High impact information on HOG1

• Genes introduced into higher plant genomes can become silent (gene silencing) and/or cause silencing of homologous genes at unlinked sites (homology-dependent gene silencing or HDG silencing) [1].
• Complementation of the hog1-1 point mutation with a T-DNA containing the gene coding for SAH hydrolase restored gene silencing, HDG silencing, DNA methylation, fast growth, and normal seed viability [1].
• These results indicate that Ado must be steadily removed by ADK to prevent feedback inhibition of SAH hydrolase and maintain SAM utilization and recycling [2].
• In spinach, subcellular localization positions SAHH and ADK in the cytosol with the phospho-base N-methyltransferase activities [3].
• Another Gly betaine accumulator, sugar beet (Beta vulgaris), also showed salt-responsive increases in SAHH and ADK activities and protein whereas tobacco (Nicotiana tabacum) and canola (Brassica napus), which do not accumulate Gly betaine, did not show comparable changes in these enzymes [3].

Biological context of HOG1

• Three independent mutants of HOG1 were each found to have point mutations at the 3' end of a gene coding for S-adenosyl-l-homocysteine (SAH) hydrolase, and hog1-1 plants show reduced SAH hydrolase activity [1].
• These results imply that DNA methylation is necessary for both gene silencing and HDG silencing [4].
• Genetics of homology-dependent gene silencing in Arabidopsis; a role for methylation [5].
• These results, together with detailed analyses of the progenies from the primary transformants and supertransformants, revealed that HDGS of the resident silenced locus was caused not by simple transgene duplication, but by aberrant transcripts derived from rearranged promoters present in siJKA [6].
• Despite the presence in nature of many functional gene families that contain several to many highly similar sequences, the presence of identical DNA sequence repeats is widely thought to predispose transgene inserts to homology dependent gene silencing (HDGS) [6].

Associations of HOG1 with chemical compounds

• The insertion was identified to be in the intergenic area between loci At4G13940 and At4G13930, coding for SAHH (S-Adenosyl-l-Homocysteine Hydrolase) and SHMT (Serine Hydroxy Methyl Transferase) genes, respectively [7].
• Because SAHH activity is inhibited by its products, we propose that ADK is not a stress-responsive enzyme per se, but plays a pivotal role in sustaining transmethylation reactions in general by serving as a coarse metabolic control to reduce the cellular concentration of free adenosine [3].

Other interactions of HOG1

• In an earlier study we reported HDG silencing of chalcone synthase (CHS) in Arabidopsis [4].

References