Plant hormones determine the differentiation of callus tissue during tissue culture of mature and immature Brachypodium distachyon embryos

Abstract Brachypodium distachyon has emerged as a new model for the structural and functional genomics of temperate grasses. Somatic embryo culture serves as an effective method for the genetic transformation of B. distachyon. However, the role of regulatory genes in inducing somatic embryogenesis through endogenous hormone modulation in B. distachyon remains unexplored. This study investigated the endogenous hormone levels and transcriptome data of embryogenic calli (EC) derived from both mature and immature B. distachyon embryos. Our findings indicate that higher levels of IAA and GAs promote the formation of mature embryo-produced compact embryogenic calli (MEC), whereas higher tZR and lower ABA levels promote the development of immature embryo-produced compact embryogenic calli (IEC). The differential expression of genes involved in the biosynthesis and signal transduction of auxin (YUCCA,ALDH, AUX/IAA), trans-zeatin riboside (CKX), gibberellin (KAO, GA3ox), and abscisic acid (AAO3, SnRK2) influences the endogenous hormone concentrations in MEC and IEC of B. distachyon. Specifically, increased expression of AUX/IAA is linked to MEC formation. Thus, the differential expression of genes associated with the AUX, CK, GA, and ABA biosynthesis and signal transduction pathways may modulate endogenous hormone levels, steering the differentiation of MEC and IEC in B. distachyon. Keywords Brachypodium distachyon·embryogenic calli· differentially expressed genes·endogenous hormone