The role of APETALA1 in petal number robustness

Abstract

Invariant floral forms are important for reproductive success and robust to natural perturbations. Petal number, for example, is invariant in Arabidopsis thaliana flowers. However, petal number varies in the closely related species Cardamine hirsuta, and the genetic basis for this difference between species is unknown. Here we show that divergence in the pleiotropic floral regulator APETALA1 (AP1) can account for the species-specific difference in petal number robustness. This large effect of AP1 is explained by epistatic interactions: A. thaliana AP1 confers robustness by masking the phenotypic expression of quantitative trait loci controlling petal number in C. hirsuta. We show that C. hirsuta AP1 fails to complement this function of A. thaliana AP1, conferring variable petal number, and that upstream regulatory regions of AP1 contribute to this divergence. Moreover, variable petal number is maintained in C. hirsuta despite sufficient standing genetic variation in natural accessions to produce plants with four-petalled flowers.

Developmental stochasticity and variation in floral phyllotaxis

“…Although stochasticity exists ubiquitously in the developmental process, the degree of noise required to change the morphology is different among species and organs. Genetic basis of robust ranges against perturbations has been evaluated in studies on the Brassicaceae species Cardamine hirsuta L. (Monniaux et al 2016 , 2018 ; Pieper et al 2016 ). Most of the Brassicaceae species, including A. thaliana , show a stable floral construct with four sepals and four petals.…”

“…The variation depends on environmental perturbations such as day length and temperature, and is a heritable phenotype (McKim et al 2017 ; Monniaux et al 2016 ; Pieper et al 2016 ). APETALA1 ( AP1 ), which establishes floral meristem identity and acts as one of the A-class genes in Brassicaceae (Litt 2007 ), has been shown to be involved in the difference in the petal number variation between C. hirsuta and A. thaliana (Monniaux et al 2018 ). These studies suggest a genetic basis of noise buffering in Brassicaceae species with stable petal numbers, and evolutionary change in the floral stability of C. hirsuta by releasing cryptic variation (Monniaux et al 2018 ).…”

Protein Farnesylation Takes Part in Arabidopsis Seed Development

“…ap1 , cal and ap1 / cal knock-out plants display more severe floral phenotype than era1 suggesting that the non-farnesylated proteins present in era1 flower maintain some functionality. Because, AP1 is also involved in flower organ number determination ( Monniaux et al, 2018 ) and its actions are enhanced through CAL ( Ye et al, 2016 ), the lack of farnesylation of both proteins may lead, in cooperation with AtJ2/AtJ3, to the abnormal number of carpels observed in era1-8 . Investigating Arabidopsis transgenic ap1/cal/AtJ2/AtJ3 plants co-expressing non-farnesylatable forms of AP1, CAL, AtJ2 and AtJ3 (i.e., mutated CaaX-boxes) with their specific transcriptional promoters may unravel the involvement of protein farnesylation in carpel number determination, nevertheless we cannot exclude that other unidentified CaaX-proteins make more complex the mechanism leading to this era1-8 singular phenotype.…”

CRISPR/Cas9-Mediated Mutagenesis of RCO in Cardamine hirsuta

“…Over the past few years Cardamine hirsuta, a small crucifer related to the reference plant Arabidopsis thaliana, has emerged as a powerful model system for comparative developmental studies in plants. Both species belong to Lineage I of the Brassicaceae, and parallel genetic studies have provided a powerful platform to identify the molecular causes of trait diversity between these two species and for understanding the morphogenetic basis [1][2][3][4][5][6]. Studies of leaf development in particular have led to major advances in identifying both causal genes and regulatory sequences for the diversification of form and the broader logic through which morphological evolution proceeds [2,[7][8][9][10][11].…”