Photosynthetic leaf area modulates tiller bud outgrowth in sorghum

Shoot branches or tillers develop from axillary buds. The dormancy versus outgrowth fates of buds depends on genetic, environmental and hormonal signals. Defoliation inhibits bud outgrowth indicating the role of leaf‐derived metabolic factors such as sucrose in bud outgrowth. In this study, the sensitivity of bud outgrowth to selective defoliation was investigated. At 6 d after planting (6 DAP), the first two leaves of sorghum were fully expanded and the third was partially emerged. Therefore, the leaves were selectively defoliated at 6 DAP and the length of the bud in the first leaf axil was measured at 8 DAP. Bud outgrowth was inhibited by defoliation of only 2 cm from the tip of the second leaf blade. The expression of dormancy and sucrose‐starvation marker genes was up‐regulated and cell cycle and sucrose‐inducible genes was down‐regulated during the first 24 h post‐defoliation of the second leaf. At 48 h, the expression of these genes was similar to controls as the defoliated plant recovers. Our results demonstrate that small changes in photosynthetic leaf area affect the propensity of tiller buds for outgrowth. Therefore, variation in leaf area and photosynthetic activity should be included when integrating sucrose into models of shoot branching.     

Phloem exudate metabolic content reflects the response to water-deficit stress in pea plants (Pisum sativum L.)

Drought stress impacts the quality and yield of Pisum sativum. Here, we show how short periods of limited water availability during the vegetative stage of pea alters phloem sap content and how these changes are connected to strategies used by plants to cope with water deficit. We have investigated the metabolic content of phloem sap exudates and explored how this reflects P. sativum physiological and developmental responses to drought. Our data show that drought is accompanied by phloem-mediated redirection of the components that are necessary for cellular respiration and the proper maintenance of carbon/nitrogen balance during stress. The metabolic content of phloem sap reveals a shift from anabolic to catabolic processes as well as the developmental plasticity of P. sativum plants subjected to drought. Our study underlines the importance of phloem-mediated transport for plant adaptation to unfavourable environmental conditions. We also show that phloem exudate analysis can be used as a useful proxy to study stress responses in plants. We propose that the decrease in oleic acid content within phloem sap could be considered as a potential marker of early signalling events mediating drought response.     

孟德尔豌豆基因克隆的研究进展及其在遗传学教学中的应用

150多年前, 孟德尔进行了豌豆7对相对性状的杂交试验, 发现了遗传学的两个基本规律。1900年, 孟德尔定律被重新发现以后, 人们从生理生化、细胞和分子水平等不同层次上对豌豆的这7个性状进行了深入研究。近年, 随着分子生物学技术的发展, 已有种子形状(R)、茎的长度(Le)、子叶颜色(I)和花的颜色(A)等4个性状的基因被克隆; 未成熟豆荚的颜色(Gp)、花的着生位置(Fa)和豆荚形状(V)的基因已被定位在各自的连锁群上。4个孟德尔基因的鉴定和克隆加深了人们对基因概念的理解：如基因功能的多样性、在分子水平上基因变异原因的多样性、显性和隐性的分子实质等。在遗传学教学中, 把孟德尔基因克隆和研究的最新进展介绍给学生, 在分子水平上诠释经典遗传规律, 有助于提高学生的学习兴趣, 帮助学生全面把握从形式遗传学到分子遗传学的内容和遗传学的发展方向。     

Trehalose 6–phosphate coordinates organic and amino acid metabolism with carbon availability

Trehalose 6–phosphate (Tre6P) is an essential signal metabolite in plants, linking growth and development to carbon metabolism. The sucrose–Tre6P nexus model postulates that Tre6P acts as both a signal and negative feedback regulator of sucrose levels. To test this model, short‐term metabolic responses to induced increases in Tre6P levels were investigated in Arabidopsis thaliana plants expressing the Escherichia coli Tre6P synthase gene (otsA) under the control of an ethanol‐inducible promoter. Increased Tre6P levels led to a transient decrease in sucrose content, post‐translational activation of nitrate reductase and phosphoenolpyruvate carboxylase, and increased levels of organic and amino acids. Radio‐isotope (¹⁴CO₂) and stable isotope (¹³CO₂) labelling experiments showed no change in the rates of photoassimilate export in plants with elevated Tre6P, but increased labelling of organic acids. We conclude that high Tre6P levels decrease sucrose levels by stimulating nitrate assimilation and anaplerotic synthesis of organic acids, thereby diverting photoassimilates away from sucrose to generate carbon skeletons and fixed nitrogen for amino acid synthesis. These results are consistent with the sucrose–Tre6P nexus model, and implicate Tre6P in coordinating carbon and nitrogen metabolism in plants.     

