PERSISTENT TAPETAL CELL1Encodes a PHD-Finger Protein That Is Required for Tapetal Cell Death and Pollen Development in Rice      

Abstract

In higher plants, timely degradation of tapetal cells, the innermost sporophytic cells of the anther wall layer, is a prerequisite for the development of viable pollen grains. However, relatively little is known about the mechanism underlying programmed tapetal cell development and degradation. Here, we report a key regulator in monocot rice (Oryza sativa), PERSISTANT TAPETAL CELL1 (PTC1), which controls programmed tapetal development and functional pollen formation. The evolutionary significance of PTC1 was revealed by partial genetic complementation of the homologous mutation MALE STERILITY1 (MS1) in the dicot Arabidopsis (Arabidopsis thaliana). PTC1 encodes a PHD-finger (for plant homeodomain) protein, which is expressed specifically in tapetal cells and microspores during anther development in stages 8 and 9, when the wild-type tapetal cells initiate a typical apoptosis-like cell death. Even though ptc1 mutants show phenotypic similarity to ms1 in a lack of tapetal DNA fragmentation, delayed tapetal degeneration, as well as abnormal pollen wall formation and aborted microspore development, the ptc1 mutant displays a previously unreported phenotype of uncontrolled tapetal proliferation and subsequent commencement of necrosis-like tapetal death. Microarray analysis indicated that 2,417 tapetum-and microspore-expressed genes, which are principally associated with tapetal development, degeneration, and pollen wall formation, had changed expression in ptc1 anthers. Moreover, the regulatory role of PTC1 in anther development was revealed by comparison with MS1 and other rice anther developmental regulators. These findings suggest a diversified and conserved switch of PTC1/MS1 in regulating programmed male reproductive development in both dicots and monocots, which provides new insights in plant anther development.

Two ATP Binding Cassette G (ABCG) Transporters, OsABCG26 and OsABCG15, Collaboratively Regulate Rice Male Reproduction

“…2P), in which the bulged structure in osabcg26 exine surface was obscure at stage 13, indicating possible overdeposition of lipidic precursors onto the pollen exine surface. Consistent with the role of characteristic orbicules/Ubisch bodies in exporting tapetumsynthesized sporopollenin precursors across the hydrophilic cell wall to the anther locule (Huysmans et al,1998;Li et al, 2010Li et al, , 2011, we observed the regular shape of orbicules containing electron-dense lipidic precursors along the tangential inner surface of wildtype tapetal cells (Fig. 3, I and O); in contrast, the morphological structure of osabcg26 orbicules/Ubisch bodies was abnormal, which contained more electrondense lipidic substances (Fig.…”

“…Moreover, we observed that the mutation of OsABCG26 also affected the expression of three previously reported program cell death regulators, such as TDR (Li et al, 2006), GAMYB (Aya et al, 2009), and PERSISTENT TAPETAL CELL1 (PTC1; Li et al, 2011). The expression levels of TDR and GAMYB were decreased in osabcg26, whereas those of PTC1 were fluctuating in osabcg26 (Fig.…”

EAT1 promotes tapetal cell death by regulating aspartic proteases during male reproductive development in rice

“…Unlike the expanded tapetal cells in gamyb, udt1 and tdr 9-11 , or necrosis in ptc1 tapetum 12 , eat1-1 displays a delay in tapetal PCD without cell enlargement or necrosis-like phenotypes (Fig. 1a-l and Fig 2 and Supplementary Figs S2 and 3b).…”

“…Mutant identification, plant growth, map-based cloning, phenotypic characterizations and gene expression analyses were performed using methods from our previous reports 7,11,12 . Anther staging is defined by Zhang and Wilson 45 .…”

“…Several transcriptional regulators have been reported to be associated with tapetal degeneration, including Arabidopsis MYB33/MYB65 4 , DYSFUNCTIONAL TAPETUM1 (DYT1) 5 , DEFECTIVE IN TAPETAL DEVELOPMENT AND FUNCTION1 (TDF1) 6 , ABORTED MICROSPORE (AMS) 7 , MALE STERILITY1 8 , rice GAMYB 9 , UNDEVELOPED TAPETUM1 10 , TAPETUM DEGENERATION RETARDATION (TDR) 11 , PERSISTENT TAPETAL CELL 1 (PTC1) 12 , and APOPTOSIS INHIBITOR5 (API5) 13 . However, mechanisms by which these regulators regulate tapetal PCD remain unclear.…”