In this study, we report initial results on the presence and short distance movement of intermediary replication viral strands, i.e., negative genomic strands, in a host resistant maize line (RL1), as well as in a nonhost (sugarcane) for the SCMV-VER1 isolate. Reports of SCMV local movement in resistant germplasms have previously been reported [19, 20] by either monitoring the presence of the CP or immunofluorescent staining of the viral infection.
Virus movement in plants is thought occur through cell-to-cell and systemic movement through the phloem , mainly as RNA-movement protein complexes . For potyviruses, CP protein is considered as an important factor in short and long distance movement , similar to TMV. It has been shown that some TMV mutants are repressed in systemic movement, but not for local spread . This observation indicates that the phloem import mechanism is different of cell-to-cell movement in potyvirus. We present evidence of the presence of SCMV virions in maize stems. This suggests that SCMV is capable of long distance spread in monocot maize SL plants as virions, as previously showed for other viruses (e.g., the Cucumber mosaic virus) using electron microscopy in sieve elements of Nicotiana plants .
Our results also show that the SCMV-VER1 isolate is able to go through the initial steps of replication in host resistant maize (RL) and nonhost sugarcane (SC), and can be detected in its replicative form at 5 dpi (Figure 3). This suggests the existence of uncoated viral RNAs in the replication complexes. Considerably shorter times for uncoating (e.g, 45 seconds) have been suggested for other non potyvirus examples, such as the Turnip yellow mosaic virus (TYMV), a Tymovirus, , or hours for TMV .
SCMV negative strand detection by RT-PCR in resistant maize plants was possible at 6 dpi but no earlier. Both positive and negative intermediate replication RNA strands were detected in the basal proximal region from the inoculation site, suggesting that in this zone, the virus can replicate and have a short distance movement as it does in susceptible maize plants. The direction of the negative strands' movement is suggestive of viruses' well-documented movement along the photoassimilate pathway from a source to a sink leaf . At 12 dpi, both positive and negative RNA forms were also found in the basal regions of the resistant maize plants. At this time, we were unable to identify strands of either polarity in systemic leaves, suggesting a restriction of the virus long distance movement. TMV demonstrated the ability to move from cell-to-cell, from the initial inoculation spot through the plasmodesmata , go through the initial replication step and move as a large replication complex inside the cell through the use of microfilaments, and then between adjacent cells . Potyviral replication complexes have also been observed to move as intracellular vesicles containing replication components [28, 29]. A similar SCMV complex could move a short distance in the inoculated leaf, down to its basal area, and near it insertion to the stem. The presence of negative strands would agree with the replication complex movements proposed for TuMV  and TMV . The viral replicase, RdRp, would replicate the viral genomic RNA if present, in the vesicles, producing the negative strands along its moving path. Inside these moving vesicles, a disrupted interaction between the possible eIF(iso)4E, eIF4E, or eIF4G from recessive resistant genes and the viral VPg could still take place, resulting in resistance towards SCMV similar to other resistant genes for potyviruses [30, 31] and not allowing its translation; hence, the lack of viral proteins (Figure 1B). Nevertheless, such vesicles process of long distance movement along either the phloem sieve tubes or companion cells need to be studied in the host and nonhost resistant genotypes. Long distance movement as a ribonucleotide complex has been suggested by prior research [14, 32–36]. However, further research is needed regarding such vesicles' participation in the long distance movement. Movement as viral particles has been reported for viruses such as the Cucumber mosaic virus  and the Cucumber green mottle virus .
In maize plants, host proteins should be looked at in important anatomical structures connecting leaf blades and stems, such as the ligules , where the transition from replicating genomic RNA complexes to virions that are ready to be transported long distances are likely to take place. The search for proteins that are reportedly involved in these stems and structures' systemic movement will be done in both the non- and host plants for SCMV-VER1.