Fig. 6. Effect of overexpressing GeSUT4on Arabidopsis growth.

(a) Transcripts of GeSUT4 in transgenic Arabidopsis. Total mRNA was extracted from leaves of transgenic Arabidopsis overexpressingGeSUT4 (OE-12, 13, 14, 19) or the empty vector (vector). Expression of GeAct7 was used as a loading control. (b) Effect of excess sucrose on root growth of transgenic Arabidopsis. Seedlings were saw and grown on media containing various concentrations of sucrose for 7 d. Primary root lengths were then measured. (c) Leaf areas of transgenic Arabidopsis plants. The whole aerial parts of 4 week-old soil-grown plants were imaged and total leaf areas were analyzed by image J. (d) Colonization ability of Bacillus subtilis on transgenic Arabidopsis roots. Nine-day-old seedlings were incubated with media containing Bacillus suspension. After 4 h, whole roots were collected and CFU were analyzed. Results are mean ± SE (n=8-12 in b, 7 in c, and 6 in d). Significant differences from
seedlings expressing the empty vector were determined.Fig 7. A model for GeSUT4 function in G. elata.When the juvenile tuber of G. elata establishes symbiosis withArmillaria, monosaccharides derived from degradation of fungus cells are quickly transferred to sucrose via plasma-membrane localized sucrose synthase. To prevent carbon loss, the
plasma-membrane Ge SUT4 symporter at the symbiotic interface mediates actively sucrose uptake into symbiotic cortical cells. Sucrose is then needed to be translocated to inner large cells with thick cell wall barriers, where Ge SUT4 also promotes active sucrose uptake to translocated sucrose into the cytosol of large cells for further distribution. Upon demand, tonoplast-localized Ge SUT4 can also actively export stored sucrose for metabolic need.