Sessile plants have developed a very delicate system to sense diverse kinds of endogenous developmental cues and exogenous environmental stimuli by using a simple Ca2+ ion. Calmodulin (CaM) is the predominant Ca2+ sensor and plays a crucial role in decoding the Ca2+ signatures into proper cellular responses in various cellular compartments in eukaryotes. A growing body of evidence points to the importance of Ca2+ and CaM in the regulation of the transcriptional process during plant responses to endogenous and exogenous stimuli. Here, we review recent progress in the identification of transcriptional regulators modulated by Ca2+ and CaM and in the assessment of their functional significance during plant signal transduction in response to biotic and abiotic stresses and developmental cues.

Salinity is a major abiotic stressor that limits the growth, development, and reproduction of plants. Our previous metabolic analysis of high salt-adapted callus suspension cell cultures from Arabidopsis roots indicated that physical reinforcement of the cell wall is an important step in adaptation to saline conditions. Compared to normal cells, salt-adapted cells exhibit an increased lignin content and thickened cell wall. In this study, we investigated not only the lignin biosynthesis gene expression patterns in salt-adapted cells, but also the effects of a loss-of-function of CCoAOMT1, which plays a critical role in the lignin biosynthesis pathway, on plant responses to high-salt stress. Quantitative real-time PCR analysis revealed higher mRNA levels of genes involved in lignin biosynthesis, including CCoAOMT1, 4CL1, 4CL2, COMT, PAL1, PAL2, and AtPrx52, in salt-adapted cells relative to normal cells, which suggests activation of the lignin biosynthesis pathway in salt-adapted cells. Moreover, plants harboring the CCoAOMT1 mutants, ccoaomt1-1 and ccoaomt1-2, were phenotypically hypersensitive to salt stress. Our study has provided molecular and genetic evidence indicating the importance of enhanced lignin accumulation in the plant cell wall during the responses to salt stress.

MADS-domain transcription factors play pivotal roles in various developmental processes. The lack of simple loss-of-function phenotypes provides impediments to understand the biological function of some of the MADS-box transcription factors. Here we have characterized the potential role of the Arabidopsis thaliana AGAMOUS-LIKE6 (AGL6) gene by fusing full-length coding sequence with transcriptional activator and repressor domains and suggest a role for AGL6 in lateral organ development and flowering. Upon photoperiodic induction of flowering, AGL6 becomes expressed in abaxial and proximal regions of cauline leaf primordia, as well as the cryptic bracts subtending flowers. In developing flowers, AGL6 is detected in the proximal regions of all floral organs and in developing ovules. Converting AGL6 into a strong activator through fusion to the VP16 domain triggers bract outgrowth, implicating AGL6 in the development of bractless flowers in Arabidopsis. In addition, ectopic reproductive structures form on both bracts and flowers in gAGL6::VP16 transgenic plants, which is dependent on B and C class homeotic genes, but independent of LEAFY. Overexpression of both AGL6 and its transcriptional repressor form, AGL6::EAR, causes precocious flowering and terminal flower formation, suggesting that AGL6 suppresses the function of a floral repressor.

Dongwon Baek, Hyun Jin Chun, Songhwa Kang, Gilok Shin, Su Jung Park, Hyewon Hong, Chanmin Kim, Doh Hoon Kim, Sang Yeol Lee, Min Chul Kim, and Dae-Jin Yun. Mol. Cells 2016;39:111-8. https://doi.org/10.14348/molcells.2016.2188

The GIGANTEA-ENHANCED EM LEVEL complex enhances plant tolerance to drought by modulating the diurnal transcription of a gene encoding a rate-limiting enzyme in

Dongwon Baek, Hyun Jin Chun, Dae-Jin Yun, and Min Chul Kim. Mol. Cells 2017;40:. https://doi.org/10.14348/molcells.2017.0192