Arabidopsis RPG1 is important for primexine deposition and functions redundantly with RPG2 for plant fertility at the late reproductive stage

Abstract

Arabidopsis Ruptured Pollen Grain-1 (RPG1/Sweet8) is a member of the MtN3/saliva protein family that functions as a sugar transporter. The rpg1 mutant shows defective exine pattern formation. In this study, transmission electron microscopy (TEM) observations showed that much less primexine was deposited in rpg1 tetrads. Furthermore, microspore membrane undulation was abnormal, and sporopollenin accumulation was also defective. This suggests that a reduced primexine deposition in rpg1 leads to abnormal membrane undulation that affects exine pattern formation. Chemical staining revealed thinning of the callose wall of rpg1, as well as significantly reduced expression of Callose synthase-5 (CalS5) in rpg1. The fertility of the rpg1 mutant could be partly restored at late reproductive stages, potentially complemented in part by RPG2, another member of the MtN3/saliva family, which is expressed in the anther during microsporogenesis. The double mutant, rpg1rpg2, was almost sterile and was not restored during late reproduction. These results suggest that RPG1 and RPG2 are involved in primexine deposition and therefore pollen wall pattern formation.

A Rice Ca2+ Binding Protein Is Required for Tapetum Function and Pollen Formation

“…Several genes have been identified that influence primexine formation in Arabidopsis (Paxson-Sowders et al, 2001;Ariizumi et al, 2004;Chang et al, 2012;Sun et al, 2013), while no gene has been identified in rice. In this study, we identified the ortholog of Arabidopsis DEX1 in rice, which shares a similar function with Arabidopsis DEX1 in regulating primexine formation and male fertility (Paxson-Sowders et al, 2001).…”

“…Evidence for this comes from reported primexine defective mutants, such as dex1, nef, hkm, and rpg1, whose heterozygous mutants showed normal primexine formation (Paxson-Sowders et al, 2001;Ariizumi et al, 2004;Chang et al, 2012;Sun et al, 2013). Tapetal cell death is of vital importance for exine formation (Sorensen et al,2003;Li et al, 2006;Zhang et al, 2008;Aya et al, 2009;Xu et al, 2010;Niu et al, 2013;Ji et al,2013).…”

“…The differentiation of the innermost tapetal cell layer is crucial for pollen formation (Kelliher and Walbot, 2012;Fu et al, 2014;Zhang and Yang, 2014). After the formation of tapetal cells, subsequent tapetal cell and callose degradation, as well as primexine formation, are vital for pollen development (Ma, 2005;Li et al, 2006;Wu and Cheun, 2000;Paxson-Sowders et al, 2001;Ariizumi et al, 2004;Li et al, 2011a;Chang et al, 2012;Ji et al, 2013;Niu et al, 2013;Sun et al, 2013).…”

“…Mutants defective in callose degradation in rice also have defects in exine formation and pollen development (Wan et al, 2011). In Arabidopsis (Arabidopsis thaliana), Defective in Exine Formation1 (DEX1), No Exine Formation1 (NEF1), Ruptured Pollen Grain1 (RPG1), Ruptured Pollen Grain2 (RPG2), and No Primexine and Plasma Membrane Undulation (NPU) are required for primexine formation, and their corresponding mutants are defective in exine formation (Paxson-Sowders et al, 2001;Ariizumi et al, 2004;Chang et al, 2012;Sun et al, 2013). After the formation of the primexine, sporopollenin was synthesized in the tapetum and transported to the microspore.…”

KNS4/UPEX1: A Type II Arabinogalactan β-(1,3)-Galactosyltransferase Required for Pollen Exine Development

“…Mutations in CALLOSE SYNTHASE5 (CALS5)/GLUCAN SYNTHASE LIKE2 (GSL2) cause a severe defect in exine development despite normal deposition of primexine (Dong et al, 2005;Nishikawa et al, 2005). Furthermore, RUPTURED POLLEN GRAIN1 (RPG1), NO PRIMEXINE AND PLASMA MEMBRANE UNDULATION (NPU), and EXINE FORMATION DEFECT (EFD) are required for CALS5/GSL2 expression, primexine deposition, and plasma membrane undulation (Guan et al, 2008;Chang et al, 2012;Sun et al, 2013;Hu et al, 2014). Mutations in these genes almost completely abolish the structure of exine and often affect the viability of pollen grains.…”