Tetrad pollen formation in quartet mutants of Arabidopsis thaliana is associated with persistence of pectic polysaccharides of the pollen mother cell wall

Abstract

SummaryThe quartet (qrt) mutants of Arabidopsis thaliana produce tetrad pollen in which microspores fail to separate during pollen development. Because the amount of callose deposition between microspores is correlated with tetrad pollen formation in other species, and because pectin is implicated as playing a role in cell adhesion, these cell-wall components in wild-type and mutant anthers were visualized by immunofluorescence microscopy at different stages of microsporogenesis. In wild-type, callose was detected around the pollen mother cell at the onset of meiosis and around the microspores during the tetrad stage. Microspores were released into the anther locule at the stage where callose was no longer detected. Deposition and degradation of callose during tetrad pollen formation in qrt1 and qrt2 mutants were indistinguishable from those in wild-type. Enzymatic removal of callose from wild-type microspores at the tetrad stage did not release the microspores, suggesting that callose removal is not sufficient to disperse the microspores in wild-type. Pectic components were detected in the primary wall of the pollen mother cell. This wall surrounded the callosic wall around the pollen mother cell and the microspores during the tetrad stage. In wild-type, pectic components of this wall were no longer detectable at the time of microspore release. However, in qrt1 and qrt2 mutants, pectic components of this wall persisted after callose degradation. This result suggests that failure of pectin degradation in the pollen mother cell wall is associated with tetrad pollen formation in qrt mutants, and indicates that QRT1 and QRT2 may be required for cell type-specific pectin degradation to separate microspores.

PECTIN METHYLESTERASE48 Is Involved in Arabidopsis Pollen Grain Germination

“…In many species, such as tobacco (Li et al, 1995), Arabidopsis (Van Aelst and Van Went, 1992; Rhee and Somerville, 1998), Lilium hybrida (Aouali et al, 2001), Euphorbia peplus (Suárez-Cervera et al, 2002), Zygophyllum fabago (Castells et al, 2003), and Larix decidua (Rafinska et al, 2014), the intine of mature pollen grains is mostly composed of weakly methylesterified HG or a mix of highly and weakly methylesterified HGs, the latter being more abundant. The almost absent labeling of weakly methylesterified HG with John Innes Monoclonal5 at the pollen mother cell and tetrad stages (Rhee and Somerville, 1998) but its strong detection in the intine at the late microspore stage and mature dry Arabidopsis pollen grains (Van Aelst and Van Went, 1992; Rhee and Somerville, 1998) indicate an early action of PMEs during pollen formation and maturation. HG polymers are synthesized in the Golgi apparatus and may be secreted under a highly methylesterified form and then processed in the cell wall by PMEs (Zhang and Staehelin, 1992;Caffall and Mohnen, 2009;Harholt et al, 2010).…”

Global analysis of gene expression in flower buds of Ms-cd1 Brassica oleracea conferring male sterility by using an Arabidopsis microarray

“…It initiates with the emergence of the stamen primordia in the third whorl of the floral meristem and concludes with the release of pollen grains at dehiscence (Goldberg et al 1993). After meiosis, tetrads are enclosed in a thick shell composed of a callose wall with components of b-1,3-glucan and a pollen mother cell (PMC) wall with the components cellulose, hemicelluloses and pectins (Rhee and Somerville 1998). At a critical developmental point (Arabidopsis flower development stage 10-early stage 11 (Ma 2005), the tetrad wall is degraded by the enzymes secreted by the tapetal cells (Hird et al 1993).…”

Targeted Modification of Homogalacturonan by Transgenic Expression of a Fungal Polygalacturonase Alters Plant Growth

“…Cells of emb30 mutants are larger than those of the wild type and do not adhere well to each other; the seeds are impaired in the control of cell division, expansion, and polarity and do not develop as wild type (Shevell et al, 2000). The Arabidopsis quartet mutants have microspores that fail to separate during pollen development as a result of the persistence of pectin in the pollen mother cell wall (Rhee and Somerville, 1998). The Arabidopsis mur1 mutation, leading to a deficiency in fucosyl residues, affects RG-II, reducing its capacity to dimerize through the formation of boron diester cross-links, and this disrupts plant growth ).…”