苹果MdPEPC基因家族鉴定及在腋芽萌发中的作用

磷酸烯醇式丙酮酸羧化酶（phosphoenolpyruvate carboxykinase,PEPC）家族蛋白普遍存在各种植物中,在光合碳同化过程中起到重要作用,同时具有多种非光合生物学功能,但PEPC基因在苹果（Malus domestica Borkh.）中尚未研究报道。本研究以苹果新基因组数据为基础,利用生物信息学方法对苹果PEPC家族成员（the members of apple PEPC family,MdPEPC）进行鉴定,并对其在不同组织中的表达谱以及去顶和细胞分裂素噻重氮苯基脲（thidazuron,TDZ）处理后苹果腋芽转录组中的表达模式进行分析,以期探究MdPEPC基因在参与苹果腋芽萌发中的作用。结果表明,苹果MdPEPC家族共有6个成员,分布于6条不同的染色体上,且理化特征较为相似;系统进化树及序列比对分析显示其可分为2个亚组（Group Ⅰ和Group Ⅱ）,其中Ⅰ组含4个MdPEPC家族成员,属于植物型PEPCs,而MdPEPC4和MdPEPC5则与拟南芥细菌型AtPPC4聚类到Ⅱ组;共线性分析表明,MdPEPC成员之间不存在串联重复,含7对片段重复;顺式作用元件分析显示,MdPEPC家族成员不仅受光和逆境等影响,还受多种激素综合调控;表达谱显示,除MdPEPC4和MdPEPC5外,其他植物型MdPEPC在不同组织中均有表达。转录组数据分析表明,去顶和TDZ处理后MdPEPC1和MdPEPC3表达量上调,而MdPEPC2则在处理后48 h明显下调表达。综上所述,本研究通过对苹果MdPEPC家族的鉴定和分析,筛选出MdPEPC1、MdPEPC2和MdPEPC3作为调控苹果腋芽萌发的候选基因,以便后期对其进行深入研究。     

Two isoforms of the GBSSI class of granule-bound starch synthase are differentially expressed in the pea plant (Pisum sativum L.)

In addition to the GBSSI isoform of starch synthase described previously, the pea plant contains a second, granule-bound isoform, GBSSIb. GBSSI is abundant in pea embryos and Rhizobium root nodules, is present at low levels in pods and is absent from leaves. Mutations at the lam locus eliminate GBSSI from all of these organs. GBSSIb is present in pods, leaves and nodules and is unaffected by mutations at the lam locus. GBSSI and GBSSIb are very similar in molecular mass, primary sequence, activity and antigenic properties. GBSSIb, like GBSSI, can synthesize amylose in the presence of malto-oligosaccharides in isolated starch granules. However, its role in vivo is unclear. The lam mutation eliminates amylose from the starch of embryos but does not affect the relatively small amounts of amylose-like material in the starch of pods, leaves and nodules. The significance of these results for understanding of the regulation of amylose synthesis is discussed.     

Endogenous levels of abscisic acid,indole-3-acetic acid and benzyladenine during in vitro bud growth induction of Wild cherry (Prunus avium L.)

Levels of endogenous growth substances (abscisic acid: ABA; indole-3-acetic acid: IAA) and applied benzyladenine (BA) were quantified during the eight first days of in vitro propagation of Wild Cherry (Prunus avium L.). Axillary buds from the middle part of the explants started to grow at day 2, thus were released from apical dominance. Hormone levels were measured in the apical, median and basal parts of the explants using an avidin-biotin based enzyme-linked immunosorbent assay (ELISA) after a purification of the extracts by high performance liquid chromatography (HPLC). All hormones showed rapid and considerable changes during the first eight days of growth. Exogenous IBA was probably transformed into IAA mainly in the basal part of the explant, and BA penetrated quickly. ABA levels were transiently enhanced in the apical part of the explants bearing young leaves. These phenomena are discussed in connection with the axillary bud reactivation.     

