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A Novel Pollen-Pistil Interaction Conferring High-Temperature Tolerance during Reproduction via CLE45 Signaling.

By August 13, 2013No Comments
pm1[Epub ahead of print]

A Novel Pollen-Pistil Interaction Conferring High-Temperature Tolerance during Reproduction via CLE45 Signaling.

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Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan. Electronic address: satoshi@biol.s.u-tokyo.ac.jp.

Abstract

Flowering plants in the reproductive stage are particularly vulnerable to ambient temperature fluctuations [1-6]. Nevertheless, they maintain seed production under certain levels of exposure to temperature change. The mechanisms underlying this temperature tolerance are largely unknown. Using an in vitro Arabidopsis pollen tube culture, we found that a synthetic CLV3/ESR-related peptide, CLE45, prolonged pollen tube growth. A subsequent screen of Arabidopsis mutants of leucine-rich repeat receptor-like kinase genes identified two candidate receptors for CLE45 peptide, STERILITY-REGULATING KINASE MEMBER1 (SKM1) and SKM2. The double loss-of-function mutant was insensitive to CLE45 peptide in terms of pollen tube growth in vitro. The SKM1 protein actually interacted with CLE45 peptide. CLE45 was preferentially expressed in the stigma in the pistil at 22°C, but upon temperature shift to 30°C, its expression expanded to the transmitting tract, along which pollen tubes elongated. In contrast, both SKM1 and SKM2 were expressed in pollen. Disturbance of CLE45-SKM1/SKM2 signaling transduction by either RNAi suppression of CLE45 expression or introduction of a kinase-dead version of SKM1 into skm1 plants reduced seed production at 30°C, but not at 22°C. Taken together with the finding that CLE45 peptide application alleviated mitochondrial decay during the in vitro pollen tube culture, these results strongly suggest that the pollen-pistil interaction via the CLE45-SKM1/SKM2 signaling pathway sustains pollen performance under higher temperatures, leading to successful seed production.
Copyright © 2013 Elsevier Ltd. All rights reserved.
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23910659

 

