Usefulness and Molecular Mechanism of Seed-Specificity Introduced by AtBZR1 and AtBES1 to Improve Seed Yield and Quality in Arabidopsis thaliana

This study generated the transgenic Arabidopsis lines pAt5g54000-AtBZR1::Col-0 and pAt5g54000-AtBES1::Col-0 , in which Arabidopsis BZR1 and BES1 ( AtBZR1 and AtBES1 ) were seed-specifically expressed with pAt5g54000 , a seed-specific promoter. Semi-quantitative RT-PCR and GUS -staining analysis demonstrated that the inserted AtBZR1 and AtBES1 were concentrated in seeds in siliques of transgenic plants. Seed number, length, width, and mass increased in the pAt5g54000-AtBZR1::Col-0 and pAt5g54000-AtBES1::Col-0 mutants compared to untransformed Arabidopsis . The endogenous levels of primary metabolites, such as carbohydrates, proteins, and lipids, in transgenic seeds were also higher than those in wild-type seeds, indicating that both seed size and quality are improved by seed-specific expression of AtBZR1 and AtBES1 in Arabidopsis . In both transgenic Arabidopsis seeds , relative to wild-type seeds, the expression of positive regulatory genes involved in determining seed size, such as SHORT HYPOCOTYL UNDER BLUE1 ( AtSHB1 ), MINISEED3 ( AtMINI3 ), and HAIKU2 ( AtIKU2 ), was increased by up-regulation of AtBZR 1 and AtBES1 as well as down-regulation of ABA Deficient 2 ( AtABA2 ) and ABA Insensitive 5 ( AtABI5 ). This result suggests that AtBZR1- and AtBES1-mediated signaling pathways such as AtBZR1/AtBES1 → AtSHB1 → AtMINI3 → AtIKU2 and AtBZR1/AtBES1 → AtABA2 , and/or AtABI5 → AtSHB1 → AtMINI3 → AtIKU2 increase the yield and quality of seeds in transgenic Arabidopsis . Taken together, our findings demonstrated the usefulness and applicability of seed-specific introduction of AtBZR1 and AtBES1 encoding key transcription factors in brassinosteroid signaling to improve seed yield and quality in Arabidopsis .