ORF355 confers enhanced salinity stress adaptability to S-type cytoplasmic male sterility maize by modulating the mitochondrial metabolic homeostasis.

Moderate stimuli in mitochondria improve wide-ranging stress adaptability in animals, but whether mitochondria play similar roles in plants is largely unknown. Here, we report the enhanced stress adaptability of S-type cytoplasmic male sterility (CMS-S) maize and its association with mild expression of sterilizing gene ORF355. A CMS-S maize line exhibited superior growth potential and higher yield than those of the near-isogenic N-type line in saline fields. Moderate expression of ORF355 induced the accumulation of reactive oxygen species and activated the cellular antioxidative defense system. This adaptive response was mediated by elevation of the nicotinamide adenine dinucleotide concentration and associated metabolic homeostasis. Metabolome analysis revealed broad metabolic changes in CMS-S lines, even in the absence of salinity stress. Metabolic products associated with amino acid metabolism and galactose metabolism were substantially changed, which underpinned the alteration of the antioxidative defense system in CMS-S plants. The results reveal the ORF355-mediated superior stress adaptability in CMS-S maize and might provide an important route to developing salt-tolerant maize varieties.

Comparative analysis of mitochondrial genomes of maize CMS-S subtypes provides new insights into male sterility stability.

BACKGROUND: Cytoplasmic male sterility (CMS) is a trait of economic importance in the production of hybrid seeds. In CMS-S maize, exerted anthers appear frequently in florets of field-grown female populations where only complete male-sterile plants were expected. It has been reported that these reversions are associated with the loss of sterility-conferring regions or other rearrangements in the mitochondrial genome. However, the relationship between mitochondrial function and sterility stability is largely unknown. RESULTS: In this study, we determined the ratio of plants carrying exerted anthers in the population of two CMS-S subtypes. The subtype with a high ratio of exerted anthers was designated as CMS-Sa, and the other with low ratio was designated as CMS-Sb. Through next-generation sequencing, we assembled and compared mitochondrial genomes of two CMS-S subtypes. Phylogenetic analyses revealed strong similarities between the two mitochondrial genomes. The sterility-associated regions, S plasmids, and terminal inverted repeats (TIRs) were intact in both genomes. The two subtypes maintained high transcript levels of the sterility gene orf355 in anther tissue. Most of the functional genes/proteins were identical at the nucleotide sequence and amino acid sequence levels in the two subtypes, except for NADH dehydrogenase subunit 1 (nad1). In the mitochondrial genome of CMS-Sb, a 3.3-kilobase sequence containing nad1-exon1 was absent from the second copy of the 17-kb repeat region. Consequently, we detected two copies of nad1-exon1 in CMS-Sa, but only one copy in CMS-Sb. During pollen development, nad1 transcription and mitochondrial biogenesis were induced in anthers of CMS-Sa, but not in those of CMS-Sb. We suggest that the impaired mitochondrial function in the anthers of CMS-Sb is associated with its more stable sterility. CONCLUSIONS: Comprehensive analyses revealed diversity in terms of the copy number of the mitochondrial gene nad1-exon1 between two subtypes of CMS-S maize. This difference in copy number affected the transcript levels of nad1 and mitochondrial biogenesis in anther tissue, and affected the reversion rate of CMS-S maize. The results of this study suggest the involvement of mitochondrial robustness in modulation of sterility stability in CMS-S maize.

IRREGULAR POLLEN EXINE2 Encodes a GDSL Lipase Essential for Male Fertility in Maize.

Anther cuticle and pollen exine are two physical barriers protecting plant reproductive cells against environmental stresses; defects in either often cause male sterility. Here, we report the characterization of a male-sterile mutant irregular pollen exine2 (ipe2) of maize (Zea mays), which displays shrunken anthers and no starch accumulation in mature pollen grains. We cloned the causal gene IPE2 and confirmed its role in male fertility in maize with a set of complementary experiments. IPE2 is specifically expressed in maize developing anthers during stages 8 to 9 and encodes an endoplasmic-reticulum-localized GDSL lipase. Dysfunction of IPE2 resulted in delayed degeneration of tapetum and middle layer, leading to defective formation of anther cuticle and pollen exine, and complete male sterility. Aliphatic metabolism was greatly altered, with the contents of lipid constituents, especially C16/C18 fatty acids and their derivatives, significantly reduced in ipe2 developing anthers. Our study elucidates GDSL function in anther and pollen development and provides a promising genetic resource for breeding hybrid maize.

RppM, Encoding a Typical CC-NBS-LRR Protein, Confers Resistance to Southern Corn Rust in Maize.

