Lichen Wang, Nian Liu, Tianyi Wang, Jianying Li, Tianwang Wen, Xiyan Yang*, Keith Lindsey, Xianlong Zhang.2017.Journal of Experimental Botany
Abstract
MicroRNAs (miRNAs) modulate many biological processes through
inactivation of specific mRNA targets such as those encoding transcription
factors (TFs). A delicate spatial/temporal balance between specific miRNA and
target is central to achieving the appropriate biological outcomes. Somatic
embryogenesis (SE) in cotton (Gossypiumhirsutum), which goes through initial
cellular dedifferentiation, callus proliferation and somatic embryo
development, is of great importance for both fundamental research and for
biotechnological applications. In this study, we characterize the function of
the GhmiR157a/GhSPL10 miRNA-TF module during SE in cotton. We show that
overexpression of GhSPL10, a target of GhmiR157a, increases free auxin and
ethylene content and expression of associated signalling pathways, the
activation of the flavonoid biosynthesis pathway, and promotes initial cellular
dedifferentiation and callus proliferation. Inhibition of expression of the
flavonoid synthesis gene F3H in GhSPL10 overexpression line (35S:rSPL10-7)
blocked callus initiation, while exogenous application of several types of
flavonols promoted callus proliferation, associated with cell cycle related
gene expression. Inhibition of ethylene synthesis by AVG treatment in
35S:rSPL10-7 line severely inhibited callus initiation, while activation of
ethylene signaling through ACC treatment, EIN2 overexpression, or inhibition of
the ethylene negative regulator CTR1 by RNAi all promoted flavonoid-related
gene expression and flavonol accumulation. These results show that an
upregulation of ethylene signaling and the activation of flavonoid biosynthesis
in GhSPL10 overexpression lines were associated with initial cellular
dedifferentiation and callus proliferation. Our results demonstrate the
importance of a GhmiR157a/GhSPL10 gene module in regulating SE via hormonal and
flavonoid pathways.