miR396-targeted AtGRF transcription factors are required for coordination of cell division and differentiation during leaf development in Arabidopsis

Abstract

In plants, cell proliferation and polarized cell differentiation along the adaxial–abaxial axis in the primordium is critical for leaf morphogenesis, while the temporal–spatial relationships between these two processes remain largely unexplored. Here, it is reported that microRNA396 (miR396)-targeted Arabidopsis growth-regulating factors (AtGRFs) are required for leaf adaxial–abaxial polarity in Arabidopsis. Reduction of the expression of AtGRF genes by transgenic miR396 overexpression in leaf polarity mutants asymmetric leaves1 (as1) and as2 resulted in plants with enhanced leaf adaxial–abaxial defects, as a consequence of reduced cell proliferation. Moreover, transgenic miR396 overexpression markedly decreased the cell division activity and the expression of cell cycle-related genes, but resulted in an increased percentage of leaf cells with a higher ploidy level, indicating that miR396 negatively regulates cell proliferation by controlling entry into the mitotic cell cycle. miR396 is mainly expressed in the leaf cells arrested for cell division, coinciding with its roles in cell cycle regulation. These results together suggest that cell division activity mediated by miR396-targeted AtGRFs is important for polarized cell differentiation along the adaxial–abaxial axis during leaf morphogenesis in Arabidopsis.

Arabidopsis GROWTH-REGULATING FACTOR7 Functions as a Transcriptional Repressor of Abscisic Acid– and Osmotic Stress–Responsive Genes, Including DREB2A

“…Data from this study and other groups are consistent in supporting that GRF7 has negative roles in osmotic stress responses but positive roles in plant growth and development (Figures 4 and 8; see Supplemental Figure 12 online) (Liu et al, 2009;Rodriguez et al, 2010;Wang et al, 2011). Under stress conditions, many stress-inducible genes are induced and function to improve stress tolerance.…”

“…Therefore, the increased expression of osmotic stress-inducible genes seems to be the factor responsible for the osmotic stress tolerance, although it is possible that regulation of morphogenesis by GRF7 affects osmotic stress tolerance through other pathways. The regulation of plant size by GRF7 could be another such pathway, since most studies of GRF family members have revealed that GRF-deficient plants are smaller than the wild type (Kim et al, 2003;Horiguchi et al, 2005;Liu et al, 2009;Rodriguez et al, 2010;Wang et al, 2011). These reports suggest that the size reduction is due to direct regulation of plant morphogenesis by GRF family proteins.…”

Construction of MicroRNA- and MicroRNA*-mediated regulatory networks in plants

“…Certain subnetworks were extracted for further functional characterization. At first glance, numerous subnetworks were highly conserved between Arabidopsis and rice, most of which have been functionally analyzed in previous studies, such as miR159/319-TCP/MYB gene interactions, [25][26][27] 33,34 (see Fig. 9 in Fig.…”

ASYMMETRIC LEAVES2 and FASCIATA2 cooperatively regulate the formation of leaf adaxial-abaxial polarity in Arabidopsis thaliana

“…ASYMMETRIC LEAVES2 (AS2) and AS1 genes of Arabidopsis thaliana function in the formation of appropriately expanded flat symmetric leaves, with generation of the three structural axes (Byrne et al 2000(Byrne et al 2001(Byrne et al , 2002Iwakawa et al 2002;Lin et al 2003;Ori et al 2000;Rédei and Hirono 1964;Semiarti et al 2001;Tsukaya and Uchimiya 1997;Xu et al 2003). To date, various modifier mutations that generate filamentous leaves surrounded by abaxialized epidermis in the as2 or as1 mutant backgrounds have been identified [for example, enhancer of asymmetric leaves2 and asymmetric leaves1-1 (eal-1) and elongator3-27 (elo3-27), and so on], and it has been reported that the development of the adaxial domain of leaves is severely defective in these double mutants (Garcia et al 2006;Horiguchi et al 2011 a, b;Huang et al 2006;Inagaki et al 2009;Ishibashi et al 2012;Kojima et al 2011;Li et al 2005;Pinon et al 2008;Szakonyi and Byrne 2011;Ueno et al 2007;Wang et al 2011;Xu et al 2012;Yang et al 2006;Yao et al 2008;Yuan et al 2010). On the base of the extreme synthetic phenotype of the double mutants, it has been proposed that AS2 (and AS1) and modifier genes are involved in adaxial development in independent and parallel fashions during the leaf formation.…”