Tetratricopeptide Repeat 2 Is a Quantitative Trait Locus that Acts Maternally to Control Seed Size and Regulate Carbohydrate Accumulation in Arabidopsis Seeds

Regulation of seed size is an important trait ecologically, evolutionarily, and agronomically. The Arabidopsis thaliana Seed Size QTL 1 (SSQ1) locus regulates a 10-15% change in seed size. We report here that the causal gene for this locus is Tetratricopeptide Repeat Protein 2 (TPR2), which encodes a co-chaperone involved in Hsp90/Hsp70 machinery. Loss-of-function of TPR2 produced significantly smaller seeds and overexpression led to significantly larger seeds than Col-0 wild type plants. These effects were replicated in Sha and Tsu-1 genetic backgrounds. Reciprocal genetic crosses indicate that this locus acts maternally. To elucidate how TPR2 regulates seed size, biomass composition in seeds were measured. While oil content remained unchanged, sucrose levels were markedly elevated in TPR2 overexpression lines, but reduced in tpr2 mutants, suggesting a role for TPR2 in modulating carbohydrate metabolism. Interestingly, heterologous expression of TPR2 across genetic backgrounds increased seed protein accumulation by 18% on average. These results indicate that TPR2 alters sugar metabolism and positively regulates protein abundance during Arabidopsis seed development.