Comparative transcriptome analysis between somatic embryos (SEs) and zygotic embryos in cotton: evidence for stress response functions in SE development

Abstract

SummaryAs a product of asexual reproduction in plants, the somatic embryo (SE) differentiates into a new plantlet via a zygotic embryogenesis-like process. Here, we present the phenotypic and cellular differences between SEs and zygotic embryos (ZEs) revealed by histological section scanning using three parallel development stages of the two types of embryos of cotton (Gossypium hirsutum cv. YZ1), including globular, torpedo and cotyledonary-stages. To identify the molecular characteristics of SE development in cotton, the digital gene expression system was used to profile the genes active during SE and ZE development. A total of 4242 differentially expressed genes (DEGs) were identified in at least one developmental stage. Expression pattern and functional classification analysis based on these DEGs reveals that SE development exhibits a transcriptional activation of stress responses. RT-PCR analysis further confirmed enhanced expression levels of stress-related genes in SEs than in ZEs. Experimental stress treatment, induced by NaCl and ABA, accelerated SE development and increased the transcription of genes related to stress response, in parallel with decelerated proliferation of embryogenic calluses under stress treatment. Our data reveal that SE development involves the activation of stress responses, which we suggest may regulate the balance between cell proliferation and differentiation. These results provide new insight into the molecular mechanisms of SE development and suggest strategies that can be used for regulating the developmental processes of somatic embryogenesis.

Transcription Factors in the Regulation of Somatic Embryogenesis

“…In line with this postulate, various stress factors (osmotic, salt, water and heavy metals) were shown to replace or enhance the hormone treatment that was used for SE induction in different plant species (Kamada et al 1993;Patnaik et al 2005). Relevant to the assumed role of stress in SE induction, numerous (4-12 %) stress-related mRNAs have been found among those that were differentially expressed during SE induction (Legrand et al 2007;Chakrabarty et al 2010;Yang et al 2012;Jin et al 2014;Wickramasuriya and Dunwell 2015). In conjunction with the stress-regulated mechanism of SE induction, almost 40 % of the differentially expressed TF genes in an embryogenic culture of Arabidopsis were annotated to stress-related functions (Gliwicka et al 2013).…”

Somatic and zygotic embryos share common developmental features at the onset of plant embryogenesis

“…Phillips et al (1990) emphasized that alterations in DNA methylation in cultured cells are induced by general stress caused by tissue culture conditions and not specifically by auxin. Also, a number of methylation-related genes encoding proteins involved in chromatin silencing, DNA, RNA and protein/histone methylation are shown to be highly expressed during the course of both SE and ZE in cotton (Jin et al 2013).…”

“…Nowadays, microdissection techniques and molecular technology including microarray and next-generation sequencing have made it possible to compare molecular mechanisms regulating development of somatic and zygotic embryos in different plant species. Detailed comparative transcriptome analysis of somatic and zygotic cotton embryos reveals a set of embryogenesisspecific genes that are shared between somatic and zygotic embryogenesis, indicating molecular relatedness of the two types of embryogenesis (Jin et al 2013). These authors have made the first detailed comparative analysis of expressional changes during three stages (globular, torpedo and cotyledonary) of ZE and SE, demonstrating the power and advantages of a comparative approach for the elucidation of molecular mechanisms underlying plant embryogenesis.…”

Somatic Embryogenesis in Agave spp.

“…It is well known that diverse kinds of stresses and plant growth regulators play an important role in somatic embryogenesis. The utilization of 25 % MS medium and the addition of 60 g L −1 sucrose in the induction process could have acted positively as starvation and osmotic stresses, respectively, as it has been demonstrated in other plant species (Jin et al 2014). …”

“…Early somatic embryogenesis stages resemble those of zygotic embryogenesis, and many phenotypic and molecular features are shared between both types of embryogenesis (Jin et al 2014). In A. tequilana, the rare occurrence of dicotyledonar zygotic embryos was recently reported (Ayala-González et al 2014).…”