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Floral organ size, especially the size of the corolla, plays an important role in plant reproduction by facilitating pollination efficiency. Previous studies have outlined a hypothesized organ size pathway. However, the expression and function of many of the genes in the pathway have only been investigated in model diploid species; therefore, it is unknown how these genes interact in polyploid species. Although correlations between ploidy and cell size have been shown in many systems, it is unclear whether there is a difference in cell size between naturally occurring and synthetic polyploids. To address these questions comparing floral organ size and cell size across ploidy, we use natural and synthetic polyploids of Nicotiana tabacum (Solanaceae) as well as their known diploid progenitors. We employ a comparative transcriptomics approach to perform analyses of differential gene expression, focusing on candidate genes that may be involved in floral organ size, both across developmental stages and across accessions. We see differential expression of several known floral organ candidate genes including ARF2, BIG BROTHER, and GASA/GAST1. Results from linear models show that ploidy, cell width, and cell number positively influence corolla tube circumference; however, the effect of cell width varies by ploidy, and diploids have a significantly steeper slope than both natural and synthetic polyploids. These results demonstrate that polyploids have wider cells and that polyploidy significantly increases corolla tube circumference. 

Datura stramoniumis a pharmacologically and evolutionarily important plant species in the family Solanaceae. Stable transformation methodology of this species would be advantageous for future genetic studies.

In vitro plant regeneration andAgrobacterium tumefaciens–mediated transformation techniques were developed forD. stramoniumbased on methods reported for tomato. A binary vector containingpAtUBQ10::erGFPwas used for transformation.

We recovered primary transformants harboring the green fluorescent protein (GFP) transgene that resulted in expression of fluorescence in all tissues analyzed. Transformants were allowed to self‐pollinate, and two of five progeny contained theGFPtransgene and displayed fluorescence identical to the primary transformants.

We have demonstrated the first stable transformation in the genusDatura. This is a key first step to study the genetic basis of traits in this evolutionarily interesting species.

 

Understanding the genetic basis of natural phenotypic variation is of great importance, particularly since selection can act on this variation to cause evolution. We examined expression and allelic variation in candidate flowering time loci inBrassica rapaplants derived from a natural population and showing a broad range in the timing of first flowering. The loci of interest were orthologs of the Arabidopsis genesFLCandSOC1(BrFLCandBrSOC1, respectively), which in Arabidopsis play a central role in the flowering time regulatory network, withFLCrepressing andSOC1promoting flowering. InB. rapa, there are four copies ofFLCand three ofSOC1. Plants were grown in controlled conditions in the lab. Comparisons were made between plants that flowered the earliest and latest, with the difference in average flowering time between these groups ∼30 days. As expected, we found that total expression ofBrSOC1paralogs was significantly greater in early than in late flowering plants. Paralog-specific primers showed that expression was greater in early flowering plants in theBrSOC1paralogsBr004928, Br00393andBr009324, although the difference was not significant inBr009324. Thus expression of at least 2 of the 3BrSOC1orthologs is consistent with their predicted role in flowering time in this natural population. Sequences of the promoter regions of theBrSOC1orthologs were variable, but there was no association between allelic variation at these loci and flowering time variation. For theBrFLCorthologs, expression varied over time, but did not differ between the early and late flowering plants. The coding regions, promoter regions and introns of these genes were generally invariant. Thus theBrFLCorthologs do not appear to influence flowering time in this population. Overall, the results suggest that even for a trait like flowering time that is controlled by a very well described genetic regulatory network, understanding the underlying genetic basis of natural variation in such a quantitative trait is challenging.