AUTHOR=Bicknell Ross , Gaillard Marion , Catanach Andrew , McGee Robert , Erasmuson Sylvia , Fulton Beatrice , Winefield Christopher 

TITLE=Genetic mapping of the LOSS OF PARTHENOGENESIS locus in Pilosella piloselloides and the evolution of apomixis in the Lactuceae

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1239191

DOI=10.3389/fpls.2023.1239191

ISSN=1664-462X

ABSTRACT=<p><italic>Pilosella piloselloides</italic> var. <italic>praealta</italic> (syn. <italic>P. praealta</italic>; <italic>Hieracium praealtum</italic>) is a versatile model used to study gametophytic apomixis. In this system apomixis is controlled by three loci: one that controls the avoidance of meiosis (<italic>LOA</italic>), one that controls the avoidance of fertilization (<italic>LOP</italic>) and a third that controls autonomous endosperm formation (<italic>AutE</italic>). Using a unique polyhaploid mapping approach the <italic>LOP</italic> locus was mapped to a 654 kb genomic interval syntenic to linkage group 8 of <italic>Lactuca sativa</italic>. Polyhaploids form through the gametophytic action of a dominant determinant at <italic>LOP</italic>, so the mapped region represents both a functional and a physical domain for <italic>LOP</italic> in <italic>P. piloselloides</italic>. Allele sequence divergence (ASD) analysis of the <italic>PARTHENOGENESIS</italic> (<italic>PAR)</italic> gene within the <italic>LOP</italic> locus revealed that dominant <italic>PAR</italic> alleles in <italic>Pilosella</italic> remain highly similar across the genus, whilst the recessive alleles are more divergent. A previous report noted that dominant <italic>PAR</italic> alleles in both <italic>Pilosella</italic> and <italic>Taraxacum</italic> are modified by the presence of a class II transposable element (TE) in the promoter of the gene. This observation was confirmed and further extended to the related genus <italic>Hieracium</italic>. Sufficient differences were noted in the structure and location of the TE elements to conclude that TE insertional events had occurred independently in the three genera. Measures of allele crossover amongst the polyhaploids revealed that <italic>P. piloselloides</italic> is an autopolyploid species with tetrasomic inheritance. It was also noted that the dominant determinant of <italic>LOP</italic> in <italic>P. piloselloides</italic> could transmit via a diploid gamete (pollen or egg) but not via a haploid gamete. Using this information, a model is presented of how gametophytic apomixis may have evolved in several members of the Lactuceae, a tribe of the Asteraceae.</p>