Due to unknown factors, internal standardization with H. vulgare 'Sultan' may not be appropriate for DNA content determinations of Gossypium. The current DNA content estimates support accepted cytogenetic divisions of the genus. Gossypium is a genus that exhibits genome constancy both through speciation within genomic groups and allopolyploidization.

The development of a formulation for siRNA delivery enables posttranscriptional gene silencing in plants with a simple spray application.

Foliar application of dsRNA to elicit an RNA interference (RNAi) response is currently under consideration as a crop protection strategy. To access the RNAi machinery of a plant, foliarly applied dsRNAs must traverse the plant cuticle, avoid nuclease degradation, and penetrate the cell wall and plasma membrane. Application methods and co-formulants have been identified by Bayer Crop Science researchers and others that can help bypass barriers to dsRNA uptake in plants leading to an RNAi response in greenhouse grown, young plants and cell cultures. However, these advances in dsRNA delivery have yet to yield systemic RNAi silencing of an endogenous gene target required for product concepts such as weed control. Systemic RNAi silencing in plants has only been observed with the GFP transgene in Nicotiana benthamiana. Because biologically meaningful whole plant RNAi has not been observed for endogenous gene products in N. benthamiana or in other plant species tested, under growing conditions including field production, the regulatory risk assessment of foliarly applied dsRNA-based products should not consider exposure scenarios that include systemic response to small RNAs in treated plants.

The Initiation of RNA interference (RNAi) by topically applied double stranded RNA (dsRNA) has potential applications for plant functional genomics, crop improvement and crop protection. The primary obstacle for the development of this technology is efficient delivery of RNAi effectors. The plant cell wall is a particularly challenging barrier to the delivery of macromolecules. Many of the transfection agents that are commonly used with animal cells produce nanocomplexes that are significantly larger than the size exclusion limit of the plant cell wall. Utilizing a class of very small nanoparticles called carbon dots, a method of delivering siRNA into the model plant Nicotiana benthamiana and tomato is described. Low-pressure spray application of these formulations with a spreading surfactant resulted in strong silencing of GFP transgenes in both species. The delivery efficacy of carbon dot formulations was also demonstrated by silencing endogenous genes that encode two sub-units of magnesium chelatase, an enzyme necessary for chlorophyll synthesis. The strong visible phenotypes observed with the carbon dot facilitated delivery were validated by measuring significant reductions in the target gene transcript and/or protein levels. Methods for the delivery of RNAi effectors into plants, such as the carbon dot formulations described here, could become valuable tools for gene silencing in plants with practical applications in plant functional genomics and agriculture.

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