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

Abstract

The establishment of adaxial-abaxial polarity in the early stage of leaf development is important for the expansion of lamina. In Arabidopsis thaliana, asymmetric leaves2 (as2) and as1 mutations cause defects in the leaf adaxialabaxial polarity, which are exhibited as abaxialized filamentous leaves in the various modifier mutant backgrounds. Several modifier single mutants generate pointed leaves in common. Mutations in FASCIATA2 (FAS2) also cause pointed leaves. The FAS2 gene encodes a component of Chromatin Assembly Factor-1 (CAF-1), a histone chaperone, which affects mRNA levels of various genes through the regulation of chromatin states. In the present study, we demonstrate that as2 fas2 double mutants frequently generate abaxialized filamentous leaves and show increased mRNA levels of genes for leaf abaxialization, KANADI1 (KAN1), KAN2, YABBY5 (YAB5), ETTIN/AUXIN RESPONSE FACTOR3 (ETT/ARF3) and ARF4. In addition, the transcript levels of all four class 1 KNOTTED1-like homeobox genes that are involved in the maintenance of shoot apical meristem and the Kip-related Protein2 (KRP2) and KRP5 genes that are involved in the cell cycle progression are elevated in the as2 fas2. The mRNA levels of all genes other than YAB5, whose transcript levels rise in as2 fas2, were increased in the fas2 single mutants. Our data suggest that FAS2 participates in the establishment of leaf adaxial-abaxial polarity through the repression of the transcript levels of these genes on the as2 background.

A genetic link between epigenetic repressor AS1–AS2 and DNA replication factors in establishment of adaxial–abaxial leaf polarity of <i>Arabidopsis</i>

“…We quantified transcripts of PHABULOSA (PHB), one of the genes in the HD-ZIP III family that specify the adaxial cell fate; ETT/ARF3, ARF4, KANADI2 (KAN2), FIL, YABBY5 (YAB5) genes that specify the abaxial cell fate; and the BP, KNAT2, SHOOT MERISTEMLESS (STM) genes, which are members of the class 1 KNOX gene family and are expressed in the SAM and its periphery in wild-type plants. As shown in Figure 3, the transcript levels of BP, KAN2, FIL and YAB5 genes were significantly increased in the as2-1 mutant compared with those in Col-0 (wild-type) plant, consistent with our previous report (Kojima et al 2011;Ishibashi et al 2013). The transcript levels of KNAT2, STM, ETT/ARF3, ARF4, KAN2 genes were increased in the icu2-1 mutant compared with those in Col-0 (wildtype) plant.…”

The complex of ASYMMETRIC LEAVES (AS) proteins plays a central role in antagonistic interactions of genes for leaf polarity specification in Arabidopsis

“…Many mutations that enhance leaf polarity defects of as1 and as2 have been isolated and characterized, which is reminiscent of the presence of the cold‐sensitive pathway in the original phan mutant of Antirrhinum and handlebars as the enhancer mutation of phan . The causative genes are designated as modifiers of AS1 and AS2 and, as listed in Table they include those for biogenesis of tasiR‐ARF, biogenesis of ribosomes, chromatin modification and nucleosome assembly proteasome‐mediated protein degradation, genomic stability, and cell proliferation. Prominent phenotypes in almost all double mutants with as2 and a modifier mutation involve the generation of filamentous leaf‐like organs (Figure (b)), which are surrounded by an abaxialized epidermis and possess no or markedly premature vascular tissues.…”

“…Therefore, the synergistic repression of these ARFs is achieved by the two independent pathways, AS1–AS2 and factors involved in small RNA biogenesis such as RDR6 , AGO7 , and DCL4 , as illustrated in Figure . Molecular mechanisms for the prominent repression by other modifiers and AS1–AS2 have yet to be elucidated, but they might be involved in such repression through independent pathways (Figure ). It might be worthwhile, however, to stress that modifier mutations so far identified are weak alleles of genes that are essential for cell viability or, conversely, strong alleles of one of the functionally redundant members of such essential gene families.…”

SIMON: Simple methods for analyzing DNA methylation by targeted bisulfite next-generation sequencing

“…We outcrossed as2-1 with Col-0 three times and used the progeny for our experiments (Kojima et al 2011). Details of top1α-1, fas2-2, rh10-1, as2-1 rh10-1 were described previously (Ishibashi et al 2013;Matsumura et al 2016;Takahashi et al 2002). The top1α-1 as2-1 and top1α-1 as1-1 double mutants were generated by crossing each single mutant.…”