Calcium‐dependent protein kinases (CDPKs) are sensor‐transducer proteins capable of decoding calcium signals in diverse phosphorylation‐dependent calcium signaling networks in plants and some protists. Using a novel yeast two‐hybrid (YTH) approach with constitutively active and/or catalytically inactive forms of AtCPK11 as bait, we identified AtDi19 as an AtCPK11‐interacting protein. AtDi19 is a member of a small family of stress‐induced genes. The interaction was confirmed using pull‐down assays with in vitro translated AtCPK11 and GST–AtDi19 and localization studies in Arabidopsis protoplasts cotransfected with AtCPK11:GFP and AtDi19:DsRed2 protein fusions. We further showed that the interaction of AtDi19 is specific to both AtCPK4 and AtCPK11, whereas other closely related CPKs from Arabidopsis interacted weakly (e.g., AtCPK12) or did not interact (e.g., AtCPK26, AtCPK5 and AtCPK1) with AtDi19. Deletion analyses showed that a region containing two predicted nuclear localization signals (NLS) and a nuclear export signal (NES) of AtDi19 is essential for interaction with AtCPK11. We further demonstrated that AtDi19 is phosphorylated by AtCPK11 in a Ca²⁺‐dependent manner at Thr105 and Ser107 within the AtDi19 bipartite NLS using in vitro kinase assays. Our data suggest that disruption of the autoinhibitor domain leading to the formation of a constitutively active CDPK may stabilize kinase–substrate interactions without affecting specificity.

To improve several agronomic traits in crisphead lettuce (Lactuca sativaL.) under high-temperature growth conditions, we investigated the correlation among those traits in multiple cultivars and performed genetic mapping of their causal genes. In a field cultivation test of Empire type (serrated leaf) and Salinas type (wavy leaf) cultivars, Empire type cultivars showed increased tipburn susceptibility and late bolting compared with Salinas type cultivars. We attempted genetic mapping of leaf shape and bolting time by ddRAD-seq using the F₂population derived from a cross between ‘VI185’ (Empire type) and ‘ShinanoGreen’ (Salinas type). These analyses suggested that both traits are controlled by a single locus in LG5. Genotyping of 51 commercial lettuce cultivars with a tightly linked marker (LG5_v8_252.743Mbp) at this locus showed an association between its genotype and the serrated leaf phenotype. By further fine mapping and transcriptome analysis, a gene encoding putative CIN-like TCP transcription factor was determined to be a candidate gene at this locus and was designated asLsTCP4. An insertion of retrotransposable element was found in the allele of ‘VI185’, and its transcript level in the leaves was lower than that in ‘ShinanoGreen’. Because shapes of leaf epidermal cells in ‘VI185’ were similar to those in the TCP family mutant ofArabidopsis thaliana, the leaf shape phenotype was likely caused by reduced expression ofLsTCP4. Furthermore, because it is known that the TCP family protein also controls flowering time via interaction with FT inA. thaliana, it was highly possible thatLsTCP4gave pleiotropic effects on both leaf shape and bolting time in lettuce.

Plants can synthesize some antioxidants, including L-ascorbic acid (AsA) and polyphenol, in response to environmental stresses. Antioxidants detoxify reactive oxygen species in plants and also aid in human health. In this study, we demonstrate that a novel hydroponic treatment can increase leafy vegetable nutritional quality without retarding growth. Leaf lettuce ( Lactuca sativa ) was grown hydroponically and subjected to rhizosphere drought stress by lowering the water level in the solution tub before harvesting. Appropriate drought stress using this method could increase AsA, polyphenol, and sugar content by 24%, 50%, and 17%, respectively, and decrease nitrate nitrogen content by 18% without reducing yield. Similar effects of drought stress on AsA content were observed in four other plant species. This hydroponic method has a universal potential to increase leafy vegetable quality without reducing yield in controlled environments such as plant factories.

The strawberry fruit contains abundant polyphenols, such as anthocyanins, flavan-3-ol, and ellagitannin. Polyphenol enrichment improves the quality of strawberries and leads to a better understanding of the polyphenol induction process. We measured the total polyphenol content of strawberry fruits under different growth conditions, developmental stages, and treatment conditions during pre-harvest and post-harvest periods. High fruit polyphenol content was observed in cold treatment, which was selected for further analysis and optimization. A transcriptome analysis of cold-treated fruits suggested that the candidate components of polyphenols may exist in the phenylpropanoid pathway. Coverage with a porous film bag excluded the effects of drought stress and produced polyphenol-rich strawberry fruits without affecting quality or quantity. The degree of stress was assessed using known stress indicators. A rapid accumulation of abscisic acid was followed by an increase in superoxide dismutase and DPPH (2,2-Diphenyl-1-picrylhydrazyl) activity, suggesting that the strawberry fruits responded to cold stress immediately, reaching the climax at around 6 days, a trend consistent with that of polyphenol content. These findings enhance our understanding of the mechanism of post-harvest polyphenol accumulation and the value of strawberries as a functional food.