Phenotypically abnormal cotyledonary Vitis vinifera embryos differ in anatomy, endogenous hormone levels and transcriptome profiles

In many perennial fruit species, including grapevine (Vitis vinifera L.), the highly complex process of somatic embryogenesis (SE) can result in the formation of a deformed embryo, although the underlying reasons are still poorly understood. Here, V. vinifera cv. 'Chardonnay' cotyledonary embryos with distinct morphologies were used to address this issue. Normal cotyledonary embryos (NCEs) and elongated cotyledonary embryos (ECEs) were observed to have better-developed vasculature and shoot meristems than the vitrified cotyledonary embryos (VCEs) and fused cotyledonary embryos (FCEs), but ECEs were less developed. We determined that the morphological differences in these phenotypically abnormal embryos were likely associated with endogenous hormone levels, since concentrations of the phytohormones indoleacetic acid (IAA) and abscisic acid (ABA) in NCEs were higher than in the other three types. Comparative transcriptome analysis revealed large differences in gene expression of the hormone signaling pathways in normal and abnormal cotyledonary embryos. Weighted gene co-expression network analysis of the different cotyledonary types allowed the identification of co-regulated gene modules associated with SE, suggesting a role for ERF family genes and other transcription factors (TFs) in regulating morphology. Moreover, an analysis of morphology-specific gene expression indicated that the activation of a specific protein kinase, small heat shock proteins (sHSPs) and certain TFs was closely associated with the formation of normal cotyledonary embryos. Our comparative analyses provide insights into the gene networks regulating somatic cotyledon development and open new avenues for research into plant regeneration and functional genomic studies of malformed embryos.

Automated summary

In perennial fruit species, such as grapevine, the phenomenon of somatic embryogenesis (SE) can lead to the formation of deformed embryos, for reasons that are still not well understood. In this study, the authors investigated cotyledonary embryos of grapevine cv. 'Chardonnay' with distinct morphologies to explore this issue. They found that normal cotyledonary embryos (NCEs) and elongated cotyledonary embryos (ECEs) had better-developed vasculature and shoot meristems compared to vitrified cotyledonary embryos (VCEs) and fused cotyledonary embryos (FCEs), but ECEs were less developed. The authors suggested that the morphological differences in these abnormal embryos were likely associated with changes in endogenous hormone levels, particularly indoleacetic acid (IAA) and abscisic acid (ABA). Comparative transcriptome analysis revealed significant differences in gene expression related to hormone signaling pathways in normal and abnormal cotyledonary embryos. Weighted gene co-expression network analysis identified co-regulated gene modules associated with SE, indicating the involvement of ERF family genes and other transcription factors (TFs) in regulating embryonic morphology. Furthermore, the authors found that specific protein kinases, small heat shock proteins (sHSPs), and TFs were closely associated with the formation of normal cotyledonary embryos. This study provides valuable insights into the genetic networks controlling cotyledon development during somatic embryogenesis, opening up new avenues for research on plant regeneration and functional genomics of malformed embryos.