Physalis Blog Post
Biology Minute: Husk Formation
The Physalis genus is known for the husks that surround its fruit, an attribute that offers protection from pests and disease, increases shelf life of berries, and in the case of Chinese lantern, adds ornamental value. Although commonly associated with Physalis, these husks also form in other solanaceae genera, such as Maragaranthu, Nicandra, Przewalskia, and Withania. With the widespread appearance of this trait within the solanaceae family, the question arises of how this trait develops.
This phenomenon, termed Inflated Calyx Syndrome (ICS), occurs when the sepals continue to grow after pollination and engulf the fruit in an inflated husk. But what causes this to happen? One possibility is that this trait is at least partially controlled by members of the MADS-box gene family, a family known to determine floral organ identity.
In 2005 He and Saedler demonstrated that a MADS-Box gene called MPF2, played a key role in the incidence of ICS. They demonstrated this by using RNA interference, a technique used to “knock down” gene expression. When MPF2 was knocked down in Physalis pubescens the sepal size was reduced. However an unexpected result also occurred: the flowers pollen was unviable rendering them male-sterile. A connection between male fertility and ICS would indicate a strong selective pressure towards ICS formation, however many species without ICS exist. This brings to question whether MPF2 is the main genetic controller of ICS, or if it just one player in a complex pathway.
So how does this trait develop? Although many hypotheses have been formed the true genetic control of ICS still remains a mystery.
For further reading check out this journal article:
He, C., & Saedler, H. (2005). Heterotopic expression of MPF2 is the key to the evolution of the Chinese lantern of Physalis, a morphological novelty in Solanaceae. Proceedings of the National Academy of Sciences of the United States of America, 102(16), 5779–5784. http://doi.org/10.1073/pnas.0501877102