Abstract
The fruit of Physalis has a berry and a novelty called inflated calyx syndrome (ICS, also named the ‘Chinese lantern’). Elucidation of the underlying developmental mechanisms of fruit diversity demands an efficient gene functional inference platform. Here, we tested the application of the tobacco rattle virus (TRV)-mediated gene-silencing system in Physalis floridana. First, we characterized the putative gene of a phytoene desaturase in P. floridana (PfPDS). Infecting the leaves of the Physalis seedlings with the PfPDS-TRV vector resulted in a bleached plant, including the developing leaves, floral organs, ICS, berry, and seed. These results indicated that a local VIGS treatment can efficiently induce a systemic mutated phenotype. qRT-PCR analyses revealed that the bleaching extent correlated to the mRNA reduction of the endogenous PfPDS. Detailed comparisons of multiple infiltration and growth protocols allowed us to determine the optimal methodologies for VIGS manipulation in Physalis. We subsequently utilized this optimized VIGS methodology to downregulate the expression of two MADS-box genes, MPF2 and MPF3, and compared the resulting effects with gene-downregulation mediated by RNA interference (RNAi) methods. The VIGS-mediated gene knockdown plants were found to resemble the mutated phenotypes of floral calyx, fruiting calyx and pollen maturation of the RNAi transgenic plants for both MPF2 and MPF3. Moreover, the two MADS-box genes were appeared to have a novel role in the pedicel development in P. floridana. The major advantage of VIGS-based gene knockdown lies in practical aspects of saving time and easy manipulation as compared to the RNAi. Despite the lack of heritability and mosaic mutation phenotypes observed in some organs, the TRV-mediated gene silencing system provides an alternative efficient way to infer gene function in various developmental processes in Physalis, thus facilitating understanding of the genetic basis of the evolution and development of the morphological diversities within the Solanaceae.
Highlights
IntroductionIn this genus, the calyx enlarges rapidly into a Chinese lantern structure as the berry develops
Bleached phenotypes are easy to observe, and this is the primary reason that phytoene desaturase gene (PDS) is used as a reporter for the successful application of Virus-induced gene silencing (VIGS)
It putatively encoded a protein consisting of 582 amino acids, sharing 95% and 91% sequence identities with SlyPDS from S. lycopersicum and NbePDS from N. benthamiana, respectively
Summary
In this genus, the calyx enlarges rapidly into a Chinese lantern structure as the berry develops. The calyx enlarges rapidly into a Chinese lantern structure as the berry develops This enlarged calyx, called inflated calyx syndrome (ICS), encloses the entire berry. This ICS trait is a postfloral novelty within the Solanaceae. Some differentially expressed genes between tomatillo accessions with large and small berries were isolated, and their expression in response to developmental cues might explain their potential roles in berry development and size control [6]. Physalis is emerging as a model plant in evolutionary biology for the origin of the morphological novelties and natural variation of the complex traits [6]. The elucidation of the complete genetic architecture responsible for ICS and berry size is still challenging, owing to many technological restrictions
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