Abstract
The organogenesis and development of reproductive organs, i.e., stamen and gynoecium, are important floral characteristics that are closely related to pollinators and reproductive fitness. As a genus from Magnoliaceae, Liriodendron has only two relict species: L. chinense and L. tulipifera. Despite the similar flower shapes of these species, their natural seed-setting rates differ significantly, implying interspecies difference in floral organogenesis and development. MADS-box genes, which participate in floral organogenesis and development, remain unexplored in Liriodendron. Here, to explore the interspecies difference in floral organogenesis and development and identify MADS-box genes in Liriodendron, we examined the stamen and gynoecium primordia of the two Liriodendron species by scanning electron microscopy combined with paraffin sectioning, and then collected two types of primordia for RNA-seq. A total of 12 libraries were constructed and 42,268 genes were identified, including 35,269 reference genes and 6,999 new genes. Monoterpenoid biosynthesis was enriched in L. tulipifera. Genome-wide analysis of 32 MADS-box genes was conducted, including phylogenetic trees, exon/intron structures, and conserved motif distributions. Twenty-six genes were anchored on 17 scaffolds, and six new genes had no location information. The expression profiles of MIKC-type genes via RT-qPCR acrossing six stamen and gynoecium developmental stages indicates that the PI-like, AG/STK-like, SEP-like, and SVP-like genes may contribute to the species-specific differentiation of the organogenesis and development of reproductive organs in Liriodendron. Our findings laid the groundwork for the future exploration of the mechanism underlying on the interspecific differences in reproductive organ development and fitness in Liriodendron.
Highlights
The organogenesis and development of reproductive organs, i.e., stamen and gynoecium, are important floral characteristics that are closely related to pollinators and reproductive fitness
The shoot apical meristems of Liriodendron species develop into floral meristems less than two months after anthesis, and almost four months are required for the floral organ primordia to arise and differentiate
The reference genome was from L. chinense, while the RNA-seq samples came from L. chinense and L. tulipifera; we identified quite a large number of new genes that represented a good supplement to the L. chinense genome
Summary
The organogenesis and development of reproductive organs, i.e., stamen and gynoecium, are important floral characteristics that are closely related to pollinators and reproductive fitness. The early stages of reproductive organ organogenesis and development determine the floral structure These transitions are promoted by genes identified to encode transcription factors (TF)[12,13]. It is vital to study the early stages of reproductive organ organogenesis and development in Liriodendron species to explore the differences between L. chinense and L. tulipifera. MADS-box genes have been generally recognized to play important roles in floral organ differentiation, flowering time, and fruit development and ripening in a ngiosperms[15,16] These genes have a highly conserved MADS domain (for MCM1, AG, DEF and SRF) composed of approximately 55–60 amino acids and are divided into two categories, i.e., type I and type II, according to phylogenetic a nalysis[15,16]. Their functions and expression patterns are highly conserved in angiosperms
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