Network of GRAS transcription factors in plant development, fruit ripening and stress responses

The plant-specific family of GRAS transcription factors has been wide implicated in the regulation of transcriptional reprogramming associated with a diversity of biological functions ranging from plant development processes to stress responses. Functional analyses of GRAS transcription factors supported by in silico structural and comparative analyses are emerging and clarifying the regulatory networks associated with their biological roles. In this review, a detailed analysis of GRAS proteins' structure and biochemical features as revealed by recent discoveries indicated how these characteristics may impact subcellular location, molecular mechanisms, and function. Nomenclature issues associated with GRAS classification into different subfamilies in diverse plant species even in the presence of robust genomic resources are discussed, in particular how it affects assumptions of biological function. Insights into the mechanisms driving evolution of this gene family and how genetic and epigenetic regulation of GRAS contributes to subfunctionalization are provided. Finally, this review debates challenges and future perspectives on the application of this complex but promising gene family for crop improvement to cope with challenges of environmental transition.

Genome-Wide Identification and Analysis of the GRAS Transcription Factor Gene Family in Theobroma cacao

GRAS genes exist widely and play vital roles in various physiological processes in plants. In this study, to identify Theobroma cacao (T. cacao) GRAS genes involved in environmental stress and phytohormones, we conducted a genome-wide analysis of the GRAS gene family in T. cacao. A total of 46 GRAS genes of T. cacao were identified. Chromosomal distribution analysis showed that all the TcGRAS genes were evenly distributed on ten chromosomes. Phylogenetic relationships revealed that GRAS proteins could be divided into twelve subfamilies (HAM: 6, LISCL: 10, LAS: 1, SCL4/7: 1, SCR: 4, DLT: 1, SCL3: 3, DELLA: 4, SHR: 5, PAT1: 6, UN1: 1, UN2: 4). Of the T. cacao GRAS genes, all contained the GRAS domain or GRAS superfamily domain. Subcellular localization analysis predicted that TcGRAS proteins were located in the nucleus, chloroplast, and endomembrane system. Gene duplication analysis showed that there were two pairs of tandem repeats and six pairs of fragment duplications, which may account for the rapid expansion in T. cacao. In addition, we also predicted the physicochemical properties and cis-acting elements. The analysis of GO annotation predicted that the TcGRAS genes were involved in many biological processes. This study highlights the evolution, diversity, and characterization of the GRAS genes in T. cacao and provides the first comprehensive analysis of this gene family in the cacao genome.

Melatonin delays dark-induced leaf senescence by inducing miR171b expression in tomato

Melatonin functions in multiple aspects of plant growth, development, and stress response. Nonetheless, the mechanism of melatonin in plant carbon metabolism remains largely unknown. In this study, we investigated the influence of melatonin on the degradation of starch in tomato leaves. Results showed that exogenous melatonin attenuated carbon starvation-induced chlorophyll degradation and leaf senescence. In addition, melatonin delayed leaf starch degradation and inhibited the transcription of starch-degrading enzymes after sunset. Interestingly, melatonin-alleviated symptoms of leaf senescence and starch degradation were compromised when the first key gene for starch degradation, α-glucan water dikinase (GWD), was overexpressed. Furthermore, exogenous melatonin significantly upregulated the transcript levels of several microRNAs, including miR171b. Crucially, the GWD gene was identified as a target of miR171b, and the overexpression of miR171b ameliorated the carbon starvation-induced degradation of chlorophyll and starch, and inhibited the expression of the GWD gene. Taken together, these results demonstrate that melatonin promotes plant tolerance against carbon starvation by upregulating the expression of miR171b, which can directly inhibit GWD expression in tomato leaves.