Comparison of fertile and sterile male gametogenesis in Cryptomeria japonica D. Don

Cryptomeria japonica D. Don is one of the most important conifers for forestry; however, the pollinosis caused by this species is the most prevalent allergy in Japan. Male-sterile mutants have attracted attention as countermeasures to prevent pollen dispersion. Histological and transcriptomic analyses were conducted on one of the C. japonica male-sterile mutant lines, Toyama 1. Histological examination of pollen development revealed that the lamellar structure of the endexine was not observed in pollen of Toyama 1 and that the microspore was disrupted during the tetrad stage. To determine the mechanism causing male sterility in C. japonica , we analyzed gene expression in normal and sterile male strobili derived from the progeny of Toyama 1. A microarray of 22,882 low-redundancy sequences was designed from C. japonica cDNAs for this experiment. Microarray analysis revealed that the expression pattern of genes in male strobili during pollen development was very similar between fertile and male-sterile individuals. We confirmed 32 genes that were expressed at a lower level in sterile male strobili than in fertile ones at the stage when the disrupted microspores were observed in the sterile mutant. Nine of these 32 genes showed similarity to those involved in carbohydrate metabolic process, phosphorylation, and transmembrane transport. Other genes showed similarity to those involved in regulation of transcription, signal transduction, protein modification, and transport of ions and amino acids. These results suggest that the gene responsible for the Toyama 1 mutant may be involved in the network regulating pollen wall formation.