Description:
<jats:p>
Morphological novelties arise through changes in development, but the underlying causes of such changes are largely unknown. In the genus
<jats:italic>Physalis</jats:italic>
, sepals resume growth after pollination to encapsulate the mature fruit, forming the “Chinese lantern,” a trait also termed inflated-calyx syndrome (ICS).
<jats:italic>STMADS16</jats:italic>
, which encodes a MADS-box transcription factor, is expressed only in vegetative tissues in
<jats:italic>Solanum tuberosum</jats:italic>
. Its ortholog in
<jats:italic>Physalis pubescens</jats:italic>
,
<jats:italic>MPF2</jats:italic>
, is expressed in floral tissues. Knockdown of MPF2 function in
<jats:italic>Physalis</jats:italic>
by RNA interference (RNAi) reveals that MPF2 function is essential for the development of the ICS. The phenotypes of transgenic
<jats:italic>S. tuberosum</jats:italic>
plants that overexpress
<jats:italic>MPF2</jats:italic>
or
<jats:italic>STMADS16</jats:italic>
corroborate these findings: these plants display enlarged sepals. Although heterotopic expression of
<jats:italic>MPF2</jats:italic>
is crucial for ICS, remarkably, fertilization is also required. Although the ICS is less prominent or absent in the knockdown transgenic plants, epidermal cells are larger, suggesting that MPF2 exerts its function by inhibiting cell elongation and promoting cell division. In addition, severely affected
<jats:italic>Physalis</jats:italic>
knockdown lines are male sterile. Thus, heterotopic expression of
<jats:italic>MPF2</jats:italic>
in floral tissues is involved in two novel traits: expression of the ICS and control of male fertility. Sequence differences between the promoter regions of the
<jats:italic>MPF2</jats:italic>
and
<jats:italic>STMADS16</jats:italic>
genes perhaps reflect exposure to different selection pressures during evolution, and correlate with the observed differences in their expression patterns. In any case, the effects of heterotopic expression of
<jats:italic>MPF2</jats:italic>
underline the importance of recruitment of preexisting transcription factors in the evolution of novel floral traits.
</jats:p>