Auxin response repressor IAA16 defective mutants show developmental alterations in female gametophytes and embryos in Arabidopsis thaliana

MS VEGA; LEBLANC O; PESSINO SC; ORTIZ JPA; SIENA LA

Rosario

Congreso; IV International Congress on Apomixis; 2023

Grupo DREP-IICAR-CONICET

Auxin plays an essential role in many aspects of plant development, including growth and reproduction. Recently, we have found that the auxin response repressor IAA30 of Paspalum notatum is down-regulated in ovules of apomictic genotypes compared to sexual genotypes at the stages of anthesis and early embryogenesis. Furthermore, its expression level is negatively correlated with apospory expressivity in facultative apomicts, and differences in spatio-temporal expression between reproductive mode were revealed by in situ hybridization experiments. These results suggest a contrasting regulation of auxin signalling during sexual and apomictic seed formation in the species. To analyze the biological function of IAA30 during plant reproduction and investigate its possible association with the apomictic phenotype, we started the functional characterization of IAA16, its orthologue in Arabidopsis thaliana. RT-PCR experiments showed that IAA16 is expressed in siliques, leaves, seedlings and roots. Cytoembryological analyses of two iaa16 mutant lines revealed formation of multiple enlarged cells around the megaspore mother cell, the functional megaspore and the embryo sac, an observation reminiscent of apospory initials. After pollination, both lines showed defects in embryo patterning and occurrence of twin embryos. We crossed iaa16 with a line carrying the pWOX2-CENH3- GFP reporter construct. Analysis of double homozygous F2 plants confirmed the abnormal symmetry patterns detected in the embryos. Only 5-6% of the mutant seeds germinated onto MS germination medium produced normal seedlings, compared to 28% in Col-0. Four mutant seedlings with one cotyledon and two seeds with double shoots (polyembryony) were also detected. The results of this work indicate an essential role of IAA16 in the specification of the female germline fate and embryogenesis in Arabidopsis.