The T-DNA moves into the nucleus of the plant and begins to integrate into the plants' chromosome. The gene is then transiently expressed through RNA synthesis from appropriate promoter sequences in all transfected cells (no selection for stable integration is performed). The plant can be monitored for a possible effect in the phenotype, subjected to experimental conditions or harvested and used for purification of the protein of interest. Many plant species can be processed using this method, but the most common ones are "Nicotiana benthamiana" and less often, "Nicotiana tabacum". Transient expression in cultured plant cell packs is a new procedure, recently patented by the Fraunhofer Institute IVV, Germany. For this technique, suspension cultured cells of tobacco (e.g.: NT1 or BY2 cell lines of "Nicotiana tabacum") are immobilised by filtration onto a porous support to form a well-aerated cell pack, then incubated with recombinant "Agrobacterium" for a time to allow T-DNA transfer, before refiltration to remove excess bacteria and liquid. Incubation of the cell pack in a humid environment for time periods up to several days allows transient expression of protein. Secreted proteins can be washed out of the cell pack by application of buffer and further filtration. It's quite common to coinfiltrate the "Agrobacterium" carrying the construct of interest together with another "Agrobacterium" carrying a silencing suppressor protein gene such as the one encoding the p19 protein from the plant pathogenic Tomato bushy stunt virus (TBSV), or the NSs protein  from tomato spotted wilt virus (TSWV). TBSV was first discovered in 1935 in tomatoes and results in plants with stunted growth and deformed fruits. TSWV was discovered in tomatoes in Australia in 1915, and for many years was the only member of what is now known as genus "Tospovirus", family "Bunyaviridae". In order to defend itself against viruses and other pathogens that introduce foreign nucleic acids into their cells, plants have developed a system of post-transcriptional gene silencing (PTGS) where small interfering RNAs are produced from double-stranded RNA in order to create a sequence specific degradation pathway that efficiently silence non-native genes. Many plant viruses have developed mechanisms that counter the plants PTGS-systems by evolving proteins, such as p19 and NSs, that interfere with the PTGS-pathway at different levels.