Abstract
Cellular calcium acts as a second messenger and regulates diverse developmental events and stress responses. Cytosolic calcium has long been considered as an important regulator of senescence, however, the role of Ca2+ in plant senescence has remained elusive. Here we show that the Calmodulin 1 (CaM1) gene, which encodes Ca2+-binding protein calmodulin 1, positively regulates leaf senescence in Arabidopsis. Yellowing of leaves, accumulation of reactive oxygen species (ROS), and expression of the senescence-associated gene 12 (SAG12) were significantly enhanced in CaM1 overexpression plants. In contrast, abscisic acid (ABA)-triggered ROS production and stomatal closure were reduced in amiRNA-CaM1 plants. We found a positive-feedback regulation loop among three signaling components, CaM1, RPK1, and RbohF, which physically associate with each other. RPK1 positively regulates the expression of the CaM1 gene, and the CaM1 protein, in turn, up-regulates RbohF gene expression. Interestingly, the expression of CaM1 was down-regulated in rbohD, rbohF, and rbohD/F mutants. We show that CaM1 positively regulates ROS production, leaf senescence, and ABA response in Arabidopsis.
Highlights
Leaf senescence is the terminal stage of leaf development and is genetically programmed
To identify calmodulin genes that are involved in plant senescence, in silico analysis using publicly available microarray data was conducted and showed that the expression of Arabidopsis CaM genes can be divided into two groups during leaf senescence: age-dependent increase (CaM1, CaM3, and CaM4) and age-dependent decrease (CaM2, CaM5, and CaM7) (Schmid et al, 2005)
This implies that Calmodulin 1 (CaM1), CaM3, and CaM4 probably play a positive role in Arabidopsis leaf senescence
Summary
Leaf senescence is the terminal stage of leaf development and is genetically programmed. Apparent morphological changes involved in leaf senescence include the yellowing of leaves caused by the degradation of chlorophyll, followed by reduction in photosynthesis and protein synthesis. The metabolism and structure of leaf cells continuously change to effectively utilize plant nutrients for the developing parts of the plant, including young leaves, seeds, and fruits (Lim et al, 2007). Calcium is a universal second messenger that exerts an allosteric effect on many enzymes and proteins in various cellular responses.
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