Rice No Pollen 1 (NP1) is required for anther cuticle formation and pollen exine patterning

Abstract

Angiosperm male reproductive organs (anthers and pollen grains) have complex and interesting morphological features, but mechanisms that underlie their patterning are poorly understood. Here we report the isolation and characterization of a male sterile mutant of No Pollen 1 (NP1) in rice (Oryza sativa). The np1-4 mutant exhibited smaller anthers with a smooth cuticle surface, abnormal Ubisch bodies, and aborted pollen grains covered with irregular exine. Wild-type exine has two continuous layers; but np1-4 exine showed a discontinuous structure with large granules of varying size. Chemical analysis revealed reduction in most of the cutin monomers in np1-4 anthers, and less cuticular wax. Map-based cloning suggested that NP1 encodes a putative glucose-methanol-choline oxidoreductase; and expression analyses found NP1 preferentially expressed in the tapetal layer from stage 8 to stage 10 of anther development. Additionally, the expression of several genes involved in biosynthesis and in the transport of lipid monomers of sporopollenin and cutin was decreased in np1-4 mutant anthers. Taken together, these observations suggest that NP1 is required for anther cuticle formation, and for patterning of Ubisch bodies and the exine. We propose that products of NP1 are likely important metabolites in the development of Ubisch bodies and pollen exine, necessary for polymerization, assembly, or both.

DEGENERATED PANICLE AND PARTIAL STERILITY 1 (DPS1) encodes a cystathionine β‐synthase domain containing protein required for anther cuticle and panicle development in rice

“…As many male sterility mutants showed defective development of the anther cuticle (Liu et al ., ; Men et al ., ), we used SEM to observe the anther cuticle development. Notably, the well‐developed three‐dimensional cuticular nano‐ridges on the epidermis of WT anthers (Fig.…”

“…). These are typical and often‐reported phenotypes for male sterility in rice (Li et al ., ; Shi et al ., ; Zhao et al ., ; Liu et al ., ; Men et al ., ). DPS1 belongs to the CBS domain protein family, and none of its orthologues in other species has been characterized.…”

TDR INTERACTING PROTEIN 3, encoding a PHD‐finger transcription factor, regulates Ubisch bodies and pollen wall formation in rice

“…The abnormal structure of Ubisch bodies may affect the assembly and deposition of sporopollenin on the primexine leading to a lack of pollen exine. This mutant phenotype is reminiscent of the phenotypes of np1 in rice (Liu et al ., ). Ubisch body kernels of the np1‐4 mutant were surrounded by abundant electron‐dense materials, leaving only a small hole on one side.…”

“…Ubisch body kernels of the np1‐4 mutant were surrounded by abundant electron‐dense materials, leaving only a small hole on one side. This mutation was caused by NP1 , a putative glucose‐methanol‐choline (GMC) oxidoreductase, and was likely to be involved in the production of lipidic molecules required for polymerization or assembly (or both) of sporopollenin precursors (Liu et al ., ). Furthermore, smaller Ubisch bodies have been observed in ptc1 with the reduction of both the electron‐opaque central region and the surrounding electron‐dense particles (Li et al ., 2011a).…”

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

“…In both Arabidopsis and rice, mutants of most anther‐specific lipid and phenolic metabolism‐associated genes are partially or completely male sterile (Shi et al ). A growing body of evidence indicates that some of these key enzymes are required to not only provide structural chemicals, but also to supply patterning chemicals to assemble these two protective layers (Dobritsa et al ; Kim et al ; Liu et al ). Arabidopsis PKSB/LAP5 encodes a polyketide synthase and has a partially redundant function with PKSA/LAP6 in the generation of sporopollenin monomers.…”