Temporal Expression Patterns of Hormone Metabolism Genes during Imbibition of Arabidopsis thaliana Seeds: A Comparative Study on Dormant and Non-Dormant Accessions

Seed imbibition is a prerequisite for subsequent dormancy and germination control. Here, we investigated imbibition responses of Arabidopsis seeds by transcriptomic and hormone profile analyses using dormant [Cape Verde Islands (Cvi)] and non-dormant [Columbia (Col)] accessions. Once imbibed, seeds of both accessions swelled most up to 3h, reflecting water uptake. Microarray analysis showed that in both accessions, seeds imbibed for 15min, 30min and 1h were less active in gene expression than at 3h. More than 2,000 genes were either up-regulated or down-regulated in seeds imbibed for 3h. Some genes up-regulated at 3h were already induced in seeds imbibed for 1h, suggestive of genome reprogramming early after the onset of imbibition. Imbibition-induced genes in seeds imbibed for 3h included those up-regulated in both Col and Cvi (common) or unique to either accession (accession specific). Up-regulated genes that were both common and Cvi-specific were over-represented for sugar metabolism and the pentose phosphate pathway, whereas Col-specific genes were over-represented for ribosomal protein genes. Quantification of plant hormones showed that ABA and salicylic acid (SA) contents were higher, but gibberellin A(4) (GA(4)), N-6-((2)-isopentenyl)adenine (iP), jasmonic acid (JA), JAisoleucine (JA-Ile) and IAA were lower in imbibed seeds of Cvi compared with Col. In addition, changes in IAA and JA were initiated before 1h, whereas ABA and JA-Ile declined 3h after the onset of imbibition. An increase in GA(4) and iP appeared to be correlated temporally with the initiation of secondary water uptake, which marks the completion of germination.