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 malonyl-CoA to generate triketide and tetraketide α-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.
Formins are well-known regulators that participate in the organization of the actin cytoskeleton in organisms.The Arabidopsis thaliana L.genome encodes 21 formins,which can be divided into two distinct subfamilies.However,type II formins have to date been less well characterized.Here,we cloned a type II formin,AtFH16,and characterized its biochemical activities on actin and microtubule dynamics.The results show that the FH1FH2 structure of AtFH16 cannot nucleate actin polymerization effciently,but can bind and bundle microflaments.AtFH16 FH1FH2 is also able to bind and bundle microtubules,and preferentially binds microtubules over microflaments in vitro.In addition,AtFH16 FH1FH2 co-localizes with microtubules in onion epidermal cells,indicating a higher binding affnity of AtFH16 FH1FH2 for microtubules rather than microflaments in vivo.In conclusion,AtFH16 is able to interact with both microflaments and microtubules,suggesting that AtFH16 probably functions as a bifunctional protein,and may thus participate in plant cellular processes.
