*3.4. A Proposed Modelsummarizing of Spot Formation Pattern in Phalaenopsis 'Panda'*

Our research confirmed *Pe4CL2*, *PeF3H*, *PeF3 H*, and *PeANS* expression were low or repressed in non-spot areas in 'Panda' sepals, and MIR156g and MIR858 may silence the expression of *PeMYB11* and *PeMYB7* in non-spots parts. In conclusion, we illustrated a proposed molecular mechanism in spots formation in 'Panda' (Figure 9). The diagram revealed the unique spot formation in 'panda' may result from the higher expression of MIR156g and MIR858 clusters in non-spot tissue, which targeted and suppressed the expression of key regulate genes *PeMYB7, PeMYB11* and then caused very low expression of *Pe4CL2*, *PeF3H*, *PeF3 H*, and *PeANS* in non-spot tissue. These results finally led to the lack of synthesis and accumulation of anthocyanin in non-spot area.

**Figure 9.** A proposed model summarizing of spot formation pattern in *Phalaenopsis* 'Panda' sepal. The purple segment illustrates the accumulation of anthocyanidin in spot area of 'Panda'. MIR156g, MIR858 target on key regulate genes *PeMYB7* and *PeMYB11*, suppressed the transcript level of *Pe4CL2*, *PeF3H*, *PeF3 H*, *PeANS* and resulted in reduced anthocyanidin production in the non-spot area, while relatively lower expression levels of MIR156g and MIR858 and high levels of transcription of these genes in spot area cause accumulation of anthocyanidin. The black dashed arrows represent low levels of transcription, while the black solid-line arrows represent high levels of transcription. The yellow solid-line arrows represent promoting transcription, while yellow dashed arrow represent lack of promotion function. The blue bold solid-line T-arrow represents interfering transcription, while blue bold dashed arrow represents lack of interference function. The red bold arrow represents upregulation, and the green bold arrow represents downregulation. DHK, dihydrokaempferol; DHQ, dihydroquercetin; DHM, dihydromyricetin; LC, leucocyanidin; LD, leucodelphinidin; Cy, cyanidin; De, delphinidin.
