Tapetum Degeneration Retardation is Critical for Aliphatic Metabolism and Gene Regulation during Rice Pollen Development

Abstract

As a complex wall system in flowering plants, the pollen outer wall mainly contains aliphatic sporopollenin; however, the mechanism for synthesizing these lipidic precursors during pollen development remains less well understood. Here, we report on the function of the rice tapetum-expressing TDR (Tapetum Degeneration Retardation) gene in aliphatic metabolism and its regulatory role during rice pollen development. The observations of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses suggested that pollen wall formation was significantly altered in the tdr mutant. The contents of aliphatic compositions of anther were greatly changed in the tdr mutant revealed by GC-MS (gas chromatography-mass spectrometry) testing, particularly less accumulated in fatty acids, primary alcohols, alkanes and alkenes, and an abnormal increase in secondary alcohols with carbon lengths from C29 to C35 in tdr. Microarray data revealed that a group of genes putatively involved in lipid transport and metabolism were significantly altered in the tdr mutant, indicating the critical role of TDR in the formation of the pollen wall. Also, a wide range of genes (236 in total-154 up-regulated and 82 down-regulated) exhibited statistically significant expressional differences between wild-type and tdr. In addition to its function in promoting tapetum PCD, TDR possibly plays crucial regulatory roles in several basic biological processes during rice pollen development.

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

“…UDT1 and TDR are bHLH transcription factors, and GAMYB encodes a MYB domain transcription factor. Tapetal cells in gamyb, tdr, and udt1 display delayed degeneration and abnormal enlargement, occupying the locule space and causing microspore abortion and defective pollen exine (Kaneko et al, 2004;Jung et al, 2005;Li et al, 2006;Zhang et al, 2008;Liu et al, 2010). Furthermore, no expression alteration of PTC1 was observed in tdr and udt1 (Jung et al, 2005;Zhang et al, 2008), while significant reduction of PTC1 was seen in gamyb-2 (Aya et al, 2009), suggesting that PTC1 may act downstream of GAMYB in rice anther development and, consistent with this, that PTC1 is expressed after GAMYB (Fig.…”

“…11). Conversely, PTC1 was shown to have reduced expression in gamyb-2 mutants (Aya et al, 2009) but no obvious expression change in udt1 and tdr (Jung et al, 2005;Zhang et al, 2008).…”

“…To aid characterization of the regulatory role of PTC1, the expression profiles of the gamyb-2, udt1, and tdr mutants were compared (Jung et al, 2005;Zhang et al, 2008;Aya et al, 2009). We observed that 40.3% (93 of 231) of the genes changing in tdr, 10.5% (128 of 1,225) in udt1, and 24.2% (210 of 870) in gamyb-2 had expression changes in ptc1 (Supplemental Data Set S3).…”

“…Observation of anther development by semithin sections and transmission electron microscopy were performed as described by Li et al (2006). SEM was performed as described by Zhang et al (2008).…”

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

“…Up to date, some tapetum-expressed proteins, such as cytochrome P450s (CYP450s; Li et al, 2010;Yang et al, 2014), fatty acyl carrier protein (ACP) reductase (Shi et al, 2011), ABCG transporters (Niu et al, 2013a;Qin et al, 2013;Zhu et al, 2013;Wu et al, 2014), LTPs , and basic helix-loophelix (bHLH) transcription factors (Li et al, 2006;Zhang et al, 2008;Niu et al, 2013b), have been identified to be involved in anther cuticle and pollen exine development in rice. CYP704B2 functions as a v-hydroxylase in producing v-hydroxylated fatty acids with 16 and 18 carbon chains as the common precursors of two biopolymers: sporopollenin and cutin (Li et al, 2010).…”