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. 2021 Apr 1;9:651278. doi: 10.3389/fcell.2021.651278

FIGURE 1.

FIGURE 1

Functional analysis of PSTVd secondary structure and pathways for systemic trafficking of PSTVd in an infected plant. (A) PSTVd consists 359 RNA nucleotides folded into a secondary structure, which contains 26 base pair stems and 27 loops. Loop 6, 7, 27 represent different unpaired single circular stranded regions of PSTVd. The nucleosides U43/C318 in PSTVd loop7 played a key role in mediating the transport of PSTVd from bundle sheath to phloem. The six nucleosides of loop 6, G36, A37, C38, C323, G324, and A325, when the mutated nucleosides (G36U/A37C/C38G) close loop 6, its systematic transport was limited, and loop 6 was very important for the transport of PSTVd from palisade mesophyll to spongy mesophyll. The U178G/U179G double mutant in loop27 has replication ability in tobacco cells, but it can only spread in the upper epidermis of inoculated leaves, suggesting that the bases in loop27 will affect the transport of PSTVd from epidermis to palisade mesophyll cells in N. benthamiana. (B) The black arrows illustrate the distinct steps of PSTVd cell-to-cell transport in leaves. Cell types are indicated on the right in B with different colors.