Calcium serves as a second messenger in various signal transduction pathways in plants. CBL-interacting protein kinases (CIP-Ks), which have a variety of functions, are involved in calcium signal transduction. Previous, the studies on CIPK family members focused on Arabidopsis and rice. Here, we present a comparative genomic analysis of the CIPK gene family in Arabidopsis and poplar, a model tree species. Twenty-seven potential CIPKs were identified from poplar using genome-wide analysis. Like the CIPK gene family from Arabidopsis, CIPK genes from poplar were also divided into intron-free and intronharboring groups. In the intron-harboring group, the intron distribution of CIPKs is rather conserved during the genome evolutionary process. Many homologous gene pairs were found in the CIPK gene family, indicating duplication events might contribute to the amplification of this gene family. The phylogenetic comparison of CIPKs in combination with intron distribution analysis revealed that CIPK genes from both Arabidopsis and poplar might have an ancient origin, which formed earlier than the separation of these two eudicot species. Our genomic and bioinformatic analysis will provide an important foundation for further functional dissection of the CBL-CIPK signaling network in poplars.

Calcium plays a critical role in regulating abiotic-stress response in plant. Calcineurin B-like (CBL) proteins have been identified as calcium sensors in the calcium signaling pathway in Arabidopsis and rice. However, molecular mechanism underlying calcium signaling remains to be elucidated, especially in poplar, a model tree species with complete sequencing of the whole genome. Here, we have characterized 10 CBL candidate genes in the genome of Populus trichocarpa (PtCBLs) and presented a comparative genomics analysis of CBLs in poplar, rice and Arabidopsis, including gene structures, conserved motifs and phylogeny. Comparative genomics analyses showed that the family in poplar appears to be rather conserved in the size and structure, and the duplication events might significantly contribute to the amplification of this gene family. Furthermore, to elucidate the functions of CBL gene members respectively in regulating plant response to external stimuli, we presented a study of CBL family in Populus euphratica (PeCBLs), a mostly salt-and drought-tolerant Populus species. Nine cDNA clones of PeCBL members were isolated from Populus euphratica and a gene specific RT-PCR was performed to investigate their expression patterns under abiotic stress treatment, such as cold, drought, and salt. A transcript analysis of CBLs in Populus euphratica under abiotic stress suggests that seven CBL gene (PeCBL1, 2, 3, 4, 5, 9, and 10) members may play an important role in correspondence to specific external stimuli. Our data will provide important evidence for further studying the functional dissection of the CBL signaling network in plant.

This paper is the first to directly link two types of ion channel regulation pathway into an emerging and complex CBL-CIPK signal system in wooden plant. In Arabidopsis thaliana, the calcineurin b-like (CBL) 1 gene has been shown to be necessary in response to abiotic stresses. In this study, we identified CBL1 in the woody plant Populus euphratica, designated as PeCBL1. Heterologous expression of PeCBL1 could build the resistance of sensitive phenotypes to low K(+) stress in the corresponding Arabidopsis cbl1/cbl9 mutant, and display a salt-sensitive phenotype compared with the mutant. Protein interaction analysis showed that PeCBL1 can interact with PeCIPK24, 25 and 26, and form different complexes of PeCBL-PeCIPK. To further investigate the mechanism of PeCBL1, we analyzed the fluxes of K(+) and Na(+) in roots of the wild-type Arabidopsis, cbl1/9 mutant, and PeCBL1 transgenic plants under low K(+) stress and high Na(+) stress. These analyses revealed that, compared to the cbl1/9 mutant, the PeCBL1 transgenic plant roots exhibited a higher capacity to absorb K(+) after exposure to low K(+) stress, and a lower capacity to discharge Na(+) after exposure to salt stress. The results suggest that CBL1 interacts with CIPK24, CIPK25 and CIPK26 to regulate Na(+)/K(+) homeostasis in Populus euphratica.

Flavonoids are secondary metabolites widely distributed among angiosperms, where they play diverse roles in plant growth, development, and evolution. The regulation of flavonoid biosynthesis in plants has been extensively studied at the transcriptional level, but post-transcriptional, translational, and post-translational control of flavonoid biosynthesis remain poorly understood. In this study, we analysed post-translational regulation of flavonoid biosynthesis in the ornamental plant Paeonia, using proteome and ubiquitylome profiling, in conjunction with transcriptome data. Three enzymes involved in flavonoid biosynthesis were identified as being putative targets of ubiquitin-mediated degradation. Among these, chalcone synthase (PhCHS) was shown to have the greatest number of ubiquitination sites. We examined PhCHS abundance in petals using PhCHS-specific antibody and found that its accumulation decreased at later developmental stages, resulting from 26S proteasome-mediated degradation. We further identified a ring domain-containing protein (PhRING-H2) that physically interacts with PhCHS and demonstrated that PhRING-H2 is required for PhCHS ubiquitination. Taken together, our results suggest that PhRING-H2-mediates PhCHS ubiquitination and degradation is an important mechanism of post-translational regulation of flavonoid biosynthesis in Paeonia, providing a theoretical basis for the manipulation of flavonoid biosynthesis in plants.