Cell wall Glycine-rich Protein2 is involved in tapetal differentiation and pollen maturation
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REGULAR PAPER — PHYSIOLOGY/BIOCHEMISTRY/MOLECULAR AND CELLULAR BIOLOGY
Cell wall Glycine-rich Protein2 is involved in tapetal differentiation and pollen maturation Naomi Takebe1 · Atsuko Nakamura1 · Tomomi Watanabe1 · Aya Miyashita1 · Shinobu Satoh1 · Hiroaki Iwai1 Received: 18 March 2020 / Accepted: 1 September 2020 © The Botanical Society of Japan 2020
Abstract The tapetum plays important roles in anther development by providing materials for pollen-wall formation and nutrients for pollen development. Here, we report the characterization of a male-sterile mutant of glycine-rich protein 2 (OsGRP2), which exhibits irregular cell division and dysfunction of the tapetum. GRP is a cellwall structural protein present in the cell walls of diverse plant species, but its function is unclear in pollen development. We found that few GRP genes are expressed in rice and thus focused on one highly expressed gene, OsGRP2. The tapetal cell walls of an OsGRP2 mutant did not thicken at the pollen mothercell stage, as a result, pollen maturation and fertility rate decreased. High OsGRP2 expression was detected in male-floral organs, and OsGRP2 was distributed in the tapetum. OsGRP2 participated in establishment of the cellwall network during early tapetum development. In conclusion, our results indicate that OsGRP2 plays important roles in the differentiation and function of the tapetum. Keywords Cell wall · Glycine-rich protein · Male sterility · Oryza sativa · Pollen · Tapetum
Introduction In higher plants, the anther, a bilaterally symmetrical structure with four lobes, yields mature pollen grains (Goldberg et al. 1993). Cells divide and differentiate within each lobe to form four distinct somatic cell layers, which are designated from the exterior to the interior as the epidermis, endothecium, middle layer, and tapetum (Goldberg et al. 1993; Sanders et al. 1999). Participation of both the developing haploid gametophytic cells and the accessory diploid sporophytic cells is necessary for the production of gametes in plants. The tapetum, which arises from secondary parietal cells and connective tissues, surrounds the L2-derived, Naomi Takebe and Hiroaki Iwai contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10265-020-01223-x) contains supplementary material, which is available to authorized users. * Hiroaki Iwai [email protected] 1
Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Tsukuba 305‑8572, Japan
developing reproductive cells (Goldberg et al. 1993) The tapetum plays an important role in pollen development by contributing to microspore release, nutrition, pollen‐wall synthesis, and sporopollenin deposition (Mariani et al. 1990; Pacini et al. 1985; Piffanelli et al. 1998; Stieglitz and Stern 1973). Several genes essential for tapetal development and function have been identified in Arabidopsis. SPOROCYTELESS/NOZZLE (SPL/NZZ), BARELY ANY MERISTEM 1 (BAM1) and BAM2, EXCESS MICROSPOROCYTES 1/ EXT
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