Abstract
Copper (Cu) is an essential element for most living plants, but it is toxic for plants when present in excess. To better understand the response mechanism under excess Cu in plants, especially in flowers, transcriptome sequencing on petunia buds and opened flowers under excess Cu was performed. Interestingly, the transcript level of FIT-independent Fe deficiency response genes was significantly affected in Cu stressed petals, probably regulated by basic-helix-loop-helix 121 (bHLH121), while no difference was found in Fe content. Notably, the expression level of bHLH121 was significantly down-regulated in petals under excess Cu. In addition, the expression level of genes related to photosystem II (PSII), photosystem I (PSI), cytochrome b6/f complex, the light-harvesting chlorophyll II complex and electron carriers showed disordered expression profiles in petals under excess Cu, thus photosynthesis parameters, including the maximum PSII efficiency (FV/FM), nonphotochemical quenching (NPQ), quantum yield of the PSII (ΦPS(II)) and photochemical quenching coefficient (qP), were reduced in Cu stressed petals. Moreover, the chlorophyll a content was significantly reduced, while the chlorophyll b content was not affected, probably caused by the increased expression of chlorophyllide a oxygenase (CAO). Together, we provide new insight into excess Cu response and the Cu–Fe crosstalk in flowers.
Highlights
Copper (Cu) is an essential micronutrient for most living plants as a cofactor in metalloproteins involved in many biological processes, such as ethylene signaling, reactive oxygen species (ROS) response, photosynthesis and respiration [1]
The Cu deficiency response in Arabidopsis roots is controlled by squamosa promoter binding protein-Like7 (SPL7), which is constitutively expressed in roots [11]
We investigated the transcriptional response to excess Cu in petunia petals, and provided new insights into the crosstalk between iron and copper homeostasis
Summary
Copper (Cu) is an essential micronutrient for most living plants as a cofactor in metalloproteins involved in many biological processes, such as ethylene signaling, reactive oxygen species (ROS) response, photosynthesis and respiration [1]. Several proteins have been reported involved in Cu detoxification, such as metallothioneins (MTs), heavy metal P-type ATPases (HMA5I and HMA5II) and Copper chaperons (CCH) [8,9,10]. The Cu deficiency response in Arabidopsis roots is controlled by squamosa promoter binding protein-Like (SPL7), which is constitutively expressed in roots [11]. Under Cu deficiency, SPL7 activates expression of copper transporter (COPT2), ferric reductase oxidase 4 (FRO4) and FRO5 which promotes Cu uptake into the roots [11,12]
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