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Gibberellin Regulates Pollen Viability and Pollen Tube Growth in Rice^[W]

^a Bioscience and Biotechnology Center, Nagoya University, Chikusa, Nagoya 464-8601, Japan
^b Japan Society for the Promotion of Science, Chiyoda, Tokyo 102-8472, Japan
^c Honda Research Institute Japan, Kazusa-Kamatari, Kisarazu-shi, Chiba 292-0818, Japan
^d Graduate School of Life Science, Tohoku University, Aoba, Sendai 980-8577, Japan

² Address correspondence to makoto{at}nuagr1.agr.nagoya-u.ac.jp.

Gibberellins (GAs) play many biological roles in higher plants. We collected and performed genetic analysis on rice (Oryza sativa) GA-related mutants, including GA-deficient and GA-insensitive mutants. Genetic analysis of the mutants revealed that rice GA-deficient mutations are not transmitted as Mendelian traits to the next generation following self-pollination of F1 heterozygous plants, although GA-insensitive mutations are transmitted normally. To understand these differences in transmission, we examined the effect of GA on microsporogenesis and pollen tube elongation in rice using new GA-deficient and GA-insensitive mutants that produce semifertile flowers. Phenotypic analysis revealed that the GA-deficient mutant reduced pollen elongation1 is defective in pollen tube elongation, resulting in a low fertilization frequency, whereas the GA-insensitive semidominant mutant Slr1-d3 is mainly defective in viable pollen production. Quantitative RT-PCR revealed that GA biosynthesis genes tested whose mutations are transmitted to the next generation at a lower frequency are preferentially expressed after meiosis during pollen development, but expression is absent or very low before the meiosis stage, whereas GA signal-related genes are actively expressed before meiosis. Based on these observations, we predict that the transmission of GA-signaling genes occurs in a sporophytic manner, since the protein products and/or mRNA transcripts of these genes may be introduced into pollen-carrying mutant alleles, whereas GA synthesis genes are transmitted in a gametophytic manner, since these genes are preferentially expressed after meiosis.