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Figure 1. Identification and Characterization of a Novel CLE Gene in Regulating Pollen Performance and Seed Production under Relatively High Temperature(A–C) Novel CLE peptide activities in promoting WT Arabidopsis pollen tube growth in vitro. Distributions of pollen tubes of the indicated tube lengths were measured in the presence (solid lines with filled circles) or absence (dashed lines with filled squares) of synthetic CLE45 (A), CLE43 (B), or CLV3 (C) peptide. Pollen grains of WT Arabidopsis were cultured for 20 hr at 30°C. Each data set represents the mean of at least four independent cultures ± SD; 30–40 pollen tubes were measured in each culture.(D–H) CLE45 expression in pistils ofArabidopsis flowers. GUS expression in pCLE45::GUS transgenic Arabidopsis flowers was examined before (D and E) and after (F–H) anthesis. Pistils of 7-week-old plants without (D and F) or with (E, G, and H) incubation for 24 hr at 30°C are shown. A dissected transmitting tract is shown in (H). Scale bars represent 200 μm.(I–M) Functional analysis ofCLE45 in Arabidopsis. Numbers of developing seeds (I and J) and fruit lengths (K and L) were measured in WT, RNAi-control (light gray column), and CLE45-RNAi (dark gray column) lines grown at 22°C (I and K) and after incubation for 3 days at 30°C (J and L). The third-youngest fruits of stage 17 flowers as described by Smyth et al. [19] were examined. Results were obtained from two independent T2 lines for RNAi-control and CLE45-RNAi. Each data point represents the mean of 12 fruits from a compilation of three experiments ± SD. Asterisks indicate significant differences (p < 0.05 by two-sample t test) between CLE45-RNAi lines and the other WT and RNAi-control lines. Representative fruits after incubation for 3 days at 30°C are shown in (M).See also Figure S1.
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Figure 2. Identification and Characterization of Putative Receptors for CLE45 Peptide(A–D) Effects of synthetic CLE45 or CLE43 peptide on the growth of skm pollen tubes in vitro. Pollen grains of WT (A), skm1 and the complemented mutant skm1 harboring pSKM1::SKM1-YFP (skm1 SKM1) (B), skm2 and the complemented mutant skm2 harboringpSKM2::SKM2-YFP (skm2 SKM2) (C), and the skm1 skm2 double mutant (D) were cultured in the presence (solid lines with filled circles) or absence (dashed lines with filled squares) of synthetic CLE45 or CLE43 peptide for 20 hr at 30°C, and the number of pollen tubes with indicated length was measured. Each data set represents the mean of four independent cultures ± SD. Pollen mixtures of three independent T1 lines were used for skm1 SKM1 and skm2 SKM2; 30–40 pollen tubes were measured in each culture.(E and F) SKM2 expression by GUS reporter in pSKM2::GUStransgenic Arabidopsis flowers. Pollen grains of 7-week-old plants without (E) or with (F) incubation for 24 hr at 30°C are shown. Scale bars represent 100 μm.(G and H) SKM1 expression by YFP reporter in a pSKM1::SKM1-YFP transgenicskm1 mutant. Isolated pollen grains from 7-week-old plants without (G) or with (H) incubation for 24 hr at 30°C are shown. Scale bars represent 100 μm.(I–L) Functional analysis of SKM1 and SKM2 in Arabidopsis plants. Numbers of developing seeds (I and J) and fruit lengths (K and L) were measured in WT, skm1, skm1 skm2 double mutant, andskm1 harboring either pSKM1::SKM1-YFP (skm1 SKM1; light gray column) or the kinase-dead version (skm1 KDSKM1; dark gray column) grown at 22°C (I and K) and after incubation for 3 days at 30°C (J and L). The third-youngest fruits of the stage 17 flowers as described by Smyth et al. [19] were examined. Results were obtained from two independent T2 lines for skm1 SKM1 and skm1 KDSKM1. Each data point represents the mean of at least ten fruits for seed number and six for fruit length from a compilation of three experiments ± SD. Asterisks indicate significant differences (p < 0.05 by two-sample t test) between skm1 KDSKM1 lines and the other plants, including WT, skm1, skm1 skm2 double mutant, and skm1 SKM1 lines.See also Figure S2 and Table S1.
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Figure 3. Interaction between Pistil CLE45 and Pollen SKM1(A–C) Seed production in pistils artificially pollinated under high-temperature conditions. Numbers of developing seeds were measured in the indicated crosses. Plants were incubated for 18 hr at 30°C (A and B) or 33°C (C) after artificial pollination and then grown further for 3 days at 22°C. Results were obtained from each of the T2 lines used in Figures 1 and 2 for CLE45-RNAi, skm1 SKM1, and skm1KDSKM1. Each data point represents the mean of five to eight crossed pistils ± SD. Asterisks indicate significant differences (∗p < 0.05, ∗∗p < 0.10 by two-sample t test) between RNAi-control and CLE45-RNAi or between skm1 SKM1 and skm1 KDSKM1 in (A), and between the WT and the other crosses in (C).(D–F) In vitro CLE45 peptide-SKM1 protein binding assay.(D) Pollen grains of WT Arabidopsis were cultured for 20 hr at 30°C in the presence (solid lines with filled circles) or absence (dashed lines with filled squares) of ASA-CLE45 peptide. Each data set represents the mean of four independent cultures ± SD; 30–40 pollen tubes were measured in each culture.(E) The SKM1-HaloTag form protein (At2g25790) visualized by HaloTag TMR reagent.(F) Photoaffinity labeling of SKM1-HT by [125I]ASA-CLE45 in the absence or presence of excess unlabeled CLE45, CLE2, or RGF1 peptides. The photoaffinity labeling experiment was repeated and gave the same result.
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Figure 4. Characterization of CLE45 Peptide Activity in Alleviating Mitochondrial Decay during Arabidopsis Pollen Tube Culture In Vitro(A) Time-lapse observation of WT Arabidopsis pollen tube growth with or without synthetic CLE45 peptide. Lengths of five pollen tubes at the indicated culture periods were measured in the presence (solid lines with filled circles, lower panel) or absence (dashed lines with filled squares, upper panel) of synthetic CLE45 peptide.(B) Effect of synthetic CLE45 peptide in a culture condition at 22°C on WT Arabidopsis pollen tube growth. Pollen grains of WT Arabidopsis were cultured for 20 hr at 22°C in the presence (solid lines with filled circles) or absence (dashed lines with filled squares) of synthetic CLE45 peptide. Each data set represents the mean of four independent cultures ± SD; 30–40 pollen tubes were measured in each culture.(C–G) Effect of synthetic CLE45 peptide on Arabidopsis pollen tube viability by MTT staining.(C–E) MTT-negative (C) and -positive (D) pollen tubes at 4 hr of culture. The boxed area in (D) is magnified in (E).(F) Proportion of MTT-positive pollen tubes at the indicated time points of in vitro culture with synthetic CLE45 (black solid lines with filled triangles), CLE43 (gray solid lines with open triangles), CLV3 (gray dashed lines with open squares), or no peptide (black dashed lines with filled squares). The y axis uses a logarithmic scale. Each data point represents the mean of four independent cultures ± SD; 200 pollen tubes were measured in each culture.(G) Proportion of MTT-positive pollen tubes from WT, skm1 skm2 double mutant, and its partially complemented lines. Pollen tubes were cultured for 20 hr at 30°C. Each data point represents the mean of at least four independent cultures ± SD; 100–200 pollen tubes were observed in each culture. Pollen mixtures of three independent T2 lines were used for the skm1 skm2 double mutant harboring either pSKM1::SKM1-YFP (skm1 skm2 SKM1) or pSKM2::SKM2-YFP (skm1 skm2 SKM2). Asterisks indicate significant differences (p < 0.05 by two-sample t test) between the presence (+) and absence (–) of synthetic CLE45 peptide.
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Copyright © 2013 Elsevier Ltd. All rights reserved.

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