Shaokun Sun

Gamma-aminobutyric acid (GABA), a ubiquitous non-protein amino acid, plays a vital role in the response of plants to biotic and abiotic stresses. This review summarizes the underlying mechanisms through which GABA contributes to plant stress resistance, including its biosynthetic and metabolic pathways, as well as its regulatory roles in enhancing stress tolerance and improving fruit quality. In plants, GABA is primarily synthesized from glutamate by the enzyme glutamate decarboxylase (GAD) and further metabolized by GABA transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH). The accumulation of GABA regulates various physiological and biochemical processes, including the control of stomatal closure, enhancement of antioxidant capacity, maintenance of ionic homeostasis, and stabilization of cellular pH. Moreover, GABA interacts with phytohormones to regulate plant growth, development, and stress tolerance. Notably, increasing GAD expression through genetic engineering has been shown to enhance tolerance to stresses, such as drought, saline-alkali, cold, and heat, in various plants, including tomato, rice, and creeping bentgrass. Additionally, GABA has effectively improved the storage quality of various fruits, including citrus fruits, apples, and strawberries. In conclusion, GABA holds significant research potential and promising applications in agricultural production and plant science.

Ethylene (ET) influences the synthesis of anthocyanins, although its regulatory effects can differ significantly across various plant species. In apples (Malus domestica), ET promotes anthocyanin synthesis, whereas in Arabidopsis thaliana, it inhibits its accumulation. Our research showed that ethephon (Eth), an ET derivative, promotes anthocyanin synthesis in ‘Viviana’ lilies, which has great potential in the cut flower industry. The regulatory mechanism whereby ET influences anthocyanin synthesis in lilies remains unclear. In this study, we screened and characterized an ET-induced ET response factors (ERFs), LvERF113, with inhibitory function. Our analyses suggested that LvERF113 could inhibit the negative regulatory function of LvMYB1 at transcriptional and posttranslational levels, promoting anthocyanin synthesis in ‘Viviana’ lily tepals. In addition, LvERF113 is positively regulated by LvMYB5, forming the LvMYB5-LvERF113-LvMYB1 module controlling anthocyanin synthesis by ET in ‘Viviana’ lily. These findings offer new insights into the ET regulatory network of anthocyanin synthesis and provide a theoretical basis for the application of ET derivatives in the cut flower industry.

Anthocyanins, constituents of flavonoid compounds prevalent in plants, possess significant value in both plant development and human nutrition. The regulation of anthocyanin biosynthesis primarily involves the orchestration of MYB, bHLH, and WD40 transcription factors. Consequently, the bHLH family assumes a pivotal role in modulating plant developmental processes. In the present investigation, a transcription factor, denoted as LvbHLH13, was identified as a positive regulator of anthocyanin pigmentation in lily petals. LvbHLH13 is classified within the IIId subgroup of Arabidopsis bHLH proteins. Functional analyses involving the transient expression and gene silencing of LvbHLH13 revealed its capacity to enhance and diminish anthocyanin accumulation, respectively, by modulating the LvMYB5 expression, thereby influencing the downstream structural gene expression. The overexpression of LvbHLH13 resulted in an increase in the expression of the downstream structural genes related to anthocyanin synthesis, whereas silencing of LvbHLH13 correspondingly decreased the expression. Yeast one-hybrid and EMSA assays demonstrated the interaction between LvbHLH13 and the LvMYB5 promoter, leading to the activation of anthocyanin biosynthesis. A further luciferase (LUC) analysis corroborated the stimulatory effect of LvbHLH13 on the LvMYB5 promoter sequence. Consequently, LvbHLH13 assumed a crucial role in lily-petal pigmentation. A yeast two-hybrid analysis revealed that LvbHLH13 diverged from typical bHLH transcription factor behavior as it did not form a complex with MYB to regulate anthocyanin biosynthesis. This discrepancy could be attributed to the deletion of the N-terminal conserved sequence of LvbHLH13. This study provides a new bHLH candidate and bHLH-MYB partner to explore the anthocyanin regulatory network in further research and provides new opportunities for breeding lilies with various anthocyanin contents. These findings lay a theoretical foundation for subsequent investigations into lily flower coloring mechanisms.

Lily (Lilium spp.), a horticultural crop serving both ornamental and edible functions, derives its coloration primarily from anthocyanins. However, limited studies have been conducted on the accumulation of anthocyanins within lilies. In this study, we cloned a light-induced transcription factor named as LvBBX24 in lilies. Through genetic and biochemical analysis, we determined that LvBBX24 could upregulate the transcription of LvMYB5 and facilitate anthocyanin synthesis. Moreover, we identified that darkness promoted the degradation of LvBBX24 protein. Through screening a yeast library, we identified LvbZIP44 acts as its interacting partner. Genetic testing confirmed that LvbZIP44 also plays a role in promoting lily anthocyanin synthesis. This indicates a potential synergistic regulatory effect between LvBBX24 and LvbZIP44. Our study indicates that LvBBX24 and LvbZIP44 cooperate to regulate anthocyanin accumulation in lily petals. These findings provide compelling evidence supporting the idea that LvBBX24 and LvbZIP44 may form a looped helix surrounding the LvMYB5 promoter region to regulate anthocyanin biosynthesis.