Silencing of the tobacco pollen pectin methylesterase NtPPME1 results in retarded in vivo pollen tube growth

Abstract

Sperm delivery in flowering plants requires extensive pollen tube growth through the female sporophytic tissues of the pistil. The apical cell wall emerges as a central player in the control of pollen tube growth, since it provides strength to withstand the internal turgor pressure, while imparting sufficient plasticity to allow cell wall extension through the incorporation of new membrane and wall material. Within this scenario, pectin methylesterases (PMEs; EC 3.1.1.11) emerge as crucial regulators in determining the mechanical properties of pectins, the major component of the apical pollen tube wall. We previously identified NtPPME1, a pollen specific PME from Nicotiana tabacum. Here we show that silencing of NtPPME1 results in a mild but significant decrease of in vivo pollen tube growth while the overall PME activity in pollen is not significantly affected. Although the precise mechanisms responsible for the observed phenotype are not known, it seems likely that the cell must maintain a closely regulated level of PME activity in order to maintain the equilibrium between strength and plasticity in the apical cell wall. A relatively minor disturbance of this equilibrium, as caused by NtPPME1 silencing, compromises pollen tube growth.

Overexpression of Pectin Methylesterase Inhibitors in Arabidopsis Restricts Fungal Infection by Botrytis cinerea

“…Segregation analysis of the marker gene bar for resistance to the herbicide Basta in the self-crossed T2 progeny showed either a 3:1 Mendelian segregation ratio (1-1, 2-7, 2-9, and 2-15 lines) or a 15:1 segregation ratio (1-5 and 1-43 lines). These ratios correspond to one and two independent insertions of the transgene, respectively, and suggest a normal fitness of transformed pollen grains during fertilization (Bosch and Hepler, 2006). Lines 1-1 and 1-5 and lines 2-7 and 2-9 expressed levels of AtPMEI-1 or AtPMEI-2 transcripts about 90 and 200 times higher, respectively, than wild-type plants.…”

“…Plant PMEs are involved in important physiological processes such as microsporogenesis, pollen growth, pollen separation, seed germination, root development, polarity of leaf growth, stem elongation, fruit ripening, and loss of tissue integrity (Tieman and Handa, 1994;Wen et al, 1999;Micheli et al, 2000;Pilling et al, 2000Pilling et al, , 2004Micheli, 2001;Bosch et al, 2005;Jiang et al, 2005;Bosch and Hepler, 2006;Francis et al, 2006;Tian et al, 2006). They may also have a role in resistance to fungal and bacterial pathogens (McMillan et al, 1993;Boudart et al, 1998;Wietholter et al, 2003) and are required for the systemic spread of Tobacco mosaic virus through the plant (Dorokhov et al, 1999;Chen et al, 2000;Chen and Citovsky, 2003).…”

Profiling of Translatomes of in Vivo–Grown Pollen Tubes Reveals Genes with Roles in Micropylar Guidance during Pollination in Arabidopsis

“…In tobacco, a pollen pectin methylesterase gene, PPME1, is responsible for maintenance of the equilibrium between strength and plasticity in the apical pollen tube cell wall, as antisense inhibition of Nt-PPME1 expression caused a mild but decreased in vivo pollen tube elongation (Bosch and Hepler, 2006). The germination and growth of iv2 pollen tubes, genotyped by GUS staining in the SAIL background, was normal under in vitro culture conditions ( Figure 6B).…”

Restoration of Mature Etiolated Cucumber Hypocotyl Cell Wall Susceptibility to Expansin by Pretreatment with Fungal Pectinases and EGTA in Vitro

“…Application of an exogenous PME induced thickening of the apical cell wall and inhibited pollen tube growth (Bosch et al, 2005). Silencing of the tobacco pollen PME NtPPME1 resulted in retarded in vivo pollen tube growth (Bosch and Hepler, 2006).…”