Knockdown of a JmjC domain-containing gene JMJ524 confers altered gibberellin responses by transcriptional regulation of GRAS protein lacking the DELLA domain genes in tomato.

Jinhua Li,Zhibiao Ye,Long Cui,Junhong Zhang,Bo Ouyang,Zhidan Luo,Chuying Yu,Hua Wu

doi:10.1093/jxb/eru493

Jinhua Li, Zhibiao Ye + Show 6 more

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https://doi.org/10.1093/jxb/eru493

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Plants integrate responses to independent hormonal and environmental signals to survive adversity. In particular, the phytohormone gibberellin (GA) regulates a variety of developmental processes and stress responses. In this study, the Jumonji-C (JmjC) domain-containing gene JMJ524 was characterized in tomato. JMJ524 responded to circadian rhythms and was upregulated by GA treatment. Knockdown of JMJ524 by RNAi caused a GA-insensitive dwarf phenotype with shrunken leaves and shortened internodes. However, in these transgenic plants, higher levels of endogenous GAs were detected. A genome-wide gene expression analysis by RNA-seq indicated that the expression levels of two DELLA-like genes, SlGLD1 ('GRAS protein Lacking the DELLA domain') and SlGLD2, were increased in JMJ524-RNAi transgenic plants. Nevertheless, only the overexpression of SlGLD1 in tomato resulted in a GA-insensitive dwarf phenotype, suggesting that SlGLD1 acts as a repressor of GA signalling. This study proposes that JMJ524 is required for stem elongation by altering GA responses, at least partially by regulating SlGLD1.

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Phytohormone gibberellins (GAs) are fundamentally involved in various aspects of plant growth and development, including internode elongation (Hedden and Kamiya, 1997; Xiao et al, 2006)
The phylogenetic tree constructed based on the amino acid sequences of JMJ524 and JmjC proteins from other representative organisms (Arabidopsis thaliana, human, and rice) showed that JMJ524 was significantly correlated with its counterpart Arabidopsis AtJMJ30 protein, whereas it was most distant from human HsKDM6A protein (Fig. 1B)
Similar to other JmjC domain-containing proteins, JMJ524 is highly conserved in different species (Fig. 1A), and a phylogenetic tree revealed that JMJ524 was closely related to JMJ30 and JMJD5 from Arabidopsis and human, respectively (Fig. 1B)

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Phytohormone gibberellins (GAs) are fundamentally involved in various aspects of plant growth and development, including internode elongation (Hedden and Kamiya, 1997; Xiao et al, 2006). The bioactive isoforms of GA include GA1, GA3, GA4, and GA7, in which GA12 and GA53 are the main precursors converted to various GA intermediates (e.g. GA9 and GA20) and bioactive GAs (e.g. GA1 and GA4) by GA 20-oxidases (GA20ox) and GA 3-oxidases (GA3ox), respectively. 2-oxidase (GA2ox) plays a major role in converting active GAs (GA1 and GA4) and their precursors (GA9 and GA20) to inactive forms (Sun, 2011; Raddatz et al, 2013). Bioactive GAs can trigger a plant GA response in which DELLA proteins play a major role. With bioactive GAs, the GA receptor GID1 can bind GA in the nucleus and/or cytoplasm (Sun, 2010). If the binding occurs in the cytoplasm, the GID1-GA complex induces traffic to the nucleus, binding the nuclearlocalized DELLA proteins. Once the DELLA protein binds to the GID1-GA complex, ubiquitin E3 ligase complex SCF recognizes and ubiquitinates the former, which is

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