High expression of SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE coincides with initiation of various developmental pathways in in vitro culture of Trifolium nigrescens.

Maria Pilarska,Robert Konieczny,Filip Bartnicki,Jan Salaj,Przemysław Malec

doi:10.1007/s00709-015-0814-5

Abstract

The aim of this study was to identify and examine the expression pattern of the ortholog of SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE gene from Trifolium nigrescens (TnSERK) in embryogenic and non-regenerative cultures of immature cotyledonary-stage zygotic embryos (CsZEs). In the presence of 1-naphthaleneacetic acid and N6-[2-isopentenyl]-adenine, the CsZE regenerated embryoids directly and in a lengthy culture produced callus which was embryogenic or remained non-regenerative. As revealed by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), the TnSERK was expressed in both embryogenic and non-regenerative cultures, but the expression level was significantly higher in embryogenic ones. An in situ RNA hybridization assay revealed that the expression of TnSERK preceded the induction of cell division in explants, and then, it was maintained exclusively in actively dividing cells from which embryoids, embryo-like structures (ELSs), callus or tracheary elements were produced. However, the cells involved in different morphogenic events differed in intensity of hybridization signal which was the highest in embryogenic cells. The TnSERK was up-regulated during the development of embryoids, but in cotyledonary embryos, it was preferentially expressed in the regions of the apical meristems. The occurrence of morphological and anatomical abnormalities in embryoid development was preceded by a decline in TnSERK expression, and this coincided with the parenchymatization of the ground tissue in developing ELSs. TnSERK was also down-regulated during the maturation of parenchyma and xylem elements in CsZE and callus. Altogether, these data suggest the involvement of TnSERK in the induction of various developmental programs related to differentiation/transdifferentiation and totipotent state of cell(s).Electronic supplementary materialThe online version of this article (doi:10.1007/s00709-015-0814-5) contains supplementary material, which is available to authorized users.

Highlights

Somatic embryogenesis (SE) is a process whereby a single plant cell or group of cells from somatic tissue forms an embryo
Extensive research has been carried out on genes with a specific role in the induction and maintenance of SE. One of such genes is SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1 (SERK1) which encodes a transmembrane protein kinase belonging to the family of leucinerich repeat protein receptor-like kinases (Hecht et al 2001)
In Arabidopsis thaliana, five genes belonging to the SERK family were identified and overexpression of SERK1 was reported to lead to a significant increase in embryogenic competence in transgenic lines (Hecht et al 2001)

Summary

Introduction

Somatic embryogenesis (SE) is a process whereby a single plant cell or group of cells from somatic tissue forms an embryo. Extensive research has been carried out on genes with a specific role in the induction and maintenance of SE (for a review, see Ikeda et al 2006; Elhiti et al 2013) One of such genes is SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1 (SERK1) which encodes a transmembrane protein kinase belonging to the family of leucinerich repeat protein receptor-like kinases (Hecht et al 2001). Recent studies showed that AtSERK proteins play a crucial role in brassinosteroid signaling as co-receptors of BRASSINOSTEROID-INSENSITIVE1 (BRI1) (Albrecht et al 2008; Gou et al 2012) This multifunctionality of SERKs implies a need for a detailed expressional analysis of each new identified gene to properly determine its possible function in the biology of a particular plant

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