The polyketide synthase OsPKS2 is essential for pollen exine and Ubisch body patterning in rice

Abstract

Lipid and phenolic metabolism are important for pollen exine formation. In Arabidopsis, polyketide synthases (PKSs) are essential for both sporopollenin biosynthesis and exine formation. Here, we characterized the role of a polyketide synthase (OsPKS2) in male reproduction of rice (Oryza sativa). Recombinant OsPKS2 catalyzed the condensation of fatty acyl-CoA with malonylCoA to generate triketide and tetraketide a-pyrones, the main components of pollen exine. Indeed, the ospks2 mutant had defective exine patterning and was male sterile. However, the mutant showed no significant reduction in sporopollenin accumulation. Compared with the WT (wild type), ospks2 displayed unconfined and amorphous tectum and nexine layers in the exine, and less organized Ubisch bodies. Like the pksb/lap5 mutant of the Arabidopsis ortholog, ospks2 showed broad alterations in the profiles of anther-related phenolic compounds. However, unlike pksb/lap5, in which most detected phenolics were substantially decreased, ospks2 accumulated higher levels of phenolics. Based on these results and our observation that OsPKS2 is unable to fully restore the exine defects in the pksb/lap5, we propose that PKS proteins have functionally diversified during evolution. Collectively, our results suggest that PKSs represent a conserved and diversified biochemical pathway for anther and pollen development in higher plants.

PERSISTENT TAPETAL CELL2 Is Required for Normal Tapetal Programmed Cell Death and Pollen Wall Patterning

“…Loss of function of these genes often leads to defective pollen wall formation, indicating the important role of lipid metabolism on pollen wall formation. Reported genes involved in phenolic metabolism include Oryza sativa Polyketide Synthase1 (OsPKS1; Wang et al, 2013;Zou et al, 2017), OsPKS2 (Wang et al, 2013;Zhu et al, 2017), No Pollen1 (NP1; Chang et al, 2016;Liu et al, 2017), and DPW2 (Xu et al, 2017). Mutants of these genes also display abnormal pollen wall patterning, suggesting that cross linking between aromatic and aliphatic monomers is also important for pollen wall formation.…”

The Tapetal Major Facilitator NPF2.8 Is Required for Accumulation of Flavonol Glycosides on the Pollen Surface in Arabidopsis thaliana

“…Database searches failed to identify any FST1 transporter orthologue in saffron, although this might also be due to low sequence coverage of this clade in the current datasets available for this species. Flavonol and flavone glycosides were also reported from rice anthers (Zhu et al, 2017) and several MFS-type transporters with roughly 40% sequence identity to FST1 can be found in rice and many other monocots. Their identity is higher than the identity of FST1 to the Arabidopsis NPF2.9, NPF2.10, and NPF 2.11 glucosinolate transporters.…”

A Silent Exonic Mutation in a Rice Integrin-α FG-GAP Repeat-Containing Gene Causes Male-Sterility by Affecting mRNA Splicing

“…To explore the role of PL1 in anther cuticle, tapetum and pollen development, we analyzed expression profiles of several known genes, which were critical for anther and pollen development, in WT and pl1 spikelets with anthers from stages 4 to 11 by qRT-PCR. We first monitored CYP703A3 [24], OsACOS12 [26,27], OsPKS2 [28,29] and OsTKPR1 [32], which are required for pollen exine formation and lipid metabolism in tapetal cells. Our analysis showed that the expression levels of these genes were decreased in pl1 (Figure 8A-D).…”

“…The outer pollen wall, exine, is mainly composed of sporopollenin [5]. In rice, several genes involved in sporopollenin precursors synthesis and shipping have been found, such as CYP703A3 [24], CYP704B2 [25], Acyl-CoA Synthetase 12 (OsACOS12) [26,27], Polyketide synthase 1/2 (OsPKS1/2) [28][29][30][31], Tetraketide α-pyrone reductase 1 (OsTKPR1) [31,32], ATP Binding Cassette G 15 (OsABCG15) [16,33,34], and OsC4/6 [35]. Among them, CYP703A3, CYP704B2, OsACOS12, OsPKS1/2 and OsTKPR1 may form a sporopollenin metabolon similar to their orthologues in Arabidopsis [5,8,15,31,32,36].…”