Abstract
The signal that initiates the age-regulated senescence program in flowers is still unknown. Here we propose for the ephemeral Arabidopsis thaliana flower that it dies because of continued expression of the MADS-box transcription factor AGAMOUS (AG). AG is necessary for specifying the reproductive structures of the flower. Flowers of ag-1, which lack AG, exhibited delayed sepal senescence and abscission. The flowers also had reduced jasmonic acid (JA) content. Other anther-defective sterile mutants deficient in JA, defective in anther dehiscence 1 (dad1) and delayed dehiscence 2 (dde2), exhibited delayed sepal senescence and abscission as well. Manually pollinated dad1 flowers produced siliques but still had delayed senescence, demonstrating that absence of pollination does not cause delayed senescence. When ag-1, dad1 and dde2 flowers were sprayed with 100 μM methyl jasmonate, the sepal senescence and abscission phenotypes were rescued, suggesting that JA has a role in these processes. Our study uncovers a novel role for AG in determining the timing of death of the flower it helps develop and highlights a role for JA in sepal senescence.
Highlights
When AGL42 was constitutively expressed in Arabidopsis, floral senescence was delayed through suppression of components in the ethylene signaling pathway (Chen et al, 2011, 2015)
In addition to its well-described role in specifying stamen organ identity in floral primordia, it is known that AG continues to be expressed in stamens and directly activate the jasmonic acid (JA) biosynthesis gene, DEFECTIVE IN ANTHER DEHISCENCE 1 (DAD1) (Ito et al, 2007)
Researchers have for many years demonstrated through physiological studies that flower senescence is regulated by plant hormones such as ethylene, abscisic acid (ABA) and cytokinins, and by source-sink relationships (Rogers, 2013)
Summary
Some flowers last only a few hours before dying, whereas others may persist for several months before they senesce (Stead, 1992). It is still unknown how senescence is initiated in flowers (van Doorn and Woltering, 2008). In some flowers ethylene is important (Woltering and van Doorn, 1988), with the hormone being produced in the gynoecium following pollination (Hunter et al, 2004; van Doorn and Woltering, 2008). Other flowers senesce independently of pollination and an associated ethylene burst (van Doorn, 1997). For ephemeral flowers (flowers lasting less than a day), no clear effect of pollination on longevity has been found (van Doorn, 1997)
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