Abstract
BackgroundMaize is one of the primary crops of genetic manipulation, which provides an excellent means of promoting stress resistance and increasing yield. However, the differences in induction and regeneration capacity of embryonic callus (EC) among various genotypes result in genotypic dependence in genetic transformation.ResultsIn this study, embryonic calli of two maize inbred lines with strong redifferentiation capacity and two lines with weak redifferentiation capability were separately subjected to transcriptome sequencing analysis during the early redifferentiation stages (stage I, 1–3 d; stage II, 4–6 d; stage III, 7–9 d) along with their corresponding controls. A total of ~ 654.72 million cDNA clean reads were yielded, and 62.64%~ 69.21% clean reads were mapped to the reference genome for each library. In comparison with the control, the numbers of differentially expressed genes (DEGs) for the four inbred lines identified in the three stages ranged from 1694 to 7193. By analyzing the common and specific DEGs of the four materials, we found that there were 321 upregulated genes and 386 downregulated genes identified in the high-regeneration lines (141 and DH40), whereas 611 upregulated genes and 500 downregulated genes were specifically expressed in the low-regeneration lines (ZYDH381–1 and DH3732). Analysis of the DEG expression patterns indicated a sharp change at stage I in both the high- and low-regeneration lines, which suggested that stage I constitutes a crucial period for EC regeneration. Notably, the specific common DEGs of 141 and DH40 were mainly associated with photosynthesis, porphyrin and chlorophyll metabolism, ribosomes, and plant hormone signal transduction. In contrast, the DEGs in ZYDH381–1 and DH3732 were mainly related to taurine and hypotaurine metabolism, nitrogen metabolism, fatty acid elongation, starch and sucrose metabolism, phenylpropanoid biosynthesis, and plant circadian rhythm. More importantly, WOX genes, which have an ancestral role in embryo development in seed plants and promote the regeneration of transformed calli, were specifically upregulated in the two high-regeneration lines.ConclusionsOur research contributes to the elucidation of molecular regulation during early redifferentiation in the maize embryonic callus.
Highlights
Maize is one of the primary crops of genetic manipulation, which provides an excellent means of promoting stress resistance and increasing yield
The Callus differentiating rate (CDR) and Callus plantlet number (CPN) of inbred lines 141 and DH40 were much higher than DH3732 and ZYDH381–1 (Fig. 1a) [85]
For the low-regeneration materials (DH3732 and ZYDH381–1), only some calli became green after 6 d, and no adventitious bud formation was observed during the whole process (Fig. 1b)
Summary
Maize is one of the primary crops of genetic manipulation, which provides an excellent means of promoting stress resistance and increasing yield. Genetic transformation is presently widely used to improve yield and stress resistance and for gene function validation in maize, which largely depend on callus induction and regeneration from maize immature embryos [1,2,3]. Armstrong et al [1] classified maize calli into three types, namely, I-, II -, and III-type calli, based on the callus characteristics. Among these types, only the II-type callus, known as embryonic callus, has cell totipotency and the ability to regenerate into whole plants and is widely applied to genetic transformation in maize. Research on quantitative trait locus (QTL) mapping revealed that the regenerative capability of the embryonic callus is controlled by multiple genes in maize [8, 86]
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