Abstract
Small Auxin Up RNA genes (SAURs) are early auxin-responsive genes, but whether any of them are involved in leaf senescence is not known. Auxin, on the other hand, has been shown to have a role in leaf senescence. Some of the external application experiments indicated that auxin can inhibit leaf senescence, whereas other experiments indicated that auxin can promote leaf senescence. Here, we report the identification and characterization of an Arabidopsis (Arabidopsis thaliana) leaf senescence-associated gene named SAG201, which is highly up-regulated during leaf senescence and can be induced by 1-naphthaleneacetic acid, a synthetic auxin. It encodes a functionally uncharacterized SAUR that has been annotated as SAUR36. Leaf senescence in transfer DNA insertion saur36 knockout lines was delayed as revealed by analyses of chlorophyll content, F(v)/F(m) ratio (a parameter for photosystem II activity), ion leakage, and the expression of leaf senescence marker genes. In contrast, transgenic Arabidopsis plants overexpressing SAUR36 (without its 3' untranslated region [UTR]) displayed an early leaf senescence phenotype. However, plants overexpressing SAUR36 with its 3' UTR were normal and did not exhibit the early-senescence phenotype. These data suggest that SAUR36 is a positive regulator of leaf senescence and may mediate auxin-induced leaf senescence and that the 3' UTR containing a highly conserved downstream destabilizes the SAUR36 transcripts in young leaves.
Highlights
Small Auxin Up RNA genes (SAURs) are early auxin-responsive genes, but whether any of them are involved in leaf senescence is not known
The Expression of SAG201/SAUR36 Is Up-Regulated during Leaf Senescence in Arabidopsis
Quantitative PCR analyses revealed that the transcript levels of SAG201/SAUR36 were very low in expanding young leaves and fully expanded mature leaves but increased with the progression of senescence (Fig. 1, A and B)
Summary
Small Auxin Up RNA genes (SAURs) are early auxin-responsive genes, but whether any of them are involved in leaf senescence is not known. Plants overexpressing SAUR36 with its 39 UTR were normal and did not exhibit the early-senescence phenotype These data suggest that SAUR36 is a positive regulator of leaf senescence and may mediate auxin-induced leaf senescence and that the 39 UTR containing a highly conserved downstream destabilizes the SAUR36 transcripts in young leaves. Thousands of SAGs have been isolated, including genes encoding transcription factors, signal transduction components, proteinases and other catabolic enzymes, and various transporters of sugars, amino acids, and other nutrients (Gepstein et al, 2003; Guo et al, 2004; Buchanan-Wollaston et al, 2005; Guo and Gan, 2012). Some correlative studies showed that the total auxin levels decrease as leaf senescence progresses (Gan, 2010) These findings suggest that auxin may be a negative regulator of leaf senescence. The function and underlying mechanisms of many SAUR genes remain unknown
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