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United States Department of Agriculture

Agricultural Research Service

Title: Putative Protease Inhibitor Gene Discovery and Transcript Profiling During Fruit Development and Leaf Damage in Grapefruit (Citrus Paradisi MAEF.)

Authors
item Shatters, Robert
item Bausher, Michael
item Hunter, Wayne
item Chaparro, Jose
item Dang, Phat
item Niedz, Randall
item Mayer, Richard
item McCollum, Thomas
item Sinisterra, Xiomara - UNIV. OF FLORIDA

Submitted to: Gene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 13, 2003
Publication Date: February 4, 2004
Citation: Shatters, R.G., Bausher, M.G., Hunter, W.B., Chaparro, J.X., Dang, P.M., Niedz, R.P., Mayer, R.T., Mccollum, T.G., Sinisterra, X. 2004. Putataive protease inhibitor gene discovery and transcript profiling during fruit development and leaf damage in grapefruit (citrus paradisi macf). Gene 326:77-86

Interpretive Summary: As world agriculture turns toward more sustainable and environmentally friendly agricultural practices, new biologically based mechanisms for reducing pest insect damage to our crops are needed. Research is showing that plants have very intricate defensive mechanisms to reduce susceptibility to attack by insects and diseases. Understanding how these mechanisms work, and how some pests and diseases avoid them, is key to developing new environmentally friendly agricultural practices. Work in this paper was performed by U. S. Horticultural Research Laboratory researchers to discover new proteins (protease inhibitors, PI) produced by citrus that function as defensive molecules protecting the plant against pest insect attack by inhibiting insect digestion. Seven new citrus PI were discovered using a citrus functional genomics strategy. Activity of the genes encoding these PI was highest in young plant tissues, but these tissues, that are also sensitive to insect feeding attack, were unable to elevate the activate of these genes as a result of Diaprepes root weevil (DRW) feeding damage. However, mature leaves that are resistant to insect feeding did activate one of the PI genes in response to DRW feeding damage. Understanding how these PI genes function in plant protection and how economically important agricultural insect pests avoid the activity of plant PIs will provide the information needed to improve natural plant defensive strategies. This can be realized either through direct application of plant defensive compounds or elicitors, or through selective breeding techniques to improve the expression and function of natural plant defensive components.

Technical Abstract: Seven putative protease inhibitor (PPI) cDNAs, representing four protein families, were isolated from a grapefruit (Citrus paradisi Maef. Cv. Marsh) immature fruit flavedo cDNA library. Clones represented: legume Kuntiz inhibitors (LkiL-1, LkiL-2, LkiL-3), potato trypsin inhibitor I (PtiIL-1), serpins (SerpL-1), cystatins (CysL-1), and gamma thionins (GthL-1). Response of transcript abundance to fruit development and leaf wounding was determined for all but LkiL-3 using real-time RT-PCR. Immature leaves had the highest transcript levels for all PPIs. The GthL-1 transcript in immature leaves was the most abundant transcript but was absent from healthy mature leaves. Transcripts for all PPIs were most abundant in flavedo of youngest fruit (<15mm dia. fruit), and declined during development. Mechanical or Diaprepes root weevil feeding damage to leaves caused a <10-fold reduction or had no effect on transcript level with the exception of GthL-1 which as a result of damage increased >50-fold in mature leaves and decreased >1400-fold in immature leaves. Except for GthL-1, the PPI transcripts were more responsive to development than to wounding. Changes in PPI transcript levels suggest diverse roles for the products of these genes in citrus, with only GthL-1 responding in a defense-like manner.

Last Modified: 12/21/2014
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