Overexpression of AtAHL20 causes delayed flowering in Arabidopsis via repression of FT expression.

BACKGROUND: The 29-member Arabidopsis AHL gene family is classified into three main classes based on nucleotide and protein sequence evolutionary differences. These differences include the presence or absence of introns, type and/or number of conserved AT-hook and PPC domains. AHL gene family members are divided into two phylogenetic clades, Clade-A and Clade-B. A majority of the 29 members remain functionally uncharacterized. Furthermore, the biological significance of the DNA and peptide sequence diversity, observed in the conserved motifs and domains found in the different AHL types, is a subject area that remains largely unexplored. RESULTS: Transgenic plants overexpressing AtAHL20 flowered later than the wild type under both short and long days. Transcript accumulation analyses showed that 35S:AtAHL20 plants contained reduced FT, TSF, AGL8 and SPL3 mRNA levels. Similarly, overexpression of AtAHL20's orthologue in Camelina sativa, Arabidopsis' closely related Brassicaceae family member species, conferred a late-flowering phenotype via suppression of CsFT expression. However, overexpression of an aberrant AtAHL20 gene harboring a missense mutation in the AT-hook domain's highly conserved R-G-R core motif abolished the late-flowering phenotype. Data from targeted yeast-two-hybrid assays showed that AtAHL20 interacted with itself and several other Clade-A Type-I AHLs which have been previously implicated in flowering-time regulation: AtAHL19, AtAHL22 and AtAHL29. CONCLUSION: We showed via gain-of-function analysis that AtAHL20 is a negative regulator of FT expression, as well as other downstream flowering time regulating genes. A similar outcome in Camelina sativa transgenic plants overexpressing CsAHL20 suggest that this is a conserved function. Our results demonstrate that AtAHL20 acts as a photoperiod-independent negative regulator of transition to flowering.

Improving seed size, seed weight and seedling emergence in Camelina sativa by overexpressing the Atsob3-6 gene variant.

Seedling stand establishment is a critical factor affecting crop yield in low-precipitation agricultural regions. This is especially true for small seeded crops, such as Camelina (Camelina sativa) and canola (Brassica napus), that need to be planted shallow. Deeper planting would be desirable so that seeds can access soil moisture and bigger seeds could improve emergence and stand establishment by providing the energy necessary for seedling elongation. AHL (AT-Hook Containing, Nuclear Localized) genes play an important role in seedling growth and development. AHL proteins contain two structural units, the DNA-binding AT-hook motif and the Plant and Prokaryote Conserved (PPC) domain, required for protein-protein interactions. Our previous studies demonstrate that AtAHL29/SOB3 (Suppressor of phytochrome B-4 #3) regulates seedling development in Arabidopsis (Arabidopsis thaliana). Activation-tagged overexpression of AtSOB3 (Atsob3-D) represses the long-hypocotyl phenotype of an Arabidopsis phytochrome B mutant. In contrast, overexpression of the Atsob3-6 variant (Atsob3-6-OX), with a non-functional AT-hook, confers a long-hypocotyl phenotype. In this study, we demonstrate the role of Atsob3-D and Atsob3-6-OX in modulating seed size and hypocotyl length in the brassicas Arabidopsis and Camelina. In Arabidopsis, Atsob3-D reduces seed weight whereas Atsob3-6-OX increases seed weight and size when compared to the wild type. Similarly, Atsob3-6-OX transgenic Camelina seedlings are taller than the wild type, and produce larger and heavier seeds. These larger Atsob3-6-OX Camelina seeds also confer better emergence in deep-soil planting when compared to the wild type. Taken together, Atsob3-6-OX increases seed size, seed weight, seedling hypocotyl length and stand establishment in the oilseed crop Camelina.