Comparative analysis of corolla tube development across three closely related Mimulus species with different pollination syndromes

Abstract

Fusion of petals to form a corolla tube is considered a key innovation contributing to the diversification of many flowering plant lineages. Corolla tube length often varies dramatically among species and is a major determinant of pollinator preference. However, our understanding of the developmental dynamics underlying corolla tube length variation is very limited. Here we examined corolla tube growth in the Mimulus lewisii species complex, an emerging model system for studying the developmental genetics and evo‐devo of pollinator‐associated floral traits. We compared developmental and cellular processes associated with corolla tube length variation among the bee‐pollinated M. lewisii, the hummingbird‐pollinated Mimulus verbenaceus, and the self‐pollinated Mimulus parishii. We found that in all three species, cell size is non‐uniformly distributed along the mature tube, with the longest cells just distal to the stamen insertion site. Differences in corolla tube length among the three species are not associated with processes of organogenesis or early development but are associated with variation in multiple processes occurring later in development, including the location and duration of cell division and cell elongation. The tube growth curves of the small‐flowered M. parishii and large‐flowered M. lewisii are essentially indistinguishable, except that M. parishii tubes stop growing earlier at a smaller size, suggesting a critical role of heterochrony in the shift from outcrossing to selfing. These results not only highlight the developmental process associated with corolla tube variation among species but also provide a baseline reference for future developmental genetic analyses of mutants or transgenic plants with altered corolla tube morphology in this emerging model system.

Modular regulation of floral traits by aPRE1homolog inMimulus verbenaceus: implications for the role of pleiotropy in floral integration

“…To determine whether the floral organ length changes in the MvPRE1 RNAi and overexpression lines are due to change in cell number or cell length, we profiled cell number and size along the dorsal side of the corolla tube of open flowers from the wild type (MvBL), RNAi line 4 (RNAi-4), and overexpression line 10 (OE-10). Consistent with a previous study [ 39 ], we found that in the wild-type MvBL, cell length increases gradually from the base of the corolla tube to the stamen insertion site, then plateaus for ~50 cells with maximal length before gradually decreasing towards the distal end ( Fig. 5a,d ).…”

“…5-mm, 15-mm, 20-mm, and 35-mm), and found that MvPRE1 is the only PRE -like gene with readily detectable expression across multiple floral developmental stages, with peak expression level at the 20-mm stage ( Fig. 2b ) when the corolla tube is rapidly growing through cell elongation [ 39 ]. Phylogenetic analysis suggests that MvPRE1 is closely related to tomato SlPRE1/Style2.1 and SlPRE2 ( Fig.…”

“…To determine whether the phenotypic differences between the wild type and the transgenic lines are due to cell number or cell size, we profiled the cell number and cell length along the dorsal side of the corolla tube ( Fig. 1c ) of mature flowers using a compound light microscope, following [ 39 ].…”

Delayed differentiation of epidermal cells walls can underlie pedomorphosis in plants: the case of pedomorphic petals in the hummingbird-pollinated Caiophora hibiscifolia (Loasaceae, subfam. Loasoideae) species

“…Corolla morphology is particularly important to plant–pollinator interactions, as it determines the location on which pollen is placed and picked up from the pollinator body [ 11 ]. Heterochrony was involved in adaptation of corolla morphology to different pollinators in lineages as diverse as Delphinium (Ranunculaceae) [ 14 ], Aquilegia (Ranunculaceae) [ 28 ], Calceolaria (Calceolariaceae) [ 38 ] and Mimulus (Phyrmaceae) [ 15 ].…”

Flower size constrains reproductive potential in three Andean monkeyflower species

“…In developmental terms, style length is determined by the number of cells that conform to this structure (Bartrina et al, 2011). Possibly, the observed covariation between corolla tube length and style length depends on the number of cells in the meristem (Raghavan, 2000) and cell elongation (Gurung et al, 2021). Transitions from selfing to outcross pollination, which probably are associated with style and corolla tube lengths, have been described for species of the Erythranthe section (Beardsley et al, 2003).…”