Water potential, turgor and cell wall properties in elongating tissues of the hydrotropically bending roots of pea (Pisum sativum L.)

The hydrotropic bending of roots of an ageotropic pea mutant, ageotropum, was studied in humid air in a chamber with a steady humidity gradient. We examined the effects of atmospheric humidity around the root on the water status of root tissues, as well as the wall growth and the hydraulic properties of the elongating tissues. Atmospheric humidity at the surface of the root was clearly lower on the side orientated towards the air with lower humidity than on the side orientated towards the air with higher humidity. However, there were no differences in water potential and osmotic potential between the tissues that faced air with higher and lower humidities in the elongating and mature regions. Plastic extensibility was higher in the tissues that faced the air with lower humidity than in the tissues that faced the air with higher humidity. No differences in turgor pressure and yield threshold were observed between the tissues that faced air with higher and lower humidities. Therefore, the extensibility of the cell wall appeared to be responsible for the different growth rates of tissues in root hydrotropism. A further probable cause of the hydrotropical bending of roots is changes in the hydraulic conductance in the elongating tissues. Since the hydrotropic bending of roots occurred only when a root tip was exposed to a humidity gradient, hydrotropism might occur after perception of a difference in humidity by the root tip, with accompanying changes in cell wall extensibility and hydraulic conductance.     

Quaternary variations in the structural assembly of N‐acetylglucosamine‐6‐phosphate deacetylase from Pasteurella multocida

N‐acetylglucosamine 6‐phosphate deacetylase (NagA) catalyzes the conversion of N‐acetylglucosamine‐6‐phosphate to glucosamine‐6‐phosphate in amino sugar catabolism. This conversion is an essential step in the catabolism of sialic acid in several pathogenic bacteria, including Pasteurella multocida, and thus NagA is identified as a potential drug target. Here, we report the unique structural features of NagA from P. multocida (PmNagA) resolved to 1.95 Å. PmNagA displays an altered quaternary architecture with unique interface interactions compared to its close homolog, the Escherichia coli NagA (EcNagA). We confirmed that the altered quaternary structure is not a crystallographic artifact using single particle electron cryo‐microscopy. Analysis of the determined crystal structure reveals a set of hot‐spot residues involved in novel interactions at the dimer‐dimer interface. PmNagA binds to one Zn²⁺ ion in the active site and demonstrates kinetic parameters comparable to other bacterial homologs. Kinetic studies reveal that at high substrate concentrations (~10‐fold the K_M), the tetrameric PmNagA displays hysteresis similar to its distant neighbor, the dimeric Staphylococcus aureus NagA (SaNagA). Our findings provide key information on structural and functional properties of NagA in P. multocida that could be utilized to design novel antibacterials.     

Cytosolic glyceraldehyde‐3‐phosphate dehydrogenases play crucial roles in controlling cold‐induced sweetening and apical dominance of potato (Solanum tuberosum L.) tubers

Glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) is an important enzyme that functions in producing energy and supplying intermediates for cellular metabolism. Recent researches indicate that GAPDHs have multiple functions beside glycolysis. However, little information is available for functions of GAPDHs in potato. Here, we identified 4 putative cytosolic GAPDH genes in potato genome and demonstrated that the StGAPC1, StGAPC2, and StGAPC3, which are constitutively expressed in potato tissues and cold inducible in tubers, encode active cytosolic GAPDHs. Cosuppression of these 3 GAPC genes resulted in low tuber GAPDH activity, consequently the accumulation of reducing sugars in cold stored tubers by altering the tuber metabolite pool sizes favoring the sucrose pathway. Furthermore, GAPCs‐silenced tubers exhibited a loss of apical dominance dependent on cell death of tuber apical bud meristem (TAB‐meristem). It was also confirmed that StGAPC1, StGAPC2, and StGAPC3 interacted with the autophagy‐related protein 3 (ATG3), implying that the occurrence of cell death in TAB‐meristem could be induced by ATG3 associated events. Collectively, the present research evidences first that the GAPC genes play crucial roles in diverse physiological and developmental processes in potato tubers.     

