The early inflorescence of Arabidopsis thaliana demonstrates positional effects in floral organ growth and meristem patterning

Abstract

Key messageLinear modelling approaches detected significant gradients in organ growth and patterning across early flowers of the Arabidopsis inflorescence and uncovered evidence of new roles for gibberellin in floral development.AbstractMost flowering plants, including the genetic model Arabidopsis thaliana, produce multiple flowers in sequence from a reproductive shoot apex to form a flower spike (inflorescence). The development of individual flowers on an Arabidopsis inflorescence has typically been considered as highly stereotypical and uniform, but this assumption is contradicted by the existence of mutants with phenotypes visible in early flowers only. This phenomenon is demonstrated by mutants partially impaired in the biosynthesis of the phytohormone gibberellin (GA), in which floral organ growth is retarded in the first flowers to be produced but has recovered spontaneously by the 10th flower. We presently lack systematic data from multiple flowers across the Arabidopsis inflorescence to explain such changes. Using mutants of the GA 20-OXIDASE (GA20ox) GA biosynthesis gene family to manipulate endogenous GA levels, we investigated the dynamics of changing floral organ growth across the early Arabidopsis inflorescence (flowers 1–10). Modelling of floral organ lengths identified a significant, GA-independent gradient of increasing stamen length relative to the pistil in the wild-type inflorescence that was separable from other, GA-dependent effects. It was also found that the first flowers exhibited unstable organ patterning in contrast to later flowers and that this instability was prolonged by exogenous GA treatment. These findings indicate that the development of individual flowers is influenced by hitherto unknown factors acting across the inflorescence and also suggest novel functions for GA in floral patterning.Electronic supplementary materialThe online version of this article (10.1007/s00497-017-0320-3) contains supplementary material, which is available to authorized users.

An ABA-GA bistable switch can account for natural variation in the variability of Arabidopsis seed germination time

“…Previously it was shown that, in some Arabidopsis accessions, seeds matured on primary 24 inflorescences had different germination behaviours to those that developed on branches (Boyd et 25 al., 2007). It was also reported recently that some mutants defective in GA biosynthesis show graded 26 developmental differences along the inflorescence (Plackett et al, 2018). Here we show that 27 variability in germination time exists even for seeds from the same silique of Arabidopsis, suggesting 28 that it is not generated by developmental gradients in the plant.…”

The makings of a gradient: spatiotemporal distribution of gibberellins in plant development

“…The need for gibberellins to be depleted from specific cells can be demonstrated by examining the phenotypes of wild-type Arabidopsis plants treated with exogenous gibberellins (e.g. [ 52 ]), gibberellin catabolism mutants [ 14 , 16 ], and higher-order mutants lacking all five DELLAs [ 53 • ]. Surprisingly for a growth regulatory hormone, each of these interventions results in broadly normal plant growth and development, perhaps indicating that gibberellin responses in Arabidopsis might be largely saturated under optimal growth conditions.…”

“…Surprisingly for a growth regulatory hormone, each of these interventions results in broadly normal plant growth and development, perhaps indicating that gibberellin responses in Arabidopsis might be largely saturated under optimal growth conditions. Nevertheless, ectopically increased gibberellins and loss of DELLAs consistently leads to altered organ size and fertility defects that are presumably a consequence of disruptions in normal spatiotemporal patterning of gibberellins [ 14 , 16 , 52 , 53 • ]. In the future, it will be fascinating to resolve how patterns of gibberellin biosynthetic, catabolic, and transport activities contribute to spatiotemporal distributions of gibberellins.…”

A phylogenetically conserved APETALA2/ETHYLENE RESPONSE FACTOR, ERF12, regulates Arabidopsis floral development

“…The timing of stamen founder cell specification is unknown; auxin response maxima have been spatially associated with early developmental time points, but the founder-cell marker DRNL is expressed prior to DR5 and non-robust positional information might result from the imprecise resolution of initially diffuse expression domains of positional regulators. Floral organ number and increased organ fusion and homeosis in wild-type Arabidopsis are enhanced by GA treatment (Plackett et al 2018) and the most common homeotic conversions are petalloid stamens . Variable organ numbers in first-formed wild type flowers probably represents variable molecular stochasticity in expression levels or boundaries of homeotic or other regulatory genes (Kitazawa and Fujimoto 2014), especially considering the close proximity of petal and lateral stamen founder cell populations .…”