Structure and expression analyses of the Fertilization Independent Seed (FIS) gene orthologs of the apomict Boechera species

Abstract

In this study Arabidopsis thaliana Fertilization Independent Seed 2 (FIS2) and Fertilization Independent Endosperm (FIE) genes orthologs were analysed in pseudogamous apomict and sexual Boechera species. FIS genes encode Polycomb Group (PcG) proteins that form a complex. Some mutant alleles of these genes produce endosperm like structure even in the absence of fertilization in A. thaliana. Therefore, the function of FIS complex known as to represses endosperm development prior to fertilization and plays an important role in regulating the endosperm development following fertilization. However, little is known about how apomicts have develop embryo without fertilization and adjusted endosperm development to cope with parental genome imbalance that results from non-reduction of maternal gametes. Therefore, the sexual and apomict Boechera species, as a close relative of A. thaliana, provide an attractive opportunity to investigate FIS function in pseudogamous apomicts. In this study, we report the full length genomic sequences of the apomict B. holboellii FIS2 and FIE through the mapping of the B. holboellii short-paired reads library, by using A. thaliana FIS genes as the reference sequences. We also obtained the genomic sequences of FIS2 and FIE from the sexual species B. stricta sequenced genome using the Phytozome 10.2. Then, we used these sequences to design primers and cDNAs were amplified by Reverse Transcriptase PCR. Full length cDNA of Boechera FIE transcript was 1110 bp and share 99% sequence similarity with AtFIE. Boechera FIS2 was 2188 bp and have 83% similarity with AtFIS2. The multiple alignment and phylogenetic analyses suggested that while FIE are highly conserved among Brassicacea, FIS2 is variable and also diverged from A. thaliana. In addition to sequence analyses we also investigated expression of FIE and FIS2 transcript in various tissues and they were observed in all tissues tested. These results indicated that FIE and FIS2 genes may play a role in the regulation of endosperm development in pseudogamous apomicts with diverse way from sexual relatives.