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Heterochronic developmental shifts underlie floral diversity within Jaltomata (Solanaceae).

ABSTRACT: BACKGROUND:Heterochronic shifts during mid- to late stages of organismal development have been proposed as key mechanisms generating phenotypic diversity. To determine whether late heterochronic shifts underlie derived floral morphologies within Jaltomata (Solanaceae)-a genus whose species have extensive and recently evolved floral diversity-we compared floral development of four diverse species (including an ambiguously ancestral or secondarily derived rotate, two putatively independently evolved campanulate, and a tubular morph) to the ancestral rotate floral form, as well as to an outgroup that shares this ancestral floral morphology. RESULTS:We determined that early floral development (< 1 mm bud diameter, corresponding to completion of organ whorl initiation) is very similar among all species, but that different mature floral forms are distinguishable by mid-development (> 1 mm diameter) due to differential growth acceleration of corolla traits. Floral ontogeny among similar mature rotate forms remains comparable until late stages, while somewhat different patterns of organ growth are found between species with similar campanulate forms. CONCLUSIONS:Our data suggest shared floral patterning during early-stage development, but that different heterochronic shifts during mid- and late-stage development contribute to divergent floral traits. Heterochrony thus appears to have been important in the rapid and repeated diversification of Jaltomata flowers.

SUBMITTER: Kostyun JL

PROVIDER: S-EPMC5651583 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Heterochronic developmental shifts underlie floral diversity within <i>Jaltomata</i> (Solanaceae).

Kostyun Jamie L JL Preston Jill C JC Moyle Leonie C LC

EvoDevo 20171023

<h4>Background</h4>Heterochronic shifts during mid- to late stages of organismal development have been proposed as key mechanisms generating phenotypic diversity. To determine whether late heterochronic shifts underlie derived floral morphologies within <i>Jaltomata</i> (Solanaceae)-a genus whose species have extensive and recently evolved floral diversity-we compared floral development of four diverse species (including an ambiguously ancestral or secondarily derived rotate, two putatively inde ...[more]

PMID: 29075434

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Project description:BackgroundPolyploidy has played a major role in angiosperm evolution. Previous studies have examined polyploid phenotypes in comparison to their extant progenitors, but not in context of predicted progenitor phenotypes at allopolyploid origin. In addition, differences in the trends of polyploid versus diploid evolution have not been investigated. We use ancestral character-state reconstructions to estimate progenitor phenotype at allopolyploid origin to determine patterns of polyploid evolution leading to morphology of the extant species. We also compare trends in diploid versus allopolyploid evolution to determine if polyploidy modifies floral evolutionary patterns.ResultsPredicting the ancestral phenotype of a nascent allopolyploid from reconstructions of diploid phenotypes at the time of polyploid formation generates different phenotype predictions than when extant diploid phenotypes are used, the outcome of which can alter conclusions about polyploid evolution; however, most analyses yield the same results. Using ancestral reconstructions of diploid floral phenotypes indicate that young polyploids evolve shorter, wider corolla tubes, but older polyploids and diploids do not show any detectable evolutionary trends. Lability of the traits examined (floral shape, corolla tube length, and corolla tube width) differs across young and older polyploids and diploids. Corolla length is more evolutionarily labile in older polyploids and diploids. Polyploids do not display unique suites of floral characters based on both morphological and color traits, but some suites of characters may be evolving together and seem to have arisen multiple times within Nicotiana, perhaps due to the influence of pollinators.ConclusionsYoung polyploids display different trends in floral evolution (shorter, wider corolla tubes, which may result in more generalist pollination) than older polyploids and diploids, suggesting that patterns of divergence are impacted by the early consequences of allopolyploidy, perhaps arising from genomic shock and/or subsequent genome stabilization associated with diploidization. Convergent evolution in floral morphology and color in Nicotiana can be consistent with pollinator preferences, suggesting that pollinators may have shaped floral evolution in Nicotiana.

Project description:BACKGROUND AND AIMS:Apomixis is an asexual reproductive mode via seeds that generate maternal clonal progenies. Although apomixis in grasses is mainly expressed at the polyploid level, some natural diploid genotypes of Paspalum rufum produce aposporous embryo sacs in relatively high proportions and are even able to complete apomixis under specific conditions. However, despite the potential for apomixis, sexuality prevails in diploids, and apomixis expression is repressed for an as yet undetermind reason. Apomixis is thought to derive from a deregulation of one or a few components of the sexual pathway that could be triggered by polyploidy and/or hybridization. The objectives of this work were to characterize and compare the reproductive development and the timing of apospory initial (AI) emergence between diploid genotypes with potential for apomixis and facultative apomictic tetraploid cytotypes of P. rufum. METHODS:Reproductive characterization was performed by cytoembryological observations of cleared ovaries and anthers during all reproductive development steps and by quantitative evaluation of the ovule growth parameters. KEY RESULTS:Cytoembryological observations showed that in diploids, both female and male reproductive development is equally synchronized, but in tetraploids, megasporogenesis and early megagametogenesis are delayed with respect to microsporogenesis and early microgametogenesis. This delay was also seen when ovary growth was taken as a reference parameter. The analysis of the onset of AIs revealed that they emerge during different developmental periods depending on the ploidy level. In diploids, the AIs appeared along with the tetrad (or triad) of female meiocytes, but in tetraploids they appeared earlier, at the time of the megaspore mother cell. In both cytotypes, AIs can be seen even during megagametogenesis. CONCLUSIONS:Overall observations reveal that female sexual reproductive development is delayed in tetraploids as compared with diploid genotypes, mainly at meiosis. In tetraploids, AIs appear at earlier sexual developmental stages than in diploids, and they accumulate up to the end of megasporogenesis. The longer extension of megasporogenesis in tetraploids could favour AI emergence and also apomixis success.

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Heterochronic developmental shifts underlie floral diversity within Jaltomata (Solanaceae).

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Heterochronic developmental shifts underlie floral diversity within <i>Jaltomata</i> (Solanaceae).

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