Seedless fruit may be a pointless waste of resources for a plant, but the economic rewards of growing such crops are considerable. Whereas seedless grapes, bananas and oranges are common groceries, other fruits are less easy to produce. Now, reporting in Proceedings of the National Academy of Sciences , Jia-Long Yao and colleagues have identified mutations in a single gene that result in seedless apples.

Conventional plant breeding has produced a small number of seedless apple varieties such as Wellington Bloomless, Spencer Seedless and Rae Ime, but these varieties produce undersized fruit of poor quality. The apples are not seedless because they cannot make seeded fruit ? in fact, if hand pollinated, they produce fruit with twice the conventional number of seeds. Rather, their flowers are so stunted that they fail to attract insect pollinators.

The blooms of Rae Ime have neither petals nor anthers, these organs being replaced by additional sepals and styles. But lack of pollination is not, on its own, enough to make seedless fruit ? plants require both pollination and fertilization to trigger fruit development. Nevertheless, these stunted flowers reminded Yao and colleagues of a classic Arabidopsis thaliana mutation called pistillata, in which flowers also lack both petals and anthers.

The PISTILLATA gene belongs to the so-called MADS-box family. By a scheme of overlapping expression, these genes direct the development of the four organs that make up a flower: carpels, petals, anthers and styles. Honma and Goto recently reported in Nature that, in the flower, the MADS-box gene products form multi-protein transcription factor complexes, the compositions of which determine their DNA-binding specificities. Inclusion of the PISTILLATA protein in a complex changes its transcriptional targets, converting organs that would otherwise become carpels and styles into petals and anthers, respectively.

Taking the hint from Arabidopsis, Yao and colleagues first identified the apple homologue of PISTILLATA in Granny Smith apples; they share 64% identity at the amino-acid level. In Rae Ime, Wellington Bloomless and Spencer Seedless varieties, however, the authors found transposon insertions that disrupt the gene and prevent it from being transcribed.

This study is the first hint that PISTILLATA is involved in parthenocarpy ? the official name for fruit production without fertilization. Arabidopsis produces a simple type of fruit known as a silique, which develops from the ovaries alone (an organ in which PISTILLATA is never expressed). Apples, on the other hand, form pome fruits with seeds embedded in fleshy tissue derived from sepals, petals and anthers. Somehow PISTILLATA must block the development of pome tissue ? a block that is relieved in normal apples by fertilization.

Seedless fruit varieties are more attractive to consumers and, because they crop without the need for pollinators, they do not depend on insect species during flowering. The identification by Yao and colleagues of the source of seedlessness opens the way for producing seedless strains of commercial apple varieties, whether by conventional breeding or by genetic-manipulation techniques. It may also lead to pipless pears (another pome fruit) and, who knows, perhaps even the stoneless plum.