Disease outbreaks devastate Pyropia aquaculture farms every year. The three most common and serious diseases are Olpidiopsis‐blight and red‐rot disease caused by oomycete pathogens and green‐spot disease caused by the PyroV1 virus. We hypothesized that a basic genetic profile of molecular defenses will be revealed by comparing and analyzing the genetic response of Pyropia tenera against the above three pathogens. RNAs isolated from infected thalli were hybridized onto an oligochip containing 15,115 primers designed from P. tenera expressed sequence tags (EST)s. Microarray profiles of the three diseases were compared and interpreted together with histochemical observation. Massive amounts of reactive oxygen species accumulated in P. tenera cells exposed to oomycete pathogens. Heat shock genes and serine proteases were the most highly up‐regulated genes in all infection experiments. Genes involved in RNA metabolism, ribosomal proteins and antioxidant metabolism were also highly up‐regulated. Genetic profiles of P. tenera in response to pathogens were most similar between the two biotrophic pathogens, Olpidiopsis pyropiae and PyroV1 virus. A group of plant resistance genes were specifically regulated against each pathogen. Our results suggested that disease response in P. tenera consists of a general constitutive defense and a genetic toolkit against specific pathogens.

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Red algal fertilization is unusual and offers a different model to the mechanism of intracellular transport of nuclei and polyspermy blocking. A female carpogonium (egg) undergoes plasmogamy with many spermatia (sperm) simultaneously at the receptive structure, trichogyne, which often contains numerous male nuclei. The pattern of selective transport of a male nucleus to the female nucleus, located in the cell body of the carpogonium, remain largely unknown. We tracked the movement of spermatial nuclei and cell organelles in the trichogyne after plasmogamy using time-lapse videography and fluorescent probes. The fertilization process of Bostrychia moritziana is composed of five distinctive stages: 1) gamete-gamete binding; 2) mitosis in the attached spermatia; 3) formation of a fertilization channel; 4) migration of spermatial nuclei into the trichogyne; and 5) cutting off of the trichogyne cytoplasm from the rest of the cell after karyogamy. Our results showed that actin microfilaments were involved in the above steps of fertilization, microtubules are involved only in spermatial mitosis. Time-lapse videography showed that the first ("primary") nucleus which entered to trichogyne moved quickly to the base of carpogonium and fused with the female nucleus. The transport of the primary male nucleus to the egg nucleus was complete before its second nucleus migrated into the trichogyne. Male nuclei from other spermatia stopped directional movement soon after the first one entered the carpogonial base and oscillated near where they entered trichogyne. The cytoplasm of the trichogyne was cut off at a narrow neck connecting the trichogyne and carpogonial base after gamete nuclear fusion but gamete binding and plasmogamy continued on the trichogyne. Spermatial organelles, including mitochondria, entered the trichogyne together with the nuclei but did not show any directional movement and remained close to where they entered. These results suggest that polyspermy blocking in B. moritziana is achieved by the selective and rapid transport of the first nucleus entered trichogyne and the rupture of the trichogyne after gamete karyogamy.