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Mesona chinensis Benth (MCB) is an important medicinal and edible plant in Southern China and Southeast Asian countries. Chloroplast (cp) genome is usually used for plant phylogeny, species identification, and chloroplast genetic engineering. To characterize the cp genome and determine the evolutionary position and perform the genetic diversity analysis of MCB, we sequence and characterize the MCB cp genome. The results show that the cp genome of MCB is a single circular molecule with a length of 152,635 bp. It is a typical quadripartite structure, comprising a large single-copy region (LSC, 83,514 bp) and a small single-copy region (SSC, 17,751 bp) separated by two inverted repeat regions (IRs, 51,370 bp). It encodes 129 unique genes, including 84 protein-coding genes (PCGs), 37 transfer RNAs (tRNAs), and 8 ribosomal RNAs (rRNAs). Altogether 127 simple sequence repeats (SSRs) are identified in the MCB cp genome with 86.61% of mononucleotide repeats. Phylogenetic analysis reveals that MCB is most closely related to Ocimum basilicum based on the whole cp genomes. Several highly divergent regions are found, such as trnH_psbA, rps16_trnQ, trnS_trnG, trnE_trnT, psaA_ycf3, rpl32_trnL, ccsA_ndhD, ndhG_ndhI, and rps15_ycf1, which can be proposed for use as DNA barcode regions. Genetic diversity analysis unveils a relatively narrow genetic basis of MCB germplasm resources. Therefore, the innovative breeding of MCB is very urgent and necessary in future research.

Mesona chinensis Benth (MCB) (or Platostoma palustre or Platostoma chinense) is an important edible and medicinal plant in China. However, the mitochondrial genome (mitogenome, or mtDNA) of MCB has not been characterized or reported yet. In this study, we first sequenced and characterized the complete mitogenome of MCB. The MCB mitogenome was 494,599 bp in length and encoded 59 genes containing 37 protein-coding genes (PCGs), 19 tRNAs, and 3 rRNAs. Gene transfer analysis revealed that a total of 12 transfer segments with more than 93% identity (total length of 25,427 bp) were detected in the MCB mitogenome. Simple sequence repeats (SSR) analysis showed that 212 simple sequence repeats (SSR) were identified. Repeat sequence analysis revealed 305 repeat sequences (158 forward and 147 palindromic repeats) ranging from 30 bp to 48,383 bp and the 30–39 bp repeats were the majority type. Relative synonymous codon usage (RSCU) analysis uncovered that in total, 9,947 codons were encoding the protein-coding genes (PCGs). Serine (909, 9.1%) and leucine (879, 8.8%) were the two most abundant amino acids, while terminator (32, .3%) was the least abundant amino acid. Ka/Ks analysis indicated that almost all genes were subject to purification selection, except ccmB. Analysis of Lamiaceae mitogenomes constitution revealed that atpB and atpE were unique to the Rotheca serrata and Salvia miltiorrhiza mitogenomes. mttB gene loss was unique to the Boea hygrometrica mitogenome. The core fragments of the Lamiaceae mitogenomes harbored a higher GC content than the specific and variable fragments. In addition, phylogenetic analysis revealed that MCB was closely related to Salvia miltiorrhiza based on the mitogenomes. The current study provided valuable genomic resources for understanding and utilizing this important medicinal plant in the future.

To understand stress response mechanisms, a multiple stress-responsive gene OsPM1 with a disordered region containing about 30 amino acid residues was screened by microarray. Promoter region analysis using PlantCARE showed this gene contains multiple cis-regulatory elements responding to abiotic stresses. Quantitative real-time PCR and promoter-GUS transgenic plant analysis verified that OsPM1 was induced by multiple abiotic stresses. OsPM1-GFP fusion protein expression showed that OsPM1 was localized at the cell membrane. The rice plants overexpressing OsPM1 exhibited hypersensitivity to salt stress but enhanced drought tolerance compared to the wild-type plants; the rice plants expressing antisense of OsPM1 were hyposensitive to salt stress but with weak drought tolerance compared to the wild-type plants. These results showed OsPM1 is a positive regulator of rice tolerance to drought, but it’s also a negative regulator of rice tolerance to salt.

