The MAP3K-Coding QUI-GON JINN (QGJ) Gene Is Essential to the Formation of Unreduced Embryo Sacs in Paspalum.

Micaela Mancini,Juan Pablo A Ortiz,Fulvio Pupilli,Ana María González,Olivier Leblanc,Carolina Colono,Diva Maria De Alencar Dusi,Silvina C Pessino,Hugo Permingeat,Vera Tavares De Campos Carneiro,Maricel Podio,Lorena Siena,José Guillermo Seijo,Silvina A Felitti,Celeste Azzaro

doi:10.3389/fpls.2018.01547

Abstract

Apomixis is a clonal mode of reproduction via seeds, which results from the failure of meiosis and fertilization in the sexual female reproductive pathway. In previous transcriptomic surveys, we identified a mitogen-activated protein kinase kinase kinase (N46) displaying differential representation in florets of sexual and apomictic Paspalum notatum genotypes. Here, we retrieved and characterized the N46 full cDNA sequence from sexual and apomictic floral transcriptomes. Phylogenetic analyses showed that N46 was a member of the YODA family, which was re-named QUI-GON JINN (QGJ). Differential expression in florets of sexual and apomictic plants was confirmed by qPCR. In situ hybridization experiments revealed expression in the nucellus of aposporous plants’ ovules, which was absent in sexual plants. RNAi inhibition of QGJ expression in two apomictic genotypes resulted in significantly reduced rates of aposporous embryo sac formation, with respect to the level detected in wild type aposporous plants and transformation controls. The QGJ locus segregated independently of apospory. However, a probe derived from a related long non-coding RNA sequence (PN_LNC_QGJ) revealed RFLP bands cosegregating with the Paspalum apospory-controlling region (ACR). PN_LNC_QGJ is expressed in florets of apomictic plants only. Our results indicate that the activity of QGJ in the nucellus of apomictic plants is necessary to form non-reduced embryo sacs and that a long non-coding sequence with regulatory potential is similar to sequences located within the ACR.

Highlights

Asexual reproduction can naturally occur in ovules of several flowering plant taxa through apomixis, an alternative route to sexuality, which allows the formation of maternal embryos within seeds (Nogler, 1984; Carman, 1997)
Laspina et al (2008) reported similarity between a mRNA fragment differentially expressed in florets of sexual and apomictic P. notatum plants (N46) and a full-length cDNA transcribed from the maize gene GRMZM6G513881, which encodes a MAP3K protein
QPCR of cDNAs originated from a mix of flowers at different developmental stages with primers located inside the intron revealed no significant differential representation between reproductive modes

Summary

Introduction

Asexual reproduction can naturally occur in ovules of several flowering plant taxa through apomixis, an alternative route to sexuality, which allows the formation of maternal embryos within seeds (Nogler, 1984; Carman, 1997). This atypical trait relies on developmental alterations which cause unreduced cells within the ovule to acquire a reproductive fate. Apomictic pathways are usually classified into two major classes (i.e., sporophytic and gametophytic), depending on the origin of maternal embryos (Hand and Koltunow, 2014). In all gametophytic apomicts the embryo develops autonomously, while the formation of the endosperm can be either autonomous or fertilization-dependent (pseudogamous) (Bicknell and Koltunow, 2004)

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Conclusion