Senescence is the ultimate stage of leaf development in which nutrients are recycled and reallocated to newly developing organs. Our gene ontology analysis revealed enrichment for indole glucosinolate biosynthesis genes (IG) among Senescence-Upregulated Genes (SURGs), which suggests IGs influence senescence. IG are secondary metabolites present in the Brassicaceae plant family, and which possess protective properties against herbivory and pathogen infections. Previous data show that inhibition of IG biosynthesis at the beginning of the pathway results in premature senescence, however blocking this portion of the pathway can lead to loss of other metabolites. The IG transport double mutant pen1/pen3 exhibited premature leaf senescence implicating the export of IG metabolites may play a protective role.
This study hypothesizes that IGs play a protective role preventing premature leaf senescence, and aims to identify the protective IG metabolites. A genetic analysis was performed to define which IG metabolites delay leaf senescence. Mutant lines include biosynthesis gene families CYP81F and IGMT, transport genes PEN1 and PEN3, and regulatory genes MYB51 and MYC2. The progression of senescence was analyzed in homozygous mutant plants, and compared to Arabidopsis thaliana wild-type (WT) plants. Relative SURG expression and total leaf chlorophyll content show pen1/pen3 as the only mutant exhibiting premature leaf senescence of all the tested lines. It may be possible that redundancy in gene families compensate for single gene mutations, thus preventing premature senescence.
IG metabolite quantification in double mutant pen1/pen3 and single mutants, pen1-1 and pen3-1, and WT-Col was performed by our collaborators at University of Florida. The pen single mutants do not display early senescence phenotype. The results demonstrate no differences in IG metabolite levels in WT-Col, single pen mutants and pen1/pen3 double mutant. Data demonstrated that early senescence phenotype in pen1/pen3 is not caused by variations in IG levels. SID2, isochorismate synthase, has a role in SA biosynthesis in leaves. The pen1/pen3/sid2 triple mutant was constructed to investigate whether the early senescence phenotype was dependent on the plant hormone salicylic acid (SA). Total leaf chlorophyll content and relative SURG expression demonstrate that sid2 mutation reversed the early senescence observed in pen1/pen3. pen1/pen3/sid2 triple mutant shows that the premature senescence, exhibited in the transport double mutant, is recovered by the loss of SA. This demonstrates that early senescence displayed in pen1/pen3 double mutant is SA-dependent.
|Commitee:||Fisher, Amanda, Fraser, Deborah|
|School:||California State University, Long Beach|
|School Location:||United States -- California|
|Source:||MAI 82/6(E), Masters Abstracts International|
|Subjects:||Genetics, Biology, Bioengineering, Plant sciences, Bioinformatics|
|Keywords:||Arabidopsis thaliana, Indole glucosinolate, Leaf senescence, Pen1/pen3, Secondary metabolites, sid2, Florida, Biosynthesis, Salicylic acid, Plant hormone, Metabolite levels, Leaf chlorophyll|
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