Busted: maternal modifiers of the triploid block involved in seed size control

Abstract

ABSTRACTThe triploid block leads to seed abortion in crosses involving tetraploid Col-0 pollen. The genetic basis underlying this phenomenon is established in the endosperm and attributed to parental genomic imprinting. This research utilised the genetic variation in Arabidopsis to identify the genomic regions harbouring the maternal modifiers of the triploid block to produce viable large seeds. Distinct chromosomal regions were identified in Bla-1 and Tsu-0 accessions. The Bla-1 maternal modifier maps to theTTG2locus at the lower end of chromosome 2 to produce large viable seeds in response to a triploid block. Tsu-0 accession, on the other hand, recruits theTTG1locus on the upper arm of chromosome 5 as a maternal modifier of the triploid block.TTG1andTTG2mutations significantly increased the proportion of large viable seeds in interploidy crosses. Both genes are involved in transcriptional regulation in the flavonoid biosynthesis pathway. However, to regulate seed size in diploids,TTG1functions synergistically with auxin but does so independently ofTTG2. This work contributed to the genetic framework for theTTG1andTTG2seed size roles.HIGHLIGHTSDifferent Arabidopsis accessions recruit maternal modifiers to repress Col-killing in F1triploids.These maternal modifiers may operate in the same pathway, such as the flavonoid biosynthesis pathway or other interconnected pathways such as auxin.TTG1andTTG2generally increase F1triploid survival but in an accession-dependent manner.TTG1differentially exhibits a strong positive additive interaction with auxin to increase diploid seed size.TheTTG1/TTG2roles in diploid seed size control appear to have diverged somewhere in the auxin branch of the flavonoid biosynthesis pathway.