GROWTH-REGULATING FACTOR4 ofArabidopsis thaliana is required for development of leaves, cotyledons, and shoot apical meristem

Abstract

Previously, we identified a GROWTH-REGULATING FACTOR gone family, comprising nine members, which encodes putative transcription factors in Arabidopsis thaliana. The grfl grf2 grf3 triple mutants produced partially fused cotyaedons and developed small leaves due to a reduction in cell numbers. To understand the functional role of another member of this gone family, GRF4, we have new identified a grf4 null mutant and constructed a quadruple mutant by crossing it to the grf triple mutant. The quadruple mutant has much smaller leaves than its parental ~utants, with this reduced size again due to fewer cells. Interestinglyp the quadruple mutant displays not enny a much stronger fusion of cotyledons but also the phenotype of the shoot meristemless mutant. The aberrant cotyledons of the quadruple mutants result from a fusion of cotyledon primordia during embryogenesis. These results suggest that GRF4 is required for both Meal ce|[ proliferation and the embryonic development of cotyledons and the shoot apical meristem.

Overexpression of Brassica rapa GROWTH-REGULATING FACTOR genes in Arabidopsis thaliana increases organ growth by enhancing cell proliferation

“…These results indicate therefore that the large size of BrGRF-OX organs is due to increases in cell numbers, but not due to increases in cell size. Our data are well in agreement with previous studies in which overexpression of AtGRFs, BnGRF2, and BrGRF8 promoted cell proliferation activities and thus increased organ size (Kim and Lee 2006;Liu et al 2012;Wang et al 2014). In conclusion, the seven BrGRFs examined in this study seem to act as positive regulators of the cell proliferation process, consequently determining the final size of organs.…”

Control of cell proliferation in Arabidopsis thaliana by microRNA miR396

“…Previous studies have shown that some of the progeny of grf multiple mutants have cotyledon fusions Kim and Lee, 2006), which often appear to be related to defects in SAM function. Taken together, these data implicate the network formed by miR396, the GRFs and their interacting factors as a relevant regulator of meristem function, at least partially through the control of cell proliferation.…”

“…The function of the GRFs as regulators of cell number in leaves is well established based on the phenotypes of grf (Horiguchi et al, 2005;Kim et al, 2003;Kim and Lee, 2006) and gif (Horiguchi et al, 2005;Kim and Kende, 2004) mutants, and plants with high miR396 levels (Liu et al, 2009). Here, we have extended these observations and found that the GRFs regulate cell proliferation in the SAM, which at least partially explains the lack of a functional meristem in an3-1 mutants overexpressing miR396 (this study) and in grf multiple knock-outs Kim and Lee, 2006). Analysis of the transcriptome of moderate miR396 overexpressers has shown that the downregulation of mitosis-specific genes is one of the main molecular effects of high miR396 levels.…”

The Arabidopsis MicroRNA396-GRF1/GRF3 Regulatory Module Acts as a Developmental Regulator in the Reprogramming of Root Cells during Cyst Nematode Infection

“…The miR396 family, miR396a and miR396b, governs the expression of seven GrowthRegulating Factor (GRF) genes (Jones- Rhoades and Bartel, 2004). The GRF gene family in Arabidopsis is known to act in a functionally redundant fashion to positively control cell proliferation and size in leaves Kim and Kende, 2004;Horiguchi et al, 2005;Kim and Lee, 2006). Consistent with the fact that miR396 acts as a negative regulator of GRF gene expression, overexpression of miR396 negatively impacted cell proliferation in leaves and meristem size (Liu et al, 2009;Rodriguez et al, 2010).…”