PICKLEActs throughout the Plant to Repress Expression of Embryonic Traits and May Play a Role in Gibberellin-Dependent Responses

Abstract

A seed marks the transition between two developmental states; a plant is an embryo during seed formation, whereas it is a seedling after emergence from the seed. Two factors have been identified in Arabidopsis that play a role in establishment of repression of the embryonic state: PKL (PICKLE), which codes for a putative CHD3 chromatin remodeling factor, and gibberellin (GA), a plant growth regulator. Previous observations have also suggested that PKL mediates some aspects of GA responsiveness in the adult plant. To investigate possible mechanisms by which PKL and GA might act to repress the embryonic state, we further characterized the ability of PKL and GA to repress embryonic traits and reexamined the role of PKL in mediating GA-dependent responses. We found that PKL acts throughout the seedling to repress expression of embryonic traits. Although the ability of pkl seedlings to express embryonic traits is strongly induced by inhibiting GA biosynthesis, it is only marginally responsive to abscisic acid and SPY (SPINDLY), factors that have previously been demonstrated to inhibit GA-dependent responses during germination. We also observed that pkl plants exhibit the phenotypic hallmarks of a mutation in a positive regulator of a GA response pathway including reduced GA responsiveness and increased synthesis of bioactive GAs. These observations indicate that PKL may mediate a subset of GA-dependent responses during shoot development.

A transcriptional view on somatic embryogenesis

“…The pkl mutant seedlings retain embryonic traits after germination and produce somatic embryos from a number of seedling tissues, coinciding with de‐repression of the LEC genes (Henderson et al., 2004; Ogas, Kaufmann, Henderson, & Somerville, 1999). CHD3 proteins are associated with histone deacetylases in animals (Torchy, Hamiche, & Klaholz, 2015), but loss of PKL in plants was found to affect global H3K27me3 levels, also at the LEC1 and LEC2 loci, rather than acetylation levels (Zhang et al., 2008).…”

BABY BOOM target genes provide diverse entry points into cell proliferation and cell growth pathways

“…Loss-of-function mutants of the PICKLE (PKL) CHD3 chromatin-remodeling factor convert seedling roots into embryogenic tissues (Ogas et al 1999). PKL activity is not restricted to seedlings, as pkl mutants also exhibit GA-deficient shoot phenotypes (Ogas et al 1997;Henderson et al 2004), as well as ectopic activation of primordium and meristem identity genes in the carpel (Eshed et al 1999).…”

CHD3 chromatin-remodeling factor PICKLE regulates floral transition partially via modulating LEAFY expression at the chromatin level in Arabidopsis

“…PKL was shown to regulate the transition from embryonic to vegetative development in Arabidopsis (Ogas et al, 1999). pkl mutant plants exhibit some GA-deficient phenotypes, including dark green leaves with short petioles, delayed bolting and reduced apical dominance (Henderson et al, 2004). Some of the primary roots of pkl plants fail to develop normally and show some embryonic differentiation characteristics, and also accumulate triacylglycerol with a fatty acid composition which is similar to that found in seeds (Henderson et al, 2004;Rider et al, 2004).…”

“…pkl mutant plants exhibit some GA-deficient phenotypes, including dark green leaves with short petioles, delayed bolting and reduced apical dominance (Henderson et al, 2004). Some of the primary roots of pkl plants fail to develop normally and show some embryonic differentiation characteristics, and also accumulate triacylglycerol with a fatty acid composition which is similar to that found in seeds (Henderson et al, 2004;Rider et al, 2004). LEAFY COTYLEDON genes LEC1, LEC2 and FUS3 (FUSCA3), regulators of embryogenesis, are suppressed by PKL during germination, reflected by the fact that all the three transcripts are elevated significantly in primary roots of pkl mutants (Ogas et al, 1999;Rider et al, 2003).…”

“…In Arabidopsis, PICKLE (PKL) encodes a CHD3-like ATP-dependent chromatin remodeling factor (Ogas et al, 1997(Ogas et al, , 1999Henderson et al, 2004;Ho et al, 2013). PKL was shown to regulate the transition from embryonic to vegetative development in Arabidopsis (Ogas et al, 1999).…”