formationNSesquiterpeneAUX[49,50]
      HD-ZIPWollyTomatoType I densityPTerpenoidsJA, AUX and GA[36,70]
      SlHZ45TomatoTrichome density (especially Type I,IV,VI)P[71]
      HDZIV8Tomatotrichome morphologyP[72]
      LnTomatoTrichome density[19]
      CsGL3/TrilCucumberTrichome initiationP[53,54,73]
      Tbh/Mict/CsGL1CucumberTrichome morphogenesisP; NFlavonoids[56,57,62,74,75]
      CsGL2CucumberTrichome densityP[71,76]
      SlCD2TomatoTrichome formation (especially Type VI)P[70]
      SlHD8TomatoTrichomes elongationP[47]
      CsSBS1CucumberTrichome developmentPETH[65]
      Mict-L130FCucumberTrichome morphogenesisN[77]
      HairinessPepperType II, III, V formationP[33]
      ZFPsCsTuCucumberTrichome formationP[63,73]
      Hair/Hair-like (HL)/ SPARSE Hair (SH)TomatoType I formationPJA[38,46,78]
      SlZFP8 LikeTomatoTrichomes initiation and elongationP[20]
      ZFP6TomatoTrichomes density and lengthP[20]
      WD-repeat proteinCsTTG1CucumberTrichome densityP[32]
      CyclinSlCycB2TomatoTrichome densityP[36,37]
      SlCycB3TomatoTrichome formationP[19,36,37]
      WAVE regulatory complexHairless (Hl)TomatoTrichome morphologyNSesquiterpenes, flavonoids[79]
      Hairless-2 (Hl-2)TomatoTrichome morphologyN[72]
      ARPC1/Hairless-3 (Hl-3)TomatoTrichome morphology; Trichome density (especially Type I, IV)NTerpenoids[80]
      CHICHI1TomatoTrichomes densityNFlavonoids[5]
      AUX/IAASlIAA15TomatoType I, VI densityPauxin[51]
      ARFSlARF3TomatoType I, VI densityPauxin[51]
      SlARF4TomatoType II, V, VI formationP[49]
      JA relatedJAI-1TomatoType I, VI formationNJA[52]
      JAZ2TomatoTrichome densityNJA[44,46]
      JAZ4TomatoTrichome developmentNJA[47]
      P1Soybeanglabrous[81]
      PsSoybeansparse pubescenceN[81]
      Pd1Soybeandense pubescencePGA, CTK[81]
      Note: P: Positive; N: Negative.

      Table 1. 

      Genes involved in the development of trichomes in tomato, cucumber, pepper and soybean. Table adapted from Feng et al. [35]