A cDNA clone, STMADS11, encoding a new MADS-box protein was isolated from Solanum tuberosum L. (potato). Expression of STMADS11 was found in all vegetative organs of the plant, but not in floral tissues. The expression was also detected in all developmental stages, from tuber sprouts to mature plants, reaching a maximum in well-developed organs. However, the level of STMADS11 mRNA was low in tissues such as resting tuber or sprouts developed in the cold, where the metabolic activity is reduced. "In situ" hybridizations performed on leaf and stem sections showed that the STMADS11 transcript is mainly associated with vascular bundles. Cladistic analysis arising from amino acid sequence comparison revealed that STMADS11 shows the highest similarity to STMADS16, another vegetative MADS-box gene from potato, and to the previously reported "orphan" genes AGL15 and AGL17 from Arabidopsis thaliana. Possible implications of these data in relation to STMADS11 function are discussed.

Morphological novelties arise through changes in development, but the underlying causes of such changes are largely unknown. In the genus Physalis, sepals resume growth after pollination to encapsulate the mature fruit, forming the "Chinese lantern," a trait also termed inflated-calyx syndrome (ICS). STMADS16, which encodes a MADS-box transcription factor, is expressed only in vegetative tissues in Solanum tuberosum. Its ortholog in Physalis pubescens, MPF2, is expressed in floral tissues. Knockdown of MPF2 function in Physalis by RNA interference (RNAi) reveals that MPF2 function is essential for the development of the ICS. The phenotypes of transgenic S. tuberosum plants that overexpress MPF2 or STMADS16 corroborate these findings: these plants display enlarged sepals. Although heterotopic expression of MPF2 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 Physalis knockdown lines are male sterile. Thus, heterotopic expression of MPF2 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 MPF2 and STMADS16 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 MPF2 underline the importance of recruitment of preexisting transcription factors in the evolution of novel floral traits.