PN_ TGS1-like downregulation induces the formation of multiple non-reduced embryo sacs in ovules of sexual Paspalum notatum

SIENA LA; SOUZA CANADA ED; ORTIZ JPA; PERMINGEAT HR; COLONO CM; LEBLANC O; PESSINO SC

Congreso; ALAG 2019; 2019

Paspalum notatum is a perennial grass including sexual diploid and apomictic tetraploid cytotypes. The last ones produce maternal seeds by forming non-reduced (aposporous) embryo sacs in ovule nucella, followed by parthenogenetic embryo and pseudogamous endosperm generation. In P. notatum, the TRIMETHYLGUANOSINE SYNTHASE 1-LIKE gene (PN_TGS1-LIKE) is upregulated in ovules of sexual biotypes with respect to apomictic ones. Our objective was to study the role of this particular candidate in the sexuality-apomixis transition. Undifferentiated calli originated from sexual plants were transformed with a PN_TGS1-like antisense construction. Three of the antisense lines (2.9, 2.13, and 2.14) showed a 2-3 fold reduction of PN_TGS1-like expression at both leaves and flowers. PN_TGS1-like downregulation caused delayed flowering, the emergence of apospory initials around megaspore mother cells and the formation of multiple aposporous-like embryo sacs in 22-24 % of all ovules. Morever, antisense lines developed numerous trichomes on the adaxial surface of leaves. In contrast, the amount of viable pollen in transgenic and control plants was equivalent. Flow cytometry analysis of the scarce seed set (full seeds: 9-13%) revealed embryo:endosperm ploidy ratios corresponding to sexual reproductive events in all cases (100 total seeds). We concluded that PN_TGS1-like is an apospory repressor which must be down-regulated to allow the emergence of unreduced embryo sacs, yet it is not related with parthenogenesis or endosperm development.