Specific role of LeMAN2 in the control of seed germination exposed by overexpression of the LeMAN3 gene in tomato plants

Harel Belotserkovsky, Yael Berger, Ron Shahar, Shmuel Wolf*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Endo-β-mannanase is one of the key enzymes involved in the hydrolysis of the mannan-rich cell walls of tomato (Solanum lycopersicon) seeds. Two isoforms of endo-β-mannanase have been characterized in tomato seeds: LeMAN2 is active in the micropylar area prior to germination and LeMAN1 is active after germination in all endosperm cells surrounding the cotyledons. To explore whether general mannanase activity in the endosperm cap is sufficient to promote germination, the gene encoding LeMAN3 was inserted into transgenic tomato plants under the control of a CaMV-35S promoter. Expression of LeMAN3 was evident in the endosperm cap and in the lateral endosperm of the transgenic seeds 10 min after imbibition. An activity test indicated increased activity of endo-β-mannanase in the transgenic lines relative to the control line in all seed parts, during the first 20 h of imbibition. However, overexpression of LeMAN3 in transgenic seeds inhibited seed germination at both optimal and suboptimal temperatures. Detailed RT-PCR analyses revealed the transcription patterns of the genes encoding the various mannanase isoforms, and indicated a delay in LeMAN2 transcription in the endosperm cap of the transgenic seeds. Interestingly, tissue-print assays indicated similar mannanase activity in the micropylar areas for both transgenic and control seeds. These results indicate that overexpression of active endo-β-mannanase in the endosperm cap is not sufficient to enable hydrolysis of the cell walls or to promote germination of tomato seeds. Cell-wall hydrolysis in these endosperm cells is under tight control and requires the specific activity of LeMAN2.

Original languageAmerican English
Pages (from-to)199-209
Number of pages11
JournalPlanta
Volume227
Issue number1
DOIs
StatePublished - Dec 2007

Bibliographical note

Funding Information:
Acknowledgments The authors thank Amnon Sharir (The Hebrew University) for his assistance in the puncture force determination experiments. Profs. Jaime Kigel (The Hebrew University) and Gad Ga-lili (The Weizmann Institute of Science) are gratefully acknowledged for the critical reviewing of the manuscript. This paper is a contribution from the Uri Kinamon Laboratory. H.B. and Y.B were supported by a scholarship from the Kinamon Foundation. Support of this project by the German Federal Ministry of Education and Research (BMBF) within the framework of the German-Israeli Project Cooperation (DIP) is gratefully acknowledged.

Keywords

  • Cell wall
  • Endo-β-mannanase
  • Endosperm
  • Solanum

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