The LONELY GUY gene family: from mosses to wheat, the key to the formation of active cytokinins in plants

Abstract

LONELY GUY (LOG) was first identified in a screen of rice mutants with defects in meristem maintenance. In plants, LOG codes for cytokinin riboside 5 0 -monophosphate phosphoribohydrolase, which converts inactive cytokinin nucleotides directly to the active free bases. Many enzymes with the PGGxGTxxE motif have been misannotated as lysine decarboxylases; conversely not all enzymes containing this motif are cytokinin-specific LOGs. As LOG mutants clearly impact yield in rice, we investigated the LOG gene family in bread wheat. By interrogating the wheat (Triticum aestivum) genome database, we show that wheat has multiple LOGs. The close alignment of TaLOG1, TaLOG2 and TaLOG6 with the X-ray structures of two functional Arabidopsis thaliana LOGs allows us to infer that the wheat LOGs 1-11 are functional LOGs. Using RNA-seq data sets, we assessed TaLOG expression across 70 tissue types, their responses to various stressors, the pattern of cis-regulatory elements (CREs) and intron/exon patterns. TaLOG gene family members are expressed variously across tissue types. When the TaLOG CREs are compared with those of the cytokinin dehydrogenases (CKX) and glucosyltransferases (CGT), there is close alignment of CREs between TaLOGs and TaCKXs reflecting the key role of CKX in maintaining cytokinin homeostasis. However, we suggest that the main homeostatic mechanism controlling cytokinin levels in response to biotic and abiotic challenge resides in the CGTs, rather than LOG or CKX. However, LOG transgenics and identified mutants in rice variously impact yield, providing interesting avenues for investigation in wheat.

Genetic analysis of morphological traits in spring wheat from the Northeast of China by a genome-wide association study

“…Of these, a cytokinin riboside 5′-monophosphate phosphoribohydrolase ( TraesCS1A01G362500 ) was identified in the LD decay of the loci on chromosome 1A (556.0–587.4 Mb). The cytokinin is a positive regulator of shoot growth ( Chen et al, 2021 ) and response to biotic and abiotic stressors ( Ellis et al, 2005 ; Chen et al, 2022 ). Besides, the gene TraesCS2B01G123800 was identified as the candidate gene for the loci 2B (91.0–92.6 Mb) and encodes the C2H2 zinc finger, which is important for determining the prostrate/erect plant morphology ( Li et al, 2021 ).…”

Zeatin: The 60th anniversary of its identification

“…Moreover, it is now recognized that the formation of the cytokinin nucleotides is the first committed step in the biosynthetic pathway catalyzed by IPT ( Kakimoto 2001 ; Takei et al 2001 ). As the cytokinin nucleotides are converted directly by LONELY GUY (LOG) to the active cytokinin-free bases ( Kurakawa et al 2007 ; Kuroha et al 2009 ; Chen et al 2022 ), their retention intact should be informative. If the nucleotides are degraded during extraction to release cytokinin ribosides, the nucleotides will be under-estimated and the ribosides over-estimated in samples.…”

“…Relevant here is the recent challenge to ZR as merely a transport form and the suggestion by Nguyen et al (2021) that ZR is an active form. Both Romanov and Schmülling (2021) and Chen et al (2022) challenged this proposal stating it is unlikely that ZR is an active form per se, as it is unlikely to bind with sufficient efficacy to cytokinin receptors.…”

Cytokinins: Wide-Spread Signaling Hormones from Plants to Humans with High Medical Potential

“…Isoprenoid cytokinins are present in all plants, whereas aromatic CKs with N6-benzyl substituents have only been found in certain taxa [ 31 , 32 ], there are two types of CKs: adenine-type CKs represented by kinetin, zeatin, and 6-benzylaminopurine, and phenylurea-type CKs such as diphenylurea and thidiazuron (TDZ) [ 33 ]. For the activation of CKs, cytokinin riboside 5′-monophosphate phosphoribohydrolases are required, in which this enzyme converts inactive cytokinin nucleotides directly into the active free bases and regulating the actions, biosynthesis, and activity of CKs [ 34 , 35 , 36 , 37 , 38 ].…”