Arabidopsis poly(A) polymerase PAPS1 limits founder‐cell recruitment to organ primordia and suppresses the salicylic acid‐independent immune response downstream of EDS1/PAD4

Abstract

SUMMARYPolyadenylation of pre-mRNAs by poly(A) polymerase (PAPS) is a critical process in eukaryotic gene expression. As found in vertebrates, plant genomes encode several isoforms of canonical nuclear PAPS enzymes. In Arabidopsis thaliana these isoforms are functionally specialized, with PAPS1 affecting both organ growth and immune response, at least in part by the preferential polyadenylation of subsets of pre-mRNAs. Here, we demonstrate that the opposite effects of PAPS1 on leaf and flower growth reflect the different identities of these organs, and identify a role for PAPS1 in the elusive connection between organ identity and growth patterns. The overgrowth of paps1 mutant petals is due to increased recruitment of founder cells into early organ primordia, and suggests that PAPS1 activity plays unique roles in influencing organ growth. By contrast, the leaf phenotype of paps1 mutants is dominated by a constitutive immune response that leads to increased resistance to the biotrophic oomycete Hyaloperonospora arabidopsidis and reflects activation of the salicylic acid-independent signalling pathway downstream of ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1)/PHYTOALEXIN DEFICIENT4 (PAD4). These findings provide an insight into the developmental and physiological basis of the functional specialization amongst plant PAPS isoforms.

Novel allelic variants in ACD6 cause hybrid necrosis in local collection of Arabidopsis thaliana

“…Whole rosettes of three biological replicates of 3-wk-old F 1 hybrids (Alt-1 9 Rue3.1-26) and their parental lines grown at 21°C : 17°C (day : night) at LD conditions were harvested. Phytohormone extraction was performed according to Trost et al (2014) with the following modifications. Instead of 250 mg, 50-100 mg of deep-frozen powdered material was used.…”

The poly(A) polymerase PAPS1 interacts with the RNA‐directed DNA‐methylation pathway in sporophyte and pollen development

“…Evidence for such functional specialization amongst the canonical nuclear PAPS isoforms has emerged in A. thaliana (Vi et al ., ; Kappel et al ., ; Czesnick and Lenhard, ). Mutations in PAPS1 result in opposite effects on leaf and flower growth, with moderately reduced PAPS1 function leading to smaller leaves, yet larger flowers; the smaller leaves result from both a reduced SMALL AUXIN UP RNA ( SAUR ) activity and a constitutive immune response dependent on signalling by the two lipase‐like proteins ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) and PHYTOALEXIN DEFICIENT4 (PAD4) (Trost et al ., ; Vi et al ., ). A further reduction in PAPS1 function causes more severe growth inhibition in seedlings, and a complete loss of PAPS1 function results in a fully penetrant male gametophytic defect (Vi et al ., ).…”

Size Control in Plants—Lessons from Leaves and Flowers

“…Thus, TMK defects cause a reduced leaf size while the flower size is unimpaired. Opposite organ-size defects have been shown in the poly(A) polymerase mutant paps1, which produces small leaves attributable to a cell-size defect and larger petals attributable to an increased number of cells, resulting at least partly from an increase in the number of founder cells in the petal anlage (Vi et al 2013;Trost et al 2014). At the molecular level, PAPS1 has been suggested to polyadenylate specific subsets of pre-mRNAs that vary between the different organs.…”

“…Assuming a limited number of cell cycles, final organ size could also be influenced by the initial number of cells recruited from the SAM to the emerging primordium. The primary size of the founder cell cluster varies between plant species (Dolan and Poethig 1998), and for one petalsize and two leaf-size mutants of Arabidopsis, an altered primordium size could be shown to correlate with changes in final organ size (Autran et al 2002;Eloy et al 2012;Trost et al 2014). A third model assumes that the duration of the cell proliferation period is fixed, allowing cells to proliferate only for a limited amount of time.…”