Abstract
BackgroundMost plants rely on photosynthesis; therefore, albinism in plants with leaves that are white instead of green causes slow growth, dwarfing, and even death. Although albinism has been characterized in annual model plants, little is known about albino trees. Jackfruit (Artocarpus heterophyllus) is an important tropical fruit tree species. To gain insight into the mechanisms underlying the differential growth and development between albino jackfruit mutants and green seedlings, we analyzed root, stem, and leaf tissues by combining PacBio single-molecule real-time (SMRT) sequencing, high-throughput RNA-sequencing (RNA-seq), and metabolomic analysis.ResultsWe identified 8,202 differentially expressed genes (DEGs), including 225 genes encoding transcription factors (TFs), from 82,572 full-length transcripts. We also identified 298 significantly changed metabolites (SCMs) in albino A. heterophyllus seedlings from a set of 692 metabolites in A. heterophyllus seedlings. Pathway analysis revealed that these DEGs were highly enriched in metabolic pathways such as ‘photosynthesis’, ‘carbon fixation in photosynthetic organisms’, ‘glycolysis/gluconeogenesis’, and ‘TCA cycle’. Analysis of the metabolites revealed 76 SCMs associated with metabolic pathways in the albino mutants, including L-aspartic acid, citric acid, succinic acid, and fumaric acid. We selected 225 differentially expressed TF genes, 333 differentially expressed metabolic pathway genes, and 76 SCMs to construct two correlation networks. Analysis of the TF–DEG network suggested that basic helix-loop-helix (bHLH) and MYB-related TFs regulate the expression of genes involved in carbon fixation and energy metabolism to affect light responses or photomorphogenesis and normal growth. Further analysis of the DEG–SCM correlation network and the photosynthetic carbon fixation pathway suggested that NAD-ME2 (encoding a malic enzyme) and L-aspartic acid jointly inhibit carbon fixation in the albino mutants, resulting in reduced photosynthetic efficiency and inhibited plant growth.ConclusionsOur preliminarily screening identified candidate genes and metabolites specifically affected in albino A. heterophyllus seedlings, laying the foundation for further study of the regulatory mechanism of carbon fixation during photosynthesis and energy metabolism. In addition, our findings elucidate the way genes and metabolites respond in albino trees.
Highlights
Most plants rely on photosynthesis; albinism in plants with leaves that are white instead of green causes slow growth, dwarfing, and even death
Our preliminarily screening identified candidate genes and metabolites affected in albino A. heterophyllus seedlings, laying the foundation for further study of the regulatory mechanism of carbon fixation during photosynthesis and energy metabolism
Analysis of transcriptome data To reveal the changes in gene expression in albino A. heterophyllus seedlings compared with green seedlings, we sequenced RNA pools from these seedlings and analyzed them using the PacBio Sequel platform
Summary
Most plants rely on photosynthesis; albinism in plants with leaves that are white instead of green causes slow growth, dwarfing, and even death. The significantly changed genes and metabolites were enriched in photosynthesis and starch and sucrose metabolic pathways after plant albinism [1]. In albino leaf tissue of Hydrangea macrophylla, combined metabolome and transcriptome analyses revealed the changed genes and metabolites were significantly enriched in the chlorophyll synthesis pathway and TCA cycle in response to albinism [2]. Yu et al obtained albino lethal mutants of A. thaliana at the seedling stage by knocking out the AtECB2 gene [5]. These findings indicate that albinism affects photosynthesis and energy metabolism, thereby hindering plant growth and development. Studies of albinism in tropical woody plants are lacking
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