miR396a-Mediated Basic Helix–Loop–Helix Transcription Factor bHLH74 Repression Acts as a Regulator for Root Growth in Arabidopsis Seedlings

Abstract

miR396 targets seven GROWTH-REGULATING FACTOR (GRF) genes and the BASIC HELIX-LOOP-HELIX (bHLH) TRANSCRIPTION FACTOR 74 gene (bHLH74) in Arabidopsis. Previous research revealed that the miR396 target module regulates cell proliferation and plays a critical role in leaf development. However, no additional biological functions of miR396 have been investigated in detail. In this study, T-DNA insertion mutants and transgenic plants with altered levels of miR396 or its target genes were used to characterize the regulatory role of miR396 in root development. We found that AtMIR396a was the predominant source for miR396 accumulation in the roots of seedlings, and that the mir396a-1 mutant had longer roots than wild-type seedlings. Overexpression of AtMIR396a decreased the transcript levels of target genes such as GRF genes and bHLH74, and resulted in a shorter root phenotype. Furthermore, the bhlh74-1 mutant had shorter roots, whereas overexpression of an miR396-resistant form of bHLH74 (mbHLH74) had an enhanced root growth phenotype. Moreover, MIR396a regulated root growth by affecting the elongation zone. Taken together, these data indicate that miR396a-mediated bHLH74 repression helps regulate root growth in Arabidopsis seedlings.

MicroRNA miR396 Regulates the Switch between Stem Cells and Transit-Amplifying Cells in Arabidopsis Roots

“…However, our data show that the repression of PLT genes by the GRFs contributes to the quantitative regulation of PLT levels in the root meristem, as a reduction in the GRFs by miR396 or an increase in their levels by the use of rGRF transgenes or miR396 target mimics results in opposite changes of PLT expression levels. It is interesting that, in the most extreme cases, miR396 overexpression produces defects in cell elongation, which were also observed previously (Bao et al, 2014). Cell elongation is also inhibited by high local levels of PLT (Mähönen et al, 2014).…”

“…The miR396-GRF interaction is conserved among angiosperms and gymnosperms (Jones-Rhoades and Bartel, 2004;Debernardi et al, 2012). It has been shown that overexpression of miR396 represses organ growth in Arabidopsis (Liu et al, 2009;Rodriguez et al, 2010;Bao et al, 2014;Liang et al, 2014b), whereas increased levels of the GRFs promote growth, especially in leaves (Kim et al, 2003;Horiguchi et al, 2005;Rodriguez et al, 2010), yet the mechanisms underlying the functions of the GRFs are largely unknown.…”

The Arabidopsis miR396 mediates pathogen-associated molecular pattern-triggered immune responses against fungal pathogens

“…Although initial reports identified GRFs as transcription factors with a function in leaf and stem development, recent studies have uncovered functions of GRFs in other developmental processes such as flowering, seed and root development and regulation of plant longevity26274753545556. Also, different stresses lead to changes in miR396 accumulation, including interactions with nematodes, bacteria, oomycetes and abiotic stress, among others2844575859.…”

Transcriptome Profiling of Taproot Reveals Complex Regulatory Networks during Taproot Thickening in Radish (Raphanus sativus L.)

“…In this study, some miRNA-mRNA pair interactions were observed in radish taproot thickening process. In detail, the ARFs (targeted by miR160 and miR167), IAA11 (targeted by miR5021) and bHLH74 (targeted by miR396) were found to be involved in root growth and regulated vascular cell differentiation (Bustos Sanmamed et al, 2013; Bao et al, 2014; Zhang et al, 2014b). The LRR protein kinase-like protein gene ( LRR , targeted by miR1510 and miR6474), LACs (targeted by miR397) and EXPA9 (targeted by miR8005 and miR3447) were involved in cell wall formation and loosening (Dolan and Davies, 2004; Cai et al, 2006), while the CESA6 (targeted by miR5021) and BAM4 (targeted by miR5293) genes were involved in cell wall synthesis and degradation (Cosgrove, 2005; Van Sandt et al, 2007).…”