Editors' ChoicePlant biology

High-Temperature Mating Success

Sci. Signal.  17 Sep 2013:
Vol. 6, Issue 293, pp. ec222
DOI: 10.1126/scisignal.2004727

When a pollen grain lands on the stigma of a compatible pistil, the pollen grain sends a cytoplasmic extension through the “style,” the stalk of the pistil, to carry sperm from the pollen grain to ovules inside the pistil. Pollen tube growth and fertilization are sensitive to temperature fluctuations. Endo et al. report that signaling by the CLV3/ESR-related peptide CLE45 and its receptors ensures adequate fertilization at high temperature in Arabidopsis thaliana. CLE45 was expressed in the stigma at 22°C, but its expression expanded into the style at 30°C. Reducing CLE45 expression by RNA interference (RNAi) caused no phenotype in plants grown at 22°C but reduced the number of seeds in fruits and the length of fruits when the plants were shifted to 30°C. Known CLE peptide receptors are leucine-rich repeat receptor-like kinases (LRR-RLKs), and the authors tested LRR-RLKs that are expressed in pollen for their ability to mediate the effects of CLE45 on pollen tube growth. Application of synthetic CLE45 increased the length of pollen tubes in an in vitro pollen tube assay, but plants carrying inactivating mutations in the genes encoding the LRR-RLKs STERILITY-REGULATING KINASE MEMBERs 1 and 2 (SKM1 and SKM2) were insensitive to CLE45 application. Expressing a transgene encoding a kinase-dead version of SKM1 in skm1 mutants caused a high-temperature phenotype similar to CLE45 RNAi plants. Genetic experiments were consistent with CLE45 functioning in the pistil and SKM1 and SKM2 in the pollen, and immunoprecipitation experiments using tagged versions of recombinant SKM1 produced in cultured cells and synthetic CLE45 indicated direct binding between these molecules. Mitochondrial activity in pollen is important for sustaining pollen tube growth and for subsequent fertilization events and has been reported to decrease in other plant species at high temperature. Using a colorimetric assay for mitochondrial activity, the authors found that CLE45-SKM signaling prolonged the activity of pollen mitochondria at 30°C. Although CLE45 signaling promoted pollen tube growth in vitro, its role in vivo appeared specific to promoting the pollen-ovule interactions that are required for fertilization after tube growth. These activities are consistent with the finding that CLE45-SKM signaling mediates pollen-pistil interactions to maintain mitochondrial activity at high temperature and thus ensures adequate fertilization.

S. Endo, H. Shinohara, Y. Matsubayashi, H. Fukuda, A novel pollen-pistil interaction conferring high-temperature tolerance during reproduction via CLE45 signaling. Curr. Biol. 23, 1670–1676 (2013). [PubMed]

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