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.
The arabinogalactan protein (AGP) family is one of the most complex protein families and is ubiquitous in the plant kingdom. Moreover, it has been demonstrated to play various roles during plant reproduction. A typical AGP contains a hydroxyproline-rich core protein with high heterogeneity and varying numbers of polysaccharide side chains. However, the functions of the polysaccharide components (i.e. AG sugar chains) remain largely unknown due to the general difficulties associated with studying sugar chains in glycobiology. In recent years, methodological breakthroughs have resulted in substantial progress in AGP research. Here, we summarise the multiple roles of AGPs during plant gametophyte development and male-female communication, with a focus on recent advances. In addition, we discuss the analytical tools used in AGP research, and the biosynthesis and function of AG sugar chains. A comprehensive understanding of the AGP family will help clarify the mechanisms precisely controlling reproductive processes.
Flowers of honey plants (Torenia) face various abiotic stressors, including rain, that can damage pollens and dilute nectar. Many Torenia species are thought to have evolved a modified corolla base termed the corolla neck to prevent raindrops from contacting the nectar. Although this hypothesis was postulated long ago, direct validation is lacking. Here, we have evaluated Torenia fournieri, the corolla tube of which differentiates into distinct regions: a conical tube above that connects to an inflated base through a constriction. This constriction and inflated base are collectively referred to as the corolla neck. Using transcriptomic sequencing and genome-editing approaches, we have characterized an ALOG gene, TfALOG3, that is involved in formation of the corolla neck. TfALOG3 was found expressed in the epidermis of the corolla neck. Cells in the corolla bottom differentiated and expanded in wild-type T. fournieri, whereas such cells in TfALOG3 loss-of-function mutants failed to develop into a corolla neck. Water easily contacted the nectary in the absence of the corolla neck. Taken together, our study unveils a novel gene that controls corolla tube differentiation and demonstrates a hypothetical property of the corolla neck.
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.
Many studies suggest that there are distinct regulatory processes controlling compound leaf development in different clades of legumes. Loss of function of the LEAFY (LFY) orthologs results in a reduction of leaf complexity to different degrees in inverted repeat-lacking clade (IRLC) and non-IRLC species. To further understand the role of LFY orthologs and the molecular mechanism in compound leaf development in non-IRLC plants, we studied leaf development in unifoliate leaf (un) mutant, a classical mutant of mungbean (Vigna radiata L.), which showed a complete conversion of compound leaves into simple leaves. Our analysis revealed that UN encoded the mungbean LFY ortholog (VrLFY) and played a significant role in leaf development. In situ RNA hybridization results showed that STM-like KNOXI genes were expressed in compound leaf primordia in mungbean. Furthermore, increased leaflet number in heptafoliate leaflets1 (hel1) mutants was demonstrated to depend on the function of VrLFY and KNOXI genes in mungbean. Our results suggested that HEL1 is a key factor coordinating distinct processes in the control of compound leaf development in mungbean and its related non-IRLC legumes.
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