Plant-specific GRAS transcription factors play important roles in regulating growth, development, and stress responses. Castor beans (Ricinus communis) are important non-edible oilseed plants, cultivated worldwide for its seed oils and its adaptability to growth conditions. In this study, we identified and characterized a total of 48 GRAS genes based on the castor bean genome. Combined with phylogenetic analysis, the castor bean GRAS members were divided into 13 distinct groups. Functional divergence analysis revealed the presence of mostly Type-I functional divergence. The gene structures and conserved motifs, both within and outside the GRAS domain, were characterized. Gene expression analysis, performed in various tissues and under a range of abiotic stress conditions, uncovered the potential functions of GRAS members in regulating plant growth development and stress responses. The results obtained from this study provide valuable information toward understanding the potential molecular mechanisms of GRAS proteins in castor beans. These findings also serve as a resource for identifying the genes that allow castor beans to grow in stressful conditions and to enable further breeding and genetic improvements in agriculture.

Stress-associated proteins (SAPs) are known as response factors to multiple abiotic and biotic stresses in plants. However, the potential physiological and molecular functions of SAPs remain largely unclear. Castor bean (Ricinus communis L.) is one of the most economically valuable non-edible woody oilseed crops, able to be widely cultivated in marginal lands worldwide because of its broad adaptive capacity to soil and climate conditions. Whether SAPs in castor bean plays a key role in adapting diverse soil conditions and stresses remains unknown. In this study, we used the castor bean genome to identify and characterize nine castor bean SAP genes (RcSAP). Structural analysis showed that castor bean SAP gene structures and functional domain types vary greatly, differing in intron number, protein sequence, and functional domain type. Notably, the AN1-C2H2–C2H2 zinc finger domain within RcSAP9 has not been often observed in other plant families. High throughput RNA-seq data showed that castor bean SAP gene profiles varied among different tissues. In addition, castor bean SAP gene expression varied in response to different stresses, including salt, drought, heat, cold and ABA and MeJA, suggesting that the transcriptional regulation of castor bean SAP genes might operate independently of each other, and at least partially independent from ABA and MeJA signal pathways. Cis-element analyses for each castor bean SAP gene showed that no common cis-elements are shared across the nine castor bean SAP genes. Castor bean SAPs were localized to different regions of cells, including the cytoplasm, nucleus, and cytomembrane. This study provides a comprehensive profile of castor bean SAP genes that advances our understanding of their potential physiological and molecular functions in regulating growth and development and their responses to different abiotic stresses.

Cellular autophagy is a widely-occurring conserved process for turning over damaged organelles or recycling cytoplasmic contents in cells. Although autophagy-related genes (ATGs) have been broadly identified from many plants, little is known about the potential function of autophagy in mediating plant growth and development, particularly in recycling cytoplasmic contents during seed development and germination. Castor bean (Ricinus communis) is one of the most important inedible oilseed crops. Its mature seed has a persistent and large endosperm with a hard and lignified seed coat, and is considered a model system for studying seed biology. Here, a total of 34 RcATG genes were identified in the castor bean genome and their sequence structures were characterized. The expressional profiles of these RcATGs were examined using RNA-seq and real-time PCR in a variety of tissues. In particular, we found that most RcATGs were significantly up-regulated in the later stage of seed coat development, tightly associated with the lignification of cell wall tissues. During seed germination, the expression patterns of most RcATGs were associated with the decomposition of storage oils. Furthermore, we observed by electron microscopy that the lipid droplets were directly swallowed by the vacuoles, suggesting that autophagy directly participates in mediating the decomposition of lipid droplets via the microlipophagy pathway in germinating castor bean seeds. This study provides novel insights into understanding the potential function of autophagy in mediating seed development and germination.

Phosphoglucose isomerase (PGI), which catalyzes the interconversion of glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P), plays a key role in regulating carbohydrate synthesis and catabolism in plant growth and development. In higher plants, two PGI isoenzymes, plastidic (PGIp) and cytosolic (PGIc), have diverged significantly in sequence, structure, activity, and functional roles, despite catalyzing the same reaction. However, whether they experience distinct selection pressures during intraspecific population differentiation remains unknown. In this study, we identified the PGIc and PGIp genes in castor beans, an important industrial and horticultural crop, and revealed their different expression patterns across tissues, particularly during seed development. Population genetic analyses (Tajima’s D, ML-HKA, and CODEML) detected strong evidence of positive selection on RcPGIc, but not RcPGIp during domestication. Four positively selected sites in RcPGIc (114T, 310T, 338A, and 613S) were inferred with posterior probabilities > 95% in BEB analysis, and two of them (114T and 613S) were found to be significantly associated with higher seed oil content, suggesting that these two sites could potentially influence oil accumulation in castor seeds. This study provides the first evidence of differential selection pressures on PGIc and PGIp during intraspecific population differentiation, offering new insights into their functional divergence.

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B-cell lymphoma 2 ( Bcl-2 ) has a dual function, acting both as an oncogene and an anti-tumor gene. It is well known that Bcl-2 exerts its tumor promoting function through the mitochondrial pathway. However, the mechanism by which Bcl-2 suppresses tumor formation is not well understood. We have previously shown that Bcl-2 inhibits cell cycle progression from the G ₀ /G ₁ to the S phase after serum starvation, and that quiescent Bcl-2 expressing cells maintained a significant lower level of mitochondrial reactive oxygen species (ROS) than the control cells. Based on the fact that ROS mediate cell cycle progression, and are controlled by peroxisome proliferator-activated receptor-γ co-activator 1α (PGC-1α), a key molecule induced by prolonged starvation and involved in mitochondrial metabolism, we hypothesized that PGC-1α might be related with the cell cycle function of Bcl-2. Here, we showed that PGC-1α was upregulated upon Bcl-2 overexpression and downregulated following Bcl-2 knockdown during serum starvation. Knockdown of PGC-1α activated Bcl-2 expression. Taken together, our results suggest that after serum depletion, PGC-la might coordinate with Bcl-2 to reduce ROS, which in turn delay cell cycle progression. Summary statement: PGC-1α coordinate with Bcl-2 delay cell cycle progression to reduce ROS after serum depletion in human glioma U251 cells.