Abstract
Plant somatic cells can be reprogrammed into totipotent embryonic cells that are able to form differentiated embryos in a process called somatic embryogenesis (SE), by hormone treatment or through overexpression of certain transcription factor genes, such as BABY BOOM (BBM). Here we show that overexpression of the AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED 15 (AHL15) gene induces formation of somatic embryos on Arabidopsis thaliana seedlings in the absence of hormone treatment. During zygotic embryogenesis, AHL15 expression starts early in embryo development, and AH15 and other AHL genes are required for proper embryo patterning and development beyond the globular stage. Moreover, AHL15 and several of its homologs are upregulated and required for SE induction upon hormone treatment, and they are required for efficient BBM-induced SE as downstream targets of BBM. A significant number of plants derived from AHL15 overexpression-induced somatic embryos are polyploid. Polyploidisation occurs by endomitosis specifically during the initiation of SE, and is caused by strong heterochromatin decondensation induced by AHL15 overexpression.
Highlights
Plant somatic cells can be reprogrammed into totipotent embryonic cells that are able to form differentiated embryos in a process called somatic embryogenesis (SE), by hormone treatment or through overexpression of certain transcription factor genes, such as BABY BOOM (BBM)
AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED 15 (AHL15) was originally identified in a yeast one-hybrid screen, and functional analysis revealed that overexpression of the gene in Arabidopsis thaliana (Arabidopsis) under control of the 35S promoter (p35S:AHL15) results in induction of SE on germinating seedlings[26]
The majority of the immature zygotic embryos (IZEs) produced non-embryogenic calli that were not observed in the other genotypes (Fig. 3e). These results indicate that AHL15 and several homologs are required for 2,4-D-induced somatic embryo formation starting from IZEs
Summary
Plant somatic cells can be reprogrammed into totipotent embryonic cells that are able to form differentiated embryos in a process called somatic embryogenesis (SE), by hormone treatment or through overexpression of certain transcription factor genes, such as BABY BOOM (BBM). We show that overexpression of the AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED 15 (AHL15) gene induces formation of somatic embryos on Arabidopsis thaliana seedlings in the absence of hormone treatment. During the past two decades, several genes have been identified that can induce SE on cultured immature zygotic embryos or seedlings when overexpressed in the model plant Arabidopsis thaliana[6,10] Several of these genes, including BABY BOOM (BBM) and LEAFY COTYLEDON 1 (LEC1) and LEC2, have been recognized as key regulators of SE11–14. We show that overexpression of Arabidopsis AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED 15 (AHL15) can induce somatic embryos (SEs) on germinating seedlings in the absence of plant growth regulators. Our data show that AHL15 has a role in chromatin opening, and that its overexpression induces SE coinciding with endomitosis and polyploidy
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