Southern corn rust (SCR) caused by Puccinia polysora Underw. poses a major threat to maize production worldwide. The utilization of host SCR-resistance genes and the cultivation of resistant cultivars are the most effective, economical strategies for controlling SCR. Here, we identified and cloned a new SCR resistance gene, RppM, from the elite maize inbred line Jing2416K. RppM was found to encode a typical CC-NBS-LRR protein localized in both the nucleus and cytoplasm. This gene was constitutively expressed at all developmental stages and in all tissues examined, with the strongest expression detected in leaves at the mature stage. A transcriptome analysis provided further evidence that multiple defense systems were initiated in Jing2416K, including pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity, reinforcement of cell walls, accumulation of antimicrobial compounds, and activation of phytohormone signaling pathways. Finally, we developed functional Kompetitive allele-specific PCR markers for RppM using two conserved SNP sites and successfully applied these functional markers for the detection of RppM and the cultivation of resistant maize cultivars, demonstrating their great potential utility in maize breeding.

Activation of Mitochondrial orf355 Gene Expression by a Nuclear-Encoded DREB Transcription Factor Causes Cytoplasmic Male Sterility in Maize.

Coordination between mitochondria and the nucleus is crucial for fertility determination in plants with cytoplasmic male sterility (CMS). Using yeast one-hybrid screening, we identified a transcription factor, ZmDREB1.7, that is highly expressed in sterile microspores at the large vacuole stage and activates the expression of mitochondria-encoded CMS gene orf355. Δpro, a weak allele of ZmDREB1.7 with the loss of a key unfolded protein response (UPR) motif in the promoter, partially restores male fertility of CMS-S maize. ZmDREB1.7 expression increases rapidly in response to antimycin A treatment, but this response is attenuated in the Δpro allele. Furthermore, we found that expression of orf355 in mitochondria activates mitochondrial retrograde signaling, which in turn induces ZmDREB1.7 expression. Taken together, these findings demonstrate that positive-feedback transcriptional regulation between a nuclear regulator and a mitochondrial CMS gene determines male sterility in maize, providing new insights into nucleus-mitochondria communication in plants.

Evolutionarily conserved DELLA-mediated gibberellin signaling in plants.

Gibberellins (GAs) play important roles in many essential plant growth and development processes. A family of nuclear growth-repressing DELLA proteins is the key component in GA signaling. GA perception is mediated by GID1, and the key event of GA signaling is the degradation of DELLA proteins via the 26S proteasome pathway. DELLA proteins integrating other plant hormones signaling and environmental cue modulating plant growth and development have been revealed. GA turning on the de-DELLA-repressing system is conserved, and independently establishes step-by-step recruitment of GA-stimulated GID1-DELLA interaction and DELLA growth-repression functions during land plant evolution. These discoveries open new prospects for the understanding of GA action and DELLA-mediated signaling in plants.

A PECTIN METHYLESTERASE gene at the maize Ga1 locus confers male function in unilateral cross-incompatibility.

Unilateral cross-incompatibility (UCI) is a unidirectional inter/intra-population reproductive barrier when both parents are self-compatible. Maize Gametophyte factor1 (Ga1) is an intraspecific UCI system and has been utilized in breeding. However, the mechanism underlying maize UCI specificity has remained mysterious for decades. Here, we report the cloning of ZmGa1P, a pollen-expressed PECTIN METHYLESTERASE (PME) gene at the Ga1 locus that can confer the male function in the maize UCI system. Homozygous transgenic plants expressing ZmGa1P in a ga1 background can fertilize Ga1-S plants and can be fertilized by pollen of ga1 plants. ZmGa1P protein is predominantly localized to the apex of growing pollen tubes and may interact with another pollen-specific PME protein, ZmPME10-1, to maintain the state of pectin methylesterification required for pollen tube growth in Ga1-S silks. Our study discloses a PME-mediated UCI mechanism and provides a tool to manipulate hybrid breeding.

MALE STERILE6021 (MS6021) is required for the development of anther cuticle and pollen exine in maize.

The anther cuticle and pollen wall function as physical barriers that protect genetic material from various environmental stresses. The anther cuticle is composed of wax and cutin, the pollen wall includes exine and intine, and the components of the outer exine are collectively called sporopollenin. Other than cuticle wax, cutin and sporopollenin are biopolymers compounds. The precise constituents and developmental mechanism of these biopolymeric are poorly understood. Here, we reported a complete male sterile mutant, male sterile6021, in maize. The mutant displayed a smooth anther surface and irregular pollen wall formation before anthesis, and its tapetum was degraded immaturely. Gas chromatography-mass spectrometry analysis revealed a severe reduction of lipid derivatives in the mutant anther. We cloned the gene by map based cloning. It encoded a fatty acyl carrier protein reductase that was localized in plastids. Expression analysis indicated that MS6021 was mainly expressed in the tapetum and microspore after the microspore was released from the tetrad. Functional complementation of the orthologous Arabidopsis mutant demonstrated that MS6021 is conserved between monocots and dicots and potentially even in flowering plants. MS6021 plays a conserved, essential role in the successful development of anther cuticle and pollen exine in maize.

