An ABA‐regulated and Golgi‐localized protein phosphatase controls water loss during leaf senescence in Arabidopsis

Abstract

SUMMARYIt is known that a senescing leaf loses water faster than a non-senescing leaf and that ABA has an important role in promoting leaf senescence. However, questions such as why water loss is faster, how water loss is regulated, and how ABA functions in leaf senescence are not well understood. Here we report on the identification and functional analysis of a leaf senescence associated gene called SAG113. The RNA blot and GUS reporter analyses all show that SAG113 is expressed in senescing leaves and is induced by ABA in Arabidopsis. The SAG113 expression levels are significantly reduced in aba2 and abi4 mutants. A GFP fusion protein analysis revealed that SAG113 protein is localized in the Golgi apparatus. SAG113 encodes a protein phosphatase that belongs to the PP2C family and is able to functionally complement a yeast PP2C-deficient mutant TM126 (ptc1D). Leaf senescence is delayed in the SAG113 knockout mutant compared with that in the wild type, stomatal movement in the senescing leaves of SAG113 knockouts is more sensitive to ABA than that of the wild type, and the rate of water loss in senescing leaves of SAG113 knockouts is significantly reduced. In contrast, inducible over-expression of SAG113 results in a lower sensitivity of stomatal movement to ABA treatment, more rapid water loss, and precocious leaf senescence. No other aspects of growth and development, including seed germination, were observed. These findings suggest that SAG113, a negative regulator of ABA signal transduction, is specifically involved in the control of water loss during leaf senescence.

ABA signalling is fine-tuned by antagonistic HAB1 variants

“…However, our work provides the first indication of the post-transcriptional regulation of PP2C expression and phosphatase activity in ABA signalling and plant responses to ABA. Previously, it was shown that the nine PP2Cs differ in their subcellular localization 11,29,34 and interactions with PYLs 5,12,13,29 . Our findings suggest that the regulatory mechanisms of PP2Cs are more complex than previously thought, and the post-transcriptional regulation of PP2C expression adds another layer of complexity to ABA signalling and plant adaptation to stress.…”

Towards understanding abscisic acid-mediated leaf senescence

“…Consistently, RPK1 is an upstream component of ABA signaling and its expression is increased in an ABA-dependent manner throughout the progression of leaf senescence. However, induction of RPK1 expression in young plants leads to retarded growth but does not trigger the senescence symptoms, suggesting that function of RPK1 in ABAinduced leaf senescence is dependent on the developmental age.Senescence-associated gene113 (SAG113) is a negative regulator of ABA signaling controlling water loss during senescence in Arabidopsis [5]. SAG113 encodes a Golgi-localized PP2C family protein phosphatase, which is able to complement the yeast PP2C-deficient ptd1 mutant, confirming that SAG113 is the functional ortholog of PTC1.…”

A pivotal role of phosphatidylinositol 3-kinase in delaying of methyl jasmonate-induced leaf senescence

“…1 Our current work has shown that stomatal opening was enhanced with prolonged MeJA treatment and vacuolar lumen was alkalized. The enhanced stomatal aperture was also found in low-acidified vacuolar lumen in MeJA-induced leaf senescence.…”

“…1 As we know, water control is mostly dependent on stomatal movement. Recent report has reported that vacuolar acidification has a key role in ABAinduced stomatal closure.…”