Genetic control of the lateral petal shape and identity of asymmetric flowers in mungbean (Vigna radiata L.).

Broad diversity of flowers in Fabaceae provides a good system to investigate development and evolution of floral symmetry in higher plants. Many studies have demonstrated a conserved mechanism controlling development of zygomorphic flower during last decades. However, the molecular basis of how asymmetric flower established is largely unknown. In this study, we characterized mutants named keeled wings (kw) in mungbean (Vigna radiata L.), which is a legume species with asymmetric flowers. Compared to those in the wild type plants, the lateral petals were ventralized in the kw mutants. Map-based cloning showed that KW was VrCYC3 gene in mungbean, the ortholog of Lotus japonicus CYC3 (LjCYC3) and Pisum sativum CYC3 (PsCYC3). In addition, another two CYC-like genes named VrCYC1 and VrCYC2 were identified from mungbean genome. The three CYC-like genes displayed distinct expression patterns in dorsal, lateral and ventral petals. It was found that VrCYC3 was located in nucleus. Further analysis showed that VrCYC3 had transcription activity and could interact with VrCYC1 and VrCYC2 in yeast cell. Moreover, the deletion of two amino acid residues in the R domain of VrCYC3 protein could decrease its interaction with VrCYC1 and VrCYC2 proteins. Our results suggest that LjCYC3/VrCYC3 orthologs play conserved roles determining the lateral petal shape and identity of zygomorphic flower as well as asymmetric flower in Papilionoideae.

SYMMETRIC PETALS 1 Encodes an ALOG Domain Protein that Controls Floral Organ Internal Asymmetry in Pea (Pisum sativum L.).

In contrast to typical radially symmetrical flowers, zygomorphic flowers, such as those produced by pea (Pisum sativum L.), have bilateral symmetry, manifesting dorsoventral (DV) and organ internal (IN) asymmetry. However, the molecular mechanism controlling IN asymmetry remains largely unclear. Here, we used a comparative mapping approach to clone SYMMETRIC PETALS 1 (SYP1), which encodes a key regulator of floral organ internal asymmetry. Phylogenetic analysis showed that SYP1 is an ortholog of Arabidopsis thaliana LIGHT-DEPENDENT SHORT HYPOCOTYL 3 (LSH3), an ALOG (Arabidopsis LSH1 and Oryza G1) family transcription factor. Genetic analysis and physical interaction assays showed that COCHLEATA (COCH, Arabidopsis BLADE-ON-PETIOLE ortholog), a known regulator of compound leaf and nodule identity in pea, is involved in organ internal asymmetry and interacts with SYP1. COCH and SYP1 had similar expression patterns and COCH and SYP1 target to the nucleus. Furthermore, our results suggested that COCH represses the 26S proteasome-mediated degradation of SYP1 and regulates its abundance. Our study suggested that the COCH-SYP1 module plays a pivotal role in floral organ internal asymmetry development in legumes.

Love on wings, a Dof family protein regulates floral vasculature in Vigna radiata.

BACKGROUND: The interaction among plants and their pollinators has been a major factor which enriched floral traits known as pollination syndromes and promoted the diversification of flowering plants. One of the bee-pollination syndromes in Faboideae with keel blossoms is the formation of a landing platform by wing and keel petals. However, the molecular mechanisms of elaborating a keel blossom remain unclear. RESULTS: By performing large scale mutagenesis, we isolated and characterized a mutant in Vigna radiata, love on wings (low), which shows developmental defects in petal asymmetry and vasculature, leading to a failure in landing platform formation. We cloned the locus through map-based cloning together with RNA-sequencing (RNA-seq) analysis. We found that LOW encoded a nucleus-localized Dof-like protein and was expressed in the flower provascular and vascular tissues. A single copy of LOW was detected in legumes, in contrast with other taxa where there seems to be at least 2 copies. Thirty one Dof proteins have been identified from the V. radiata's genome, which can be further divided into four Major Cluster of Orthologous Groups (MCOGs). We also showed that ectopic expression of LOW in Arabidopsis driven by its native promoter caused changes in petal vasculature pattern. CONCLUSIONS: To summarize, our study isolated a legume Dof-like factor LOW from V. radiata, which affects vasculature development in this species and this change can, in turn, impact petal development and overall morphology of keel blossom.

The CYCLOIDEA-RADIALIS module regulates petal shape and pigmentation, leading to bilateral corolla symmetry in Torenia fournieri (Linderniaceae).

The diverse pigmentation patterns of flower corollas probably result from pollinator-mediated selection. Previous studies demonstrated that R2R3-MYB factors may have been recruited in the regulation of corolla pigmentation. However, how R2R3-MYBs became so diverse in their regulation of different pigmentation patterns remains unclear. Here, we studied a Lamiales species, Torenia fournieri, which has elaborate zygomorphic flowers with dorsal-ventral asymmetries in corolla pigmentation. We found recent gene duplication events in CYCLOIDEA-like (CYC-like) and RADIALIS-like (RAD-like) genes, and functionally analyzed three dorsal-specific expression factors: TfCYC1, TfCYC2, and TfRAD1. We found that the CYC-RAD module coordinates petal shape and corolla pigmentation, as ectopic expression of TfCYC2 or TfRAD1 disrupted the asymmetric corolla pigmentation pattern and produced strongly dorsalized flowers. Dorsal petal identity was lost when TfCYC2 was down-regulated or when TfRAD1 was knocked out. In T. fournieri, the diversified CYC and RAD genes have evolved regulatory loops, and TfCYC2 binds directly to the regulatory regions of an R2R3-MYB factor gene, TfMYB1, which might lead to its asymmetric expression and ultimately establish the asymmetric pigmentation pattern. These findings support the existence of a regulatory module that integrates dorsal-ventral patterning and asymmetric corolla pigmentation in T. fournieri.