Physiological changes besides the enhancement of pigmentation in Petunia hybrida caused by overexpression of PhAN2, an R2R3-MYB transcription factor.

Abstract

Ectopic expression of PhAN2 in vegetative tissue can improve regeneration and adventitious rooting but inhibit axillary bud outgrowth of petunia, while overexpression specifically in flowers could shorten longevity. Anthocyanin 2 has been only treated as a critical positive regulation factor of anthocyanin biosynthesis in petunia flowers. To determine if this gene had other functions in plant growth, we overexpressed this gene in an an2 mutant petunia cultivar driven by promoters with different strengths or tissue specificity. Various physiological processes of transformants in different growth stages and environments were analyzed. Besides the expected pigmentation improvement in different tissues, the results also showed that ectopic expression of AN2 could improve the regeneration skill but inhibit the axillary bud germination of in vitro plants. Moreover, the rooting ability of shoot tips of transformants was significantly improved, while some transgenic lines' flower longevity was shortened. Gene expression analysis showed that the transcripts level of AN2, partner genes anthocyanin 1 (AN1), anthocyanin 11 (AN11), and target gene dihydroflavonol 4-reductase (DFR) was altered in the different transgenic lines. In addition, ethylene biosynthesis-related genes 1-aminocyclopropane-1-carboxylic acid synthase (ACS1) and ACC oxidase (ACO1) were upregulated in rooting and flower senescence processes but at different time points. Overall, our data demonstrate that the critical role of this AN2 gene in plant growth physiology may extend beyond that of a single activator of anthocyanin biosynthesis.