Model for regulatory events underlying fruit set mainly mediated by auxin and gibberellin.

<p>(A) After pollination, the increase of auxin and GA biosynthesis and response will trigger fruit initiation. And the elevated auxin and GA would inhibit ethylene biosynthesis and response which negatively regulate fruit set. Auxin stimulates GA biosynthesis gene <i>GA20ox1</i> via down-regulating <i>KNOX</i> (<i>LeT6</i>, <i>LeT12</i>) in partially, subsequently influences GA response by regulating <i>GID1</i> and <i>GRAS</i>. Some Aux/IAAs may be degraded by the 26S proteasome and in turn, the transcripts are increased via feedback regulation to fine-tune auxin response. Some ARFs (<i>ARF4</i>, <i>ARF9</i>) are up-regulated which could promote auxin signaling cascades. In addition, auxin response may be mediated by GA via down-regulation of <i>IAA9</i> and <i>ARF2</i> during fruit set. Accordingly, events that the activation of carbohydrate metabolism, cell division and expansion as well as the down-regulation of <i>MADS-box</i> occur to promote fruit set process. (B) After 2, 4-D application, <i>KNAT3</i> displayed down-regulation, which would interact with BLH1, thus negatively regulating parthenocarpy. In the present of GA, the transcripts of <i>DELLA</i> and <i>GID2</i> are regulated via feedback to fine-tune GA response. GA application decreased the transcripts of <i>IAA9</i> and <i>ARF8B</i>, and then led to parthenocarpy. Moreover, other factors such as <i>GRAS</i>, <i>AGL66</i> and <i>AGO10</i>, which are down-regulated after hormone application, also seem to have a regulatory role in parthenocarpy. The red and green frame shows up- and down-regulation, respectively. The red line arrow and the green line behind represent positive and negative regulation, respectively. The regular arc line represents feedback regulation. Dashed line shows suggested interactions.