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Pick a peck of peppers

Just about everyone is familiar with the sweet Bell pepper (Capsicum annuum) found in grocery stores. Likewise, most of us have tasted (like it or not) one of its ‘hot’ cousins like the jalapeno (C. annuum), the tabasco (C. frutescens) or the very hot habanero (C. chinense). Varieties of these large-fruited most-always pungent peppers are favored worldwide as a spice and a vegetable. However, the genus also contains many primitive species of pepper that are rarely seen. These wild types are typically found in ecologically unique (often fragile) environments that are geographically isolated. Most produce very small, but still pungent, fruit.

C. rhomboideum fruit, photo courtesy of G. Barboza

All of the cultivated species of pepper (there are 5 of them) share a common chromosome number of 2n=24. Most of the wild species also share this 2n=24 chromosome number – but there are exceptions. Certain of these wild types may contain 2n=26 chromosomes. A phylogenetic tree of Capsicum species indicates that the chromosome number of wild species has changed over time flip-flopping from 2n=24 to 2n=26, and back again on more than one occasion. The DNA content (genome size) in Capsicum species also varies 3-fold with wild species having 1/2X and 2X the genome size of C. annuum.

The origin and subsequent fate of the 13th chromosome pair in wild Capsicum species remains unclear as does the basis for the large shifts in genome size. The independent evolution of 2n=24 and 2n=26 species makes them particularly useful in the study of chromosome/genome evolution and genome architecture in the genus Capsicum. A better understanding of genome evolution in Capsicum, using wild species, many of which contain agriculturally important traits, will enable the use of such information to trace the evolution of genes and gene complex in this important genus.

We report here the genome sequence of the n=13 chromosome Capsicum rhomboideum (Dunal) Kuntze, a species bearing small, red, non-pungent fruit and having a characteristic yellow corolla. This species is native to Mexico, Central America and northwestern South America to northern Peru. A phylogenetic tree places C. rhomboideum near the base of that tree making this species one of the species most distantly related to C. annum.

Count the 13 chromosomes for yourself in the map below, and don't forget to check out the assembly page!

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