Jumonji (JMJ) family of proteins are named after the cruciform morphology (resembling cross) of normal and abnormal neural grooves on the neural plates of jmj mutant mice, which were identified by mouse gene trap method. Members of this family are recognized by presence of two conserved domains jmjN and jmjC and AT rich DNA binding domain ARID. ARID domains play a role in DNA binding, chromatin binding or regulation at transcription level (Takeuchi et al., 1995). Only the jmjC domain or both jmjC and jmjN domains are present in more than 100 proteins belonging to bacteria, fungi, animals and plants (Balciunas and Roone., 2000). JMJ was initially identified to play a role in normal cardiogenesis by acting as a transcriptional repressor of cyclin D1 in the embryonic heart (Toyoda et al., 2003). JMJ proteins containing jmjC domain belong to the JHDMs (jmjC domain containing histone demethylases) class of histone demethylases that reversibly removes methyl group from histones reaction through an oxidative reaction requiring Fe and a-ketoglutarate as cofactors. Arabidopsis consist of 21 jmjC domain containing proteins subdivide into five groups namely: JARID1/ KDM5, JHDM3/KDM4, JDHM2/KDM3, JHDM6 and group containing just jmjC domain (Shi et al., 2004). Maize consists of 19 ZmJMJs encoding genes distributed unevenly across 9 of the all 10 maize chromosomes, and divided into three subfamilies: JARID1/ KDM5, JHDM3/KDM4 and JHDM2/KDM3 based on amino acid sequence similarity. Based on quantitative real time PCR results, all 19 ZmJMJs showed differential expression  responsive to heat stress treatment or normal condition (Qian et al., 2019).

AtJMJ14 plays role in RNA silencing, EFL6 (early flowering 6) and its homolog REF6 (relative of early flowering 6) belonging to jmjN/C domain containing proteins play a role in brassinosteroid responses, whereas other members are involved in female gametophyte development and cytosine methylation and (Pagnussat et al., 2005, Saze et al., 2008, Yu et al., 2008, Searle et al., 2010, Deleris et al., 2010) . AtJMJ30 regulates the pace of the circadian clock in Arabidopsis, since based on ChIP assay and confirmed by JMJ30 loss and gain of function mutant, morning phased clock component transcription factors CCA1 and LHY directly regulates AtJMJ30 expression repressing its activity (Lu et al., 2011). In response to heat, AtJMJ30 histone demethylase is recruited to HSP21 (Heat Shock protein 21) locus and mediates the balance between H3K27me3 and H3K4me3 by increasing levels of H3Kme3 and by removal of H3K27me3  (Yamaguchi et al., 2021).AtJMJ24 possessing ubiquitin E3 ligase activity destabilizes heterochromatic  state of silenced region by directing CHG methylation specific DNA methyltransferase CHROMOMETHYLASE 3 (CMT3) for proteasome degradation. Thus AtJMJ24 plays a role in linking histone modification and DNA methylation (Deng et al., 2016). Based on loss of function and overexpression studies,  AtJMJ24 negatively regulates silencing of transposable element (TE) AtMu1c by binding to histone H3 in vivo without demethylase activity and AtJMJ24 activity is anti correlated with H3K9me2 levels at AtMu1c (Kabelitz et al., 2016). AtJMJ27, a JHDM2 (jmjC domain-containing histone demethylase 2) protein play role in both defense and developmental processes in Arabidopsis. It exhibits H3K9me1/2 demethylase activity and is a positive regulator of pathogenesis related gene (PR), induced in response to virulent Pseudomonas syringae and Flowering Locus (FLC) and a negative regulator of defense repressor gene WRKY25 and flowering regulator CONSTANS (CO)  (Dutta et al., 2017). Also, AtJMJ14 is a positive modulator of defense genes involved in salicylic acid and pipecolic acid pathways through pathogen induced H3K4me3 enrichment (Li et al., 2019). Arabidopsis telomeric repeat binding factors (TRBs) recruit Polycomb Repressive Complex2 (PRC2) and AtJMJ14, a histone demethylase in order to repress target gene expression by H3K27me3 enrichment and H3K4me3 removal (Wang et al., 2023). Based on jmj13 mutant studies, AtJMJ13 acts as a flowering repressor in Arabidopsis in both temperature and day light dependent manner (Zheng et al., 2019). Arabidopsis AtJMJ15 plays a role in salt stress response since loss of function mutant increased salt stress sensitivity and knockout mutant affected salt stress responsive gene expression by changing H3K4me3 levels. AtJMJ15 represses WRKY46 and WRKY70, negative regulators of abiotic stress by demethylating H3K4me3 mark in promoter and coding region (Shen et al., 2022).

 Last updated June 2023 by Ankita Abnave

References:

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