Abstract
BackgroundPeanut zygotes typically divide a few times to form a pre-embryo before further embryonic development halts under normal day/night photoperiods. Ovary elongation, however, continuesforming a downward growing peg-like structure. When the peg is buried in the soil, embryo development resumes in the darkness. The embryo-located region (ER) of the peg begins to enlarge and form a pod, while the basal region (BR) of the peg has a distinct fate. The molecular mechanisms governing these unique embryo development processes are unknown.ResultsIn this study, histological analysis demonstrated that from 4 days after pollination to 3 days after soil penetration, the peanut pre-embryo remained morphologically similar. By 9 days after soil penetration, the embryo had changed to a globular embryo. Transcriptome analysis revealed differentially expressed genes in the ER and BR before and after peg soil penetration. In addition to light signaling and plant hormone metabolism genes, we identified differentially expressed genes in the ER that contribute to embryo development and pod formation processes, including MADS-box transcription factors, xyloglucan endotransglucosylase/hydrolase protein, cellulose synthase, homeobox-leucine zipper (HD-Zip) protein family genes, amino acid permease, and seed growth and embryo morphogenesis regulators (DA1, TCP3, and YABBY).ConclusionsA large number of genes were found to be differentially expressed in the ER and BR across three developmental peg stages. Exact changes in gene expression were also identified in the ER during early embryo and pod development. This information provides an expanded knowledgebase for understanding the mechanisms of early peanut pod formation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2857-1) contains supplementary material, which is available to authorized users.
Highlights
Peanut zygotes typically divide a few times to form a pre-embryo before further embryonic development halts under normal day/night photoperiods
We investigated gene expression in pegs of three developmental stages: (1) green or purple aerial-grown pegs (Stage 1, S1); (2) white pegs that had been buried in the soil for approximately 3 days and in which pod enlargement was not detected (Stage 2, S2); (3) pegs that had been buried in the soil for approximately 9 days and in which pod enlargement had been initiated (Stage 3, S3) [21]
Observation of early peanut embryo development Previous studies indicated that peanut zygotes divide only a few times after fertilization before the developmental process of the embryo ceases
Summary
Peanut zygotes typically divide a few times to form a pre-embryo before further embryonic development halts under normal day/night photoperiods. Ovary elongation continues due to the activity of an intercalary meristem just behind the pre-embryo [1]. The intercalary meristem of the peg is the site of cell division and is responsible for the elongation of the peg It is responsible for sensing and responding to gravity, light, and mechanical stimuli [4,5,6]. Elongation and downward growth of the peg ceases During this process, the ovary experiences a significant change in environmental conditions, including light signals, mechanical stimuli, moisture, and nutrition [7]. Should the peg fail to penetrate the soil, the normal day/night conditions aboveground inhibit completion of embryo and pod development. The downstream phytochrome signaling pathway involved in this biological process remains unclear
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