A Plant-Specific TGS1 Homolog Influences Gametophyte Development in Sexual Tetraploid Paspalum notatum Ovules

ORTIZ, JUAN PABLO A.; SIENA, LORENA A.; ESPINOZA, FRANCISCO; COLONO, CAROLINA; SOUZA CANADA, EDUARDO DANIEL; GALDEANO, FLORENCIA; PESSINO, SILVINA C.; PERMINGEAT, HUGO R.; SPOTO, NICOLÁS; LEBLANC, OLIVIER

Frontiers in Plant Science

Frontiers

Año: 2019 vol. 10 p. 1 - 14

1664-462X

Aposporous apomictic plants form clonal maternal seeds by inducing the emergence ofnon-reduced (2n) embryo sacs in the ovule nucellus and the development of embryos byparthenogenesis. In previous work, we reported a plant-specific TRIMETHYLGUANOSINESYNTHASE 1 (TGS1) gene (PN_TGS1-like) showing expression levels positivelycorrelated with sexuality rates in facultative apomictic Paspalum notatum. PN_ TGS1-likedisplayed contrasting in situ hybridization patterns in apomictic and sexual plant ovulesfrom premeiosis to anthesis. Here we transformed sexual P. notatum with a TGS1-likeantisense construction under a constitutive promoter, in order to produce lines withreduced transcript representation. Antisense plants developed prominent trichomes onthe adaxial leaf surface, a trait absent from control genotypes. Reproductive developmentanalysis revealed occasional formation of twin ovules. While control individuals typicallydisplayed a single meiotic embryo sac per ovule, antisense lines showed 12.93?15.79%of ovules bearing extra nuclei, which can be assigned to aposporous-like embryo sacs(AES-like) or, alternatively, to gametophytes with a misguided cell fate development.Moreover, around 8.42?9.52% of ovules showed what looked like a combination ofmeiotic and aposporous-like sacs. Besides, 32.5% of ovules at early developmentalstages displayed nucellar cells with prominent nuclei resembling apospory initials (AIs),which surrounded the megaspore mother cell (MMC) or the MMC-derived meioticproducts. Two or more concurrent meiosis events were never detected, which suggest anon-reduced nature for the extra nuclei observed in the mature ovules, unless they weregenerated by proliferation and misguided differentiation of the legitimate meiotic products.The antisense lines produced a similar amount of viable even-sized pollen with respect tocontrol genotypes, and formed an equivalent full seed set (~9% of total seeds) after selfpollination. Flow cytometry analyses of caryopses derived from antisense lines revealedthat all full seeds had originated from meiotic embryo sacs (i.e. by sexuality). A reductionof 25.55% in the germination percentage was detected when comparing antisense lineswith controls. Our results indicate that PN_ TGS1-like influences ovule, gametophyte andpossibly embryo development.