lepidium-like, a Naturally Occurring Mutant of Capsella bursa-pastoris, and Its Implications on the Evolution of Petal Loss in Cruciferae

Abstract

Naturally occurring mutants whose phenotype recapitulates the changes that distinguish closely related species are of special interest from the evolutionary point of view. They can give a key about the genetic control of the changes that led to speciation. In this study, we described lepidium-like (lel), a naturally occurring variety of an allotetraploid species Capsella bursa-pastoris that is characterized by the typical loss of all four petals. In some cases, one or two basal flowers in the raceme had one or two small petals. The number and structure of other floral organs are not affected. Our study of flower development in the mutant showed that once initiated, petals either cease further development and cannot be traced in anthetic flowers or sometimes develop to various degrees. lel plants showed an earlier beginning of floral organ initiation and delayed petal initiation compared to the wild-type plants. lel phenotype has a wide geographical distribution, being found at the northern extremity of the species range as well as in the central part. The genetic analysis of inheritance demonstrated that lel phenotype is controlled by two independent loci. While the flower in the family Cruciferae generally has a very stable structure (i.e., four sepals, four petals, six stamens, and two carpels), several deviations from this ground plan are known, in particular in the genus Lepidium, C. bursa-pastoris is an emerging model for the study of polyploidy (which is also very widespread in Cruciferae); the identification and characterization of the apetalous mutant lays a foundation for further research of morphological evolution in polyploids.

Mechanical Forces in Floral Development

“…This point of view could explain the absence of petals in the ptl mutant even if the target gene is acting in a different whorl. However, other mechanisms may be at play leading to petal loss, such as the homeotic transformation of petals in stamens in the spe mutant of Capsella bursa-pastoris [ 69 ] or the apetalous lel mutant, where loss of petals is the result of a progressive abortion [ 70 ].…”

Molecular phylogenetics and morphology reveal the Plettkea lineage including several members of Arenaria and Pycnophyllopsis to be a clade of 21 South American species nested within Stellaria (Caryophyllaceae, Alsineae)

“…2002) or it could be associated with the evolution of autogamy (Pieper & al. 2016; Klepikova & al. 2021).…”

“…2002) or it could be associated with the evolution of autogamy (Pieper & al. 2016;Klepikova & and Pycnophyllopsis along with a number of taxa currently classified as Arenaria and further specimens that could not be identified using the available Floras, were recovered as part of a strongly deviant clade including the members of core Stellaria sensu Sharples & Tripp (2019) and Arabi & al. (2022).…”