RNA interference of a trehalose-6-phosphate synthase gene reveals its roles in the biosynthesis of chitin and lipids in Heortia vitessoides(Lepidoptera:Crambidae)

Trehalose 6-phosphate synthase(TPS),an enzyme that hydrolyzes two glucose molecules to yield trchalose,plays a pivotal role in various physiological processes.In this study,we cloned the trehalose-6-phosphate synthase gene(HvTPS)and investigated its expression patterns in various tssues and d:velopmental stages in Heortia vitessoides Moore(Lepidoptera:Crambidac).HvTPS was highly expressed in the fat body and after pupation or before molting.We knocked down TPS in H.vitessoides by RNA interference and found that 3.0μg of dsHvTPS resulted in optimal interference at 24 h and 36 h post-injection and caused a sharp decline in the survival rate during the 5th instar larval-pupal stage and obviously abnormal or lethal phenotypes.Additionally.compared to the controls,TPS activity and trehalose contents were significantly lower and the glucose content was significantly higher 24 h or 36 h after injection with 3.0μg of dsHIvTPS.Furthermore,the silencing of HvTPS suppressed the cxpression of six key genecs in the chitin biosynthesis pathway and one key gene related to lipid catabolism.The expression levels of two genes associated with lipid biosynthesis were upregulated.These results strongly suggest that HvTPS is essential for the normal growth and development of H.vitessoides and provide a reference for further studies of the utility of key genes involved in chitin and lipid biosynthesis for controlling insect development.     

Glucose‐6‐phosphate dehydrogenase is posttranslationally regulated in the larvae of the freeze‐tolerant gall fly,Eurosta solidaginis,in response to freezing

The freeze‐tolerant larvae of the goldenrod gall fly (Eurosta solidaginis) undergo substantial alterations to their molecular physiology during the winter including the production of elevated quantities of glycerol and sorbitol, which function as cryoprotectants to survive whole body freezing. Production of these cryoprotectants depends on cytosolic pools of nicotinamide adenine dinucleotide phosphate H (NADPH), a major source being the pentose phosphate pathway (PPP). Glucose‐6‐phosphate dehydrogenase (G6PDH) mediates the rate‐limiting and committed step of the PPP and therefore its molecular properties were explored in larvae sampled from control versus frozen states. G6PDH was purified from control (5°C) and frozen (?15°C) E. solidaginis larvae by a single‐step chromatography method utilizing 2′,5′‐ADP agarose and analyzed to determine its enzymatic parameters. Studies revealed a decrease in K_m for G6P in the frozen animals (to 50% of control values) suggesting an increased flux through the PPP. Immunoblotting of the purified enzyme showed differences in the relative extent of several posttranslational modifications, notably ubiquitination (95% decrease in frozen larvae), cysteine nitrosylation (61% decrease), threonine (4.1 fold increase), and serine phosphorylation (59% decrease). Together these data suggested that the increased flux through the PPP needed to generate NADPH for cryoprotectants synthesis is regulated, at least in part, through posttranslational alterations of G6PDH.     

Toward understanding the key enzymes involved in β‐poly (L‐malic acid) biosynthesis by Aureobasidium pullulans ipe‐1

β‐poly (L‐malic acid) (PMLA) is a biopolyester which has attracted industrial interest for its potential application in medicine and other industries. A high dissolved oxygen concentration (DO) was beneficial for PMLA production, while the mechanisms of DO in PMLA biosynthesis by Aureobasidium pullulans are still poorly understood. In this work, the amount of PMLA was first compared when A. pullulans ipe‐1 were cultured under a high DO level (70% saturation) and a low DO level (10% saturation). Meanwhile, the key enzymes involved in different pathways of the precursor L‐malic acid biosynthesis were studied. The results revealed that the activities of glucose‐6‐phosphate dehydrogenase (G6PDH) and phosphoenolpyruvate carboxylase (PEPC) were positively correlated with cell growth and PMLA production, while the activities of phosphofructokinases (PFK), pyruvic carboxylase (PC) and citrate synthetase (CS) did no show such correlations. It indicated that the Pentose Phosphate Pathway (PPP) may play a vital role in cell growth and PMLA biosynthesis. Moreover, the precursor L‐malic acid for PMLA biosynthesis was mainly biosynthesized through phosphoenolpyruvic acid (PEP) via oxaloacetate catalyzed by PEPC. It was also found that low concentration of sodium fluoride (NaF) might impel carbon flux flow to the oxaloacetate through PEP, but inhibit the flux to the oxaloacetate via pyruvic acid.