Genetic architecture of spatially complex color patterning in hybrid Mimulus

Interspecies hybridization generates inter-genomic interactions, which may result in unique traits not seen in either parent species. Here we explore the genetic basis of two types of floral pigment phenotypes, in hybrids between monkeyflower species Mimulus cupreus and M. luteus var. variegatus. Mimulus cupreus has abundant yellow carotenoid pigmentation in its petal lobes, while M. l. variegatus has a derived reduction in carotenoid intensity. Thus, as expected, carotenoid intensity segregates in an F2 hybrid population. More surprisingly, both species appear to have petal lobes solidly and identically covered in magenta anthocyanin pigment (leading to an orange color in the high-carotenoid species M. cupreus ), yet F1 and F2 hybrids exhibit novel and complex spatial patterns of anthocyanin spotting. A rare yellow morph of M. cupreus , which lacks petal anthocyanins, also generates spatially patterned offspring when hybridized with M. l. variegatus . We use this cross, together with newly developed genomic and image analysis tools, to investigate the genetic architecture of color and pattern variation in an F2 hybrid population. We report that the non-patterned carotenoid reduction in M. l. variegatus is genetically simple, and is explained by a single QTL which contains the Beta-carotene hydroxylase-1 ( BCH1 ) gene. HPLC results show that beta-carotene content differs between dark yellow and light yellow petals, which supports a causal role for BCH1 . The hybrid-specific anthocyanin patterning phenotypes are more complex, with one QTL of large effect and four detectable QTLs of small effect. These results illustrate how different types of traits may have predictably distinct genetic architectures, and provide candidate genomic regions for investigating the molecular mechanisms of both simple and complex floral color patterning. ### Competing Interest Statement The authors have declared no competing interest.