Transcriptional, Posttranscriptional, and Posttranslational Regulation of SHOOT MERISTEMLESS Gene Expression in Arabidopsis Determines Gene Function in the Shoot Apex

Abstract

The activity of SHOOT MERISTEMLESS (STM) is required for the functioning of the shoot apical meristem (SAM). STM is expressed in the SAM but is down-regulated at the site of leaf initiation. STM is also required for the formation of compound leaves. However, how the activity of STM is regulated at the transcriptional, posttranscriptional, and posttranslational levels is poorly understood. We previously found two conserved noncoding sequences in the promoters of STM-like genes across angiosperms, the K-box and the RB-box. Here, we characterize the function of the RB-box in Arabidopsis (Arabidopsis thaliana). The RB-box, along with the K-box, regulates the expression of STM in leaf sinuses, which are areas on the leaf blade with meristematic potential. The RB-box also contributes to restrict STM expression to the SAM. We identified FAR1-RELATED SEQUENCES-RELATED FACTOR1 (FRF1) as a binding factor to the RB-box region. FRF1 is an uncharacterized member of a subfamily of four truncated proteins related to the FAR1-RELATED SEQUENCES factors. Internal deletion analysis of the STM promoter identified a region required to repress the expression of STM in hypocotyls. Expression of STM in leaf primordia under the control of the JAGGED promoter produced plants with partially undifferentiated leaves. We further found that the ELK domain has a role in the posttranslational regulation of STM by affecting the nuclear localization of STM.

Evolution, diversification, and expression of KNOX proteins in plants

“…Therefore, it is possible that the STM originated at an earlier stage in the evolution of dicotyledons, and was lost in monocotyledons. In Arabidopsis and other higher plants, the STM gene is highly expressed in SAM (Elhiti et al, 2013 ; Stammler et al, 2013 ; Aguilar-Martinez et al, 2015 ). In G. max , two STM homologs are strongly expressed in the SAM and others are not specific to SAM.…”

A high-resolution gene expression atlas links dedicated meristem genes to key architectural traits

“…4B,C). Among them are the GeBP, FARL, NAC, and Homeobox (HB) TFs, which have a demonstrated link to meristem function (Vollbrecht et al 2000;Aida and Tasaka 2006;Chevalier et al 2008;Aguilar-Martínez et al 2014). Mean expression for the remaining six families is negatively correlated with PC1, suggesting that they act as repressors of meristem identity and/or promote organogenesis.…”

FAR1-RELATED SEQUENCE (FRS) and FRS-RELATED FACTOR (FRF) Family Proteins in Arabidopsis Growth and Development

“…Recent studies have demonstrated that FHY3 and FAR1 play multiple roles in a wide range of cellular processes, including light signal transduction, photomorphogenesis ( Wang and Deng, 2002 ; Lin et al, 2007 ), circadian clock and flowering time regulation ( Li et al, 2011 ), shoot meristem and floral development ( Li et al, 2016 ), chloroplast division ( Ouyang et al, 2011 ), chlorophyll biosynthesis ( Tang et al, 2012 ), starch synthesis ( Ma et al, 2017 ), abscisic acid responses ( Tang et al, 2013 ), oxidative stress responses ( Ma et al, 2016 ), plant immunity ( Wang et al, 2016 ), and the low-phosphate response ( Liu Y. et al, 2017 ), indicating that FHY3 and FAR1 are crucial for plant growth and development ( Table 1 ). In addition, 12 FAR1-RELATED SEQUENCE (FRS) and four FRS-RELATED FACTOR (FRF) family proteins were identified in Arabidopsis thaliana ( Lin and Wang, 2004 ; Aguilar-Martinez et al, 2015 ). Besides FHY3 and FAR1, the physiological and molecular mechanisms of most FRS and FRF family proteins remain largely unknown in plants.…”