As sessile organisms, plants face a variety of environmental challenges. Their reproduction and survival depend on their ability to adapt to these stressors, which include water, heat stress, high salinity, and pathogen infection. Failure to adapt to these stressors results in programmed cell death and decreased viability, as well as reduced productivity in the case of crop plants. The growth and development of plants are maintained by meiosis and mitosis as well as endoreduplication, during which DNA replicates without cytokinesis, leading to polyploidy. As in other eukaryotes, the cell cycle in plants consists of four stages (G1, S, G2, and M) with two major check points, namely, the G1/S check point and G2/M check point, that ensure normal cell division. Progression through these checkpoints involves the activity of cyclin-dependent kinases and their regulatory subunits known as cyclins. In order for plants to survive, cell cycle control must be balanced with adaption to dynamic environmental conditions. In this review, we summarize recent advances in our understanding of cell cycle regulation in plants, with a focus on the molecular interactions of cell cycle machinery in the context of stress tolerance. FIGURE 1 | Schematic representation of the mitotic cell cycle in plants.At the G1 phase, D-type cyclins (CYCD) interact with the A-type CDK (CDKA), forming the CDKA/CYCD complex. The activity of CDKA/CYCD complex can be negatively regulated by KPR and SIM proteins. Once activation, this complex phosphorylates RBR to release the transcript factor E2Fa/b-DP. This E2Fa/b-DP complex binds to the E2F box and activate the transcription of S phase genes. At the G2 and M phase S, CYCA and CYCB are strongly expressed and their gene products assemble with CDKA and CDKB. The CYCD can also associate with CDKs. At the beginning of G2 phase, CDK activity are inhibited because of the phosphorylation of Y14 and T15 site by WEEI kinase. The CDC25-related kinase, which removes the inhibitory phosphate groups, still needs to be identified. Once the CDK/CYC complex are active, they phosphorylate MYB3R transcription factors and activate mitotic genes' transcription. Mitotic exit requires anaphase-promoting complex (APC), which degrades cyclins through ubiquitin-proteasome pathway.

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In this study, the V3 and V4 regions of the 16S rRNA gene from metagenomic DNA were sequenced to identify differences in microbial diversity in raw milk of Saanen and Guanzhong goats from the Guanzhong area of China. The results showed that Proteobacteria was the predominant phylum, accounting for 71.31% of all phyla identified in milk from the 2 breeds, and Enterobacter was the predominant genus (24.69%) within the microbial community. Microbial alpha diversity from Saanen goat milk was significantly higher than that of Guanzhong goat milk based on bioinformatic analysis of indices of Chao1, Shannon, Simpson, observed species, and the abundance-based coverage estimator. Functional genes and their likely metabolic pathways were predicted, which demonstrated that the functional genes present in the bacteria in goat milk were enriched in pathways for amino acid metabolism and carbohydrate metabolism, which represented 11.93 and 11.23% of functional genes, respectively. Physicochemical properties such as pH, protein, fat, and AA levels were also determined and correlations made with microbial diversity. We detected a significant difference in the content of lactose and 6 AA, which were higher in Saanen milk than in Guanzhong milk, and positively correlated with microbial carbohydrate metabolism and AA metabolism. Lactococcus, Lactobacillus, Bifidobacterium, Enterococcus, and Streptococcus, which are lactose-utilizing genera, were more abundant in Saanen milk than in Guanzhong milk. Higher levels of lactose in Saanen goat milk may explain its greater microbial diversity. We also demonstrated that most of the AA metabolism-related bacterial genera (e.g., Massilia, Bacteroides, Lysobacter) were enriched in Saanen goat milk. In this research, both probiotic and pathogenic bacteria were identified in goat milk, which provided the microbial information necessary to direct the utilization of beneficial microbial resources and prevent the development of harmful organisms in goat milk.

Vehicular ad hoc networks (VANETs) employ multichannel to provide a variety of safety and non-safety applications. Safety applications require reliable and timely transmission, while non-safety applications need high network throughput. IEEE 802.11p and IEEE 1609.4 protocol divide the bandwidth into seven channels. One control channel (CCH) is to serve safety applications and the other six service channels (SCHs) to serve non-safety applications. The IEEE 1609.4 protocol specifies an alternating scheme to allow vehicles to switch between two types of applications. However, the IEEE 1609.4 multichannel media access control (MAC) protocol has limitations on its capability of supporting either delay-or throughput-sensitive applications. In this paper, we propose an adaptive multi-priority distributed multichannel (APDM) MAC protocol for VANETs. Considering that in realistic VANETs, the queue of MAC layer is far from saturated. We assume that generated packets with different priorities arrive at the MAC layer in a Poisson manner. A Markov analytical model is conducted to optimize the packet transmission probabilities and adjust the ratio between CCH interval and SCH interval dynamically according to the real-time traffic in a distributed way. An M/M/1 queue model is then adopted to analyze the time performance. Extensive simulation results show that the APDM MAC protocol can ensure prioritized transmission of safety packets, reduce the transmission delay of packets and enhance the unsaturated and saturated throughput of SCHs.

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