Abstract
To improve our understanding of the mechanism of maize seed germination under deep sowing, transcriptome sequencing and physiological metabolism analyses were performed using B73 embryos separated from ungerminated seeds (UG) or seeds germinated for 2 d at a depth of 2 cm (normal sowing, NS) or 20 cm (deep sowing, DS). Gene ontology (GO) analysis indicated that “response to oxidative stress” and “monolayer-surrounded lipid storage body” were the most significant GO terms in up- and down-regulated differentially expressed genes (DEGs) of DS. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis suggested that “phenylpropanoid biosynthesis” and “starch and sucrose metabolism” were critical processes in maize seed germination under deep-sowing conditions. Consistent with DEGs, the activities of superoxide dismutase, catalase, peroxidases and α-amylase, as well as the contents of gibberellin 4, indole acetic acid, zeatin and abscisic acid were significantly increased, while the jasmonic-acid level was dramatically reduced under deep-sowing stress. The expressions of six candidate genes were more significantly upregulated in B73 (deep-sowing-tolerant) than in Mo17 (deep-sowing-sensitive) at 20 cm sowing depth. These findings enrich our knowledge of the key biochemical pathways and genes regulating maize seed germination under deep-sowing conditions, which may help in the breeding of varieties tolerant to deep sowing.
Highlights
Maize (Zea mays L.) has the largest cultivation area and yield of all crops worldwide
ABA content in embryos of DS was 5.29 times and 5.60 times higher than that of ungerminated seeds (UG) and NS, respectively (Figure 7d). These results indicated that endogenous phytohormone GA4, IAA, zeatin and ABA may play positive roles in maize seed germination in response to deep sowing, while JA negatively regulated seed germination under deep-sowing conditions
In order to reveal the molecular mechanism of maize seed germination under deepsowing conditions, we mainly focused on differentially expressed genes (DEGs) that were only detected under deep-sowing conditions, i.e., the 134 upregulated and 47 downregulated DEGs
Summary
Maize (Zea mays L.) has the largest cultivation area and yield of all crops worldwide (http://faostat.fao.org/, 21 December 2021). 2/3 of maize-cultivated land is located in arid and semi-arid regions, where drought is the main environmental stress factor affecting production [2,3]. Deep sowing is an effective strategy to overcome drought stress because seeds can absorb water from deeper soil layers to germinate normally [4]. Deep-sowing-tolerant varieties reduce the sowing-failure risk caused by drought stress during seed germination in water-scarce environments. Existing varieties show poor germination ability when seeds are sown into deeper soil layers [5]. It is critical to develop deep-sowing-tolerant maize varieties for arid and semi-arid regions. The genetic mechanisms and regulatory genes related to deep-sowing germination ability remain a subject of limited understanding and exploration
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