Abstract
The low ratio of embryonic callus (EC) induction has inhibited the rapid development of maize genetic engineering. Still, little is known to explain the genotype-dependence of EC induction. Here, we performed a large-scale, quantitative analysis of the maize EC metabolome and proteome at three typical induction stages in two inbred lines with a range of EC induction capabilities. Comparison of the metabolomes and proteomes suggests that the differential molecular responses begin at an early stage of development and continue throughout the process of EC formation. The two inbred lines show different responses under various conditions, such as metal ion binding, cell enlargement, stem cell formation, meristematic activity maintenance, somatic embryogenesis, cell wall synthesis, and hormone signal transduction. Furthermore, the differences in hormone (auxin, cytokinin, gibberellin, salicylic acid, jasmonic acid, brassinosteroid and ethylene) synthesis and transduction ability could partially explain the higher EC induction ratio in the inbred line 18-599R. During EC formation, repression of the “histone deacetylase 2 and ERF transcription factors” complex in 18-599R activated the expression of downstream genes, which further promoted EC induction. Together, our data provide new insights into the molecular regulatory mechanism responsible for efficient EC induction in maize.
Highlights
All plants possess the capacity of cellular totipotency, as single cells or tissues can regenerate into whole plants through somatic embryogenesis in response to certain stimuli[1], such as wounding or hormones
To better understand the metabolite differences during embryonic callus (EC) formation, total metabolites of control (C), stage I, stage II and stage III were extracted from calli induced for 0 d, 1–5 d, 6–10 d and 11–15 d, respectively
They were submitted to untargeted high performance liquid chromatography-mass spectrometry (HPLC-MS, biologically replicated six times) analysis
Summary
All plants possess the capacity of cellular totipotency, as single cells or tissues can regenerate into whole plants through somatic embryogenesis in response to certain stimuli[1], such as wounding or hormones. Two studies have reported proteomic changes during EC formation[9] and somatic embryogenesis[10]. They both used two-dimensional electrophoresis (2-DE) combined with mass spectrometry methods, which have several deficiencies: low protein identification ratios, difficulties in quantifying differentially expressed proteins and low reproducibility[11]. To account for the genotype dependence of EC induction rates[12], this study combined iTRAQ-based quantitative proteomics and liquid chromatography mass spectrometry (LC-MS) detected metabolomics to reveal the dynamic and complex network of maize EC formation using the 18-599R inbred line (with a strong capacity of EC formation) and the B73 inbred line (with a low capacity of EC formation)
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