Abstract
Plant height is an important agronomic and horticultural trait that impacts plant productivity, durability and esthetic appeal. A number of the plant hormones such as gibberellic acid (GA), auxin and ethylene have been linked to control of plant architecture and size. Reduction in GA synthesis and auxin transport result in dwarfism while ethylene may have a permissive or repressive effect on tissue growth depending upon the age of plant tissues or the environmental conditions considered. We describe here an activation-tagged mutant of Populus tremula x P. alba clone 717-1B4 identified from 2000 independent transgenic lines due to its significantly reduced growth rate and smaller leaf size. Named dwarfy, the phenotype is due to increased expression of PtaACC SYNTHASE8, which codes for an enzyme in the first committed step in the biosynthesis of ethylene. Stems of dwarfy contain fiber and vessel elements that are reduced in length while leaves contain fewer cells. These morphological differences are linked to PtaACS8 inducing different transcriptomic programs in the stem and leaf, with genes related to auxin diffusion and sensing being repressed in the stem and genes related to cell division found to be repressed in the leaves. Altogether, our study gives mechanistic insight into the genetics underpinning ethylene-induced dwarfism in a perennial model organism.
Highlights
Reduced plant height, or dwarfism, is an important agronomic trait linked to higher yields (Huang et al, 1996; Yang and Hwa, 2008), easier harvesting (Adkins et al, 2010) and reduced nutrient demand on soils (Sieling and Kage, 2008)
Within a window of ±20 Kb around the T-DNA, 3 genes annotated in Phytozome (Figure 1C) were found as follows: a gene of unknown function (Potri.002G11400; +14.4 Kb up-stream), PtaACC SYNTHASE8 (PtaACS8; Potri.002G113900; 13.1 Kb down-stream) and PtaEARLY-RESPONSE TO DEHYDRATION 4 (ERD4; Potri.002G113800; 16.9 Kb down-stream)
We characterize a mutant line of P. tremula x P. alba clone 717-1B4 that exhibits higher transcript accumulation of PtaACS8 and that produces a significantly higher level of ethylene in all aerial tissues as compared to wild-type trees
Summary
Dwarfism, is an important agronomic trait linked to higher yields (Huang et al, 1996; Yang and Hwa, 2008), easier harvesting (Adkins et al, 2010) and reduced nutrient demand on soils (Sieling and Kage, 2008). Is linked to productivity, predation (Faeth, 1991) and the water status of the plant (Scoffoni et al, 2011) While both height and leaf size are complex traits, they appear to be genetically regulated by a similar panel of plant hormones (Valdovinos et al, 1967; Ephritikhine et al, 1999; Qi et al, 2011; Luo et al, 2013) and cytochrome P450s (Zhang et al, 2014), as well as abiotic factors such as temperature (Yang et al, 2014) and photoperiod (Li et al, 2014). Reductions in organ size are a result of two different physiological phenomena: smaller cells and impeded cellular division (Beemster et al, 2003) These two factors may work independently or synergistically to affect plant stature and organ size (Beemster et al, 2005; Skirycz et al, 2010). Altered expression of genes such as ARABIDOPSIS VACUOLAR H+-PYROPHOSPHATASE1 (AVP1; Li et al, 2005), CYTOKININ RESISTANT1 (CNR1; Guo et al, 2010), and ISOPENTENYL TRANSFERASE3 (IPT3; Nobusawa et al, 2013) impact tissue size due to a difference in the total number of cells produced, while EXPANSIN10 (EXP10; Cho and Cosgrove, 2000), ARGOS-LIKE (Hu et al, 2006), and RETINOBLASTOMA-RELATED PROTEIN1 (RBR1; Sabelli et al, 2013) change the final size of plant tissues as a function of altered cell expansion
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