HBV is a risk factor for poor patient prognosis after curative resection of hepatocellular carcinoma: A retrospective case-control study.

Controversy exists regarding pathological factors affecting the prognosis of hepatocellular carcinoma (HCC) patients with hepatitis B virus (HBV-HCC). Their postoperative clinical behaviors and the exact HBV Deoxyribonucleic Acid (DNA) thresholds that distinguish good and poor prognoses are unknown. This study aimed to compare clinicopathological, pre- and postoperative clinical factors and overall and recurrence-free survival (RFS) between HBV-HCC patients and nonhepatitis B and nonhepatitis C HCC (NBC-HCC) patients to determine the optimal prognostic HBV DNA threshold.Data from 1440 patients with HBV-HCC and NBC-HCC who underwent curative hepatectomy were retrospectively analyzed.Liver function in the HBV-HCC group was significantly worse than in the NBC-HCC group. Compared with NBC-HCC patients, HBV-HCC patients had significantly more vascular invasion and advanced HCC. The HBV-HCC patients also had significantly worse liver function and more complications. Further survival analysis showed significantly lower overall and RFS rates and a higher early recurrence rate in the HBV-HCC group. Univariate analysis indicated that HBV was a risk factor for overall and RFS. Finally, X-tile analysis revealed that the optimal HBV DNA cutoff points for predicting RFS and overall survival in HCC patients were 10,100 and 12,800 IU/mL, respectively.After hepatectomy for HCC, HBV-HCC patients had more complications and a worse prognosis than NBC-HCC patients. Antiviral therapy should be considered before hepatectomy in patients with high (more than approximately 10 IU/mL) HBV DNA levels.

Short- and long-term outcomes of hepatectomy with or without radiofrequency-assist for the treatment of hepatocellular carcinomas: a retrospective comparative cohort study.

The objective of this study was to compare the short- and long-term outcomes of radiofrequency-assisted liver resection (RFLR) and conventional clamp-crushing liver resection (CCLR) and to evaluate the safety and efficiency of RFLR. Between January 2008 and December 2012, a total of 597 patients with hepatocellular carcinoma (HCC) who underwent curative hepatectomy were identified. A total of 272 patients underwent RFLR, and 325 patients received CCLR. The short- and long-term outcomes were compared. The patients in the RFLR and CCLR groups showed similar baseline characteristics. The RFLR group showed less intraoperative blood loss (485.5 vs. 763.2 mL, p = 0.003), a lower transfusion requirement rate (19.1 vs. 31.7%, p ≤ 0.01), shorter surgery duration (211 vs. 296 min, p ≤ 0.01) and a lower vascular inflow occlusion rate (25.7 vs. 33.8%, p = 0.032). No significant postoperative changes in bilirubin or liver enzymes were observed in the two groups. The degree of postoperative complications and morbidity did not significantly differ between the two groups. There were no significant differences in the 1-, 2- and 3-year overall survival rates (73.8%, 58.5%, and 55.7% vs. 80.8%, 65.8%, and 56.2%, respectively) or disease-free rates (51.9%, 47.2%, and 46.0% vs. 54.5%, 44.9%, and 38.5%, respectively) between the RFLR and CCLR groups. These results suggested RFLR was a safe and efficient method for patients with HCC. RFLR was associated with decreased blood loss, fewer blood transfusions, shorter surgery times and less vascular inflow occlusion application. The RFLR group did not show increased liver injury or postoperative morbidity or mortality.

An updated GA signaling 'relief of repression' regulatory model.

Gibberellic acid (GA) regulates many aspects of plant growth and development. The DELLA proteins act to restrain plant growth, and GA relieves this repression by promoting their degradation via the 26S proteasome pathway. The elucidation of the crystalline structure of the GA soluble receptor GID1 protein represents an important breakthrough for understanding the way in which GA is perceived and how it induces the destabilization of the DELLA proteins. Recent advances have revealed that the DELLA proteins are involved in protein-protein interactions within various environmental and hormone signaling pathways. In this review, we highlight our current understanding of the 'relief of repression' model that aims to explain the role of GA and the function of the DELLA proteins, incorporating the many aspects of cross-talk shown to exist in the control of plant development and the response to stress.