Drought stress affects the normal growth and development of Mesona chinensis Benth (MCB), which is an important medicinal and edible plant in China. To investigate the physiological and molecular mechanisms of drought resistance in MCB, different concentrations of polyethylene glycol 6000 (PEG6000) (0, 5, 10, and 15%) were used to simulate drought conditions in this study. Results showed that the growth of MCB was significantly limited under drought stress conditions. Drought stress induced the increases in the contents of Chla, Chlb, Chla + b, soluble protein, soluble sugar, and soluble pectin and the activities of superoxide dismutase (SOD), catalase (CAT), total antioxidant capacity (TAC), hydrogen peroxide (H2O2), and malondialdehyde (MDA). Transcriptome analysis revealed 3,494 differentially expressed genes (DEGs) (1,961 up-regulated and 1,533 down-regulated) between the control and 15% PEG6000 treatments. These DEGs were identified to be involved in the 10 metabolic pathways, including “plant hormone signal transduction,” “brassinosteroid biosynthesis,” “plant–pathogen interaction,” “MAPK signaling pathway-plant,” “starch and sucrose metabolism,” “pentose and glucuronate interconversions,” “phenylpropanoid biosynthesis,” “galactose metabolism,” “monoterpenoid biosynthesis,” and “ribosome.” In addition, transcription factors (TFs) analysis showed 8 out of 204 TFs, TRINITY_DN3232_c0_g1 [ABA-responsive element (ABRE)-binding transcription factor1, AREB1], TRINITY_DN4161_c0_g1 (auxin response factor, ARF), TRINITY_DN3183_c0_g2 (abscisic acid-insensitive 5-like protein, ABI5), TRINITY_DN28414_c0_g2 (ethylene-responsive transcription factor ERF1b, ERF1b), TRINITY_DN9557_c0_g1 (phytochrome-interacting factor, PIF3), TRINITY_DN11435_c1_g1, TRINITY_DN2608_c0_g1, and TRINITY_DN6742_c0_g1, were closely related to the “plant hormone signal transduction” pathway. Taken together, it was inferred that these pathways and TFs might play important roles in response to drought stress in MCB. The current study provided important information for MCB drought resistance breeding in the future.

To study the effects of light quality and salt stress on RNA editing of Mesona chinensis Benth (MCB) chloroplast genome, the RNA editing sites in the MCB chloroplast protein-coding genes were predicted and then partially verified by PCR and RT-PCR. Meanwhile, the RNA editing efficiency and relative expression of accD, ndhB, ndhF, and rpoB under red and blue light and salt stress conditions were analyzed. A total of 45 editing sites were predicted and all the editing sites were C-to-U conversion. 12 predicted editing sites were verified. The expression level of accD was down-regulated under red light compared with the blue light, as well as down-regulated under salt stress compared with the normal condition (CK). Additionally, the editing efficiency of accD-287 was 96.7% under normal condition, higher than that under salt stress (93.3%) but lower than those under blue and red light (both 100%). In ndhB, ndhB-494 was partially edited under normal growth condition but completely edited under blue and red light and salt stress, and other sites were completely edited under all conditions. It was indicated that the editing frequency was not positively relevant to the transcript level. Besides, accD-287 and ndhB-494 might be involved in response to salt stress.

Drought stress affects the normal growth and development of

Phosphate-induced-1 (PHI-1) and phosphate-induced-1-like family genes respond to plant hormones such as abscisic acid (ABA), BR (brassinosteroid) and ethylene. To date, very few researches have been done on abiotic stress for PHI-1 genes. In this work, we report 12 rice PHI-1 genes through genome-wide analysis. The 12 OsPHI-1 genes were tandemly arranged into two clusters and nine conserved motifs were found among their amino acid sequences. Microarray data indicated that all the OsPHI-1 genes exhibited identical expression level but different expression patterns: most OsPHI-1 genes were expressed intensively in panicle development and responded to IAA and BAP treatments; several OsPHI-1 genes responded to trans-zeatin (tZ) and dimethyl sulfoxide (DMSO) treatments; 11 OsPHI-1 genes showed response to abiotic stress. Furthermore, the promoter region analysis showed that all the OsPHI-1 genes contained cis-regulatory elements responding to abiotic stresses. Our study will be helpful to further investigate the biological functions of PHI-1 genes in rice.

To better understand the mechanisms of plant abiotic stress responses and identify novel stress-related genes in rice, we performed global expression analysis in indica rice Pei'ai 64S under multiple stresses. Among numerous genes, a gene named OsTHIC was selected, which was highly induced in leaves and panicles in response to all stresses at different developmental stages, especially at the booting stage under cold stress. OsTHIC contains an open reading frame (ORF) of 1920 bp and encodes a predicted protein with 639 amino acid residues. The molecular weight and isoelectric point were predicted to be about 71.31 kD and 6.41, respectively. The results of quantitative real-time polymerase chain reaction (qRT-PCR) analysis were almost identical to those from the GeneChip Rice Genome Array. The sequence alignment showed about 99% similarity to rice phosphate methylpyrimidine synthase. Promoter sequence analysis showed that various stress response-related cis-elements were contained in the promoter region. All the results suggested that OsTHIC may be involved in rice stress responses.