Phenylalanine ammonia-lyase gene families in cucurbit species: Structure, evolution, and expression

Phenylalanine ammonia-lyase （PAL）, the first enzyme of phenylpropanoid pathway, is always encoded by multigene families in plants. In this study, using genome-wide searches, 13 PAL genes in cucumber （CsPAL1-13） and 13 PALs in melon （Cm- PALl-13） were identified. In the corresponding genomes, ten of these PAL genes were located in tandem in two clusters, while the others were widely dispersed in different chromosomes as a single copy. The protein sequences of CsPALs and CmPALs shared an overall high identity to each other. In our previous report, 12 PAL genes were identified in watermelon （CIPAL1-12）. Thereby, a total of 38 cucurbit PAL members were included. Here, a comprehensive comparison of PAL gene families was performed among three cucurbit plants. The phylogenetic and syntenic analyses placed the cucurbit PALs as 11 CsPAL-CmPAL-CIPAL triples, of which ten triples were clustered into the dicot group, and the remaining one, CsPAL1-CmPAL8-CIPAL2, was grouped with gymnosperm PALs and might serve as an ancestor of cucurbit PALs. By comparing the syntenic relationships and gene structure of these PAL genes, the expansion of cucurbit PAL families might arise from a series of segmental and tandem duplications and intron insertion events. Furthermore, the expression profiling in different tissues suggested that different cucurbit PALs displayed divergent but overlapping expression profiles, and the CsPAL-CmPAL-CIPAL orthologs showed correlative expression patterns among three cucurbit plants. Taken together, this study provided an extensive description on the evolution and expression of cucurbit PAL gene families and might facilitate the further studies for elucidating the functions of PALs in cucurbit plants.

Genetic diversity and population structure analysis of Pistacia species revealed by phenylalanine ammonia-lyase gene markers and implications for conservation

Information on population genetic structure and crop genetic diversity is important for genetically improving crop species and conserving threatened species. The PAL gene sequence is part of a multigene family that can be utilized to design DNA marker systems for genetic diversity and population structure investigation. In the current study, genetic diversity and population structure of 100 accessions of wild Pistacia species were investigated with 78 PAL markers. A protocol for using PAL sequences as DNA markers was developed. A total of 313 PAL loci were recognized, showing 100% polymorphism for PAL markers. The PAL markers produced relatively more observed and effective alleles in Pistacia falcata and Pistacia atlantica, with a higher Shannon＇s information index and expected heterozygosity in P. atlantica, Pistacia vera and Pistacia mutica. Pairwise assessment of Nei＇s genetic distance and genetic identity between populations revealed a close association between geographically iso- lated populations of Pistacia khinjuk and Pistacia chinensis. The accessions of wild Pistacia species had more genetic relationship among studied groups of species. Analysis of molecular variance indicated 19% among- population variation and 81% within-population variation for the PAL gene based DNA marker. Population structure analysis based on PAL revealed four groups with high genetic admixture among populations. The results establish PAL markers as a functional DNA marker system and provide important genetic information about accessions from wild populations of Pistacia species.

Identification of PAL genes related to anthocyanin synthesis in tea plants and its correlation with anthocyanin content

The phenylalanine ammonia-lyase(PAL)gene family in tea plants(Camellia sinensis L.)encodes the enzyme that catalyzes the first reaction of the phenylpropane metabolic pathway.The present study aimed to characterize the PAL genes in tea plants,and get better insights on the CsPALs in anthocyanins accumulation.Seven CsPAL genes were identified and characterized in tea plants by bioinformatics analysis.Systematic analysis of CsPALs was conducted for its phylogenetic relationship,gene structure,chromosomal location,and protein conserved motifs based on tea plant genome.The cis-elements of CsPALs were responsive to light,abiotic stress,hormone,and MYB-binding site.Furthermore,tissuespecific expression analysis showed that CsPAL4 was expressed preferentially in young leaves and buds.Correlation analysis was performed in purple-leaf tea with anthocyanin components,and it was suggested that CsPAL4 was closely related with different anthocyanin accumulated,especially with cyanidin 3-O-galactoside,cyanidin 3-O-glucoside,and delphinidin 3-O-glucoside.Additionally,the putative upstream regulation factors CsMYBs(CsMYB59,CsARR1,CsSRM1,CsMYB101,and CsMYB52)and CsbHLHs(CsbHLH104,CsbHLH3,CsbIM1,CsTCP14,and CsPIF4)could bind to the promoter of CsPALs,thereby activating its transcription.This study provides a theoretical basis for further research to elucidate the functions of the CsPAL genes.

Overexpression of IbPAL1 promotes chlorogenic acid biosynthesis in sweetpotato

Sweetpotato[Ipomoea batatas(L.)Lam.],a food crop with both nutritional and medicinal uses,plays essential roles in food security and health-promoting.Chlorogenic acid(CGA),a polyphenol displaying several bioactivities,is distributed in all edible parts of sweetpotato.However,little is known about the specific metabolism of CGA in sweetpotato.In this study,IbPAL1,which encodes an endoplasmic reticulum-localized phenylalanine ammonia lyase(PAL),was isolated and characterized in sweetpotato.CGA accumulation was positively associated with the expression pattern of IbPAL1 in a tissue-specific manner,as further demonstrated by overexpression of IbPAL1.Overexpression of IbPAL1 promoted CGA accumulation and biosynthetic pathway genes expression in leaves,stimulated secondary xylem cell expansion in stems,and inhibited storage root formation.Our results support a potential role for IbPAL1 in sweetpotato CGA biosynthesis and establish a theoretical foundation for detailed mechanism research and nutrient improvement in sweetpotato breeding programs.

象草不同品种木质素合成关键酶活性的动态变化

以MT-1象草(Pennisetum purpureumcv.MT-1)及其近缘品种为研究对象,通过在2008年3月、5月、7月、8月、10月和12月的6次取样,对其茎秆的苯丙氨酸解氨酶(PAL)和4-香豆酸:辅酶A连接酶(4CL)的酶活性动态变化规律进行研究,从而为MT-1象草新品种的推出提供帮助。结果表明:MT-1、N51、Mott和Guimu No.1象草茎秆PAL酶活性的最大值均出现在7月,Huanan象草PAL酶活性的最大值出现在5月,这与它们木质素含量的快速增长期相吻合;最小值出现的月份各不相同,又反映了品种间的差异。5个品种(系)茎秆4CL活性在5月份达到最大值,出现在木质素含量快速增长的前期(快速拔节的前期);从7月开始大幅度降低,其中MT-1、N51、Huanan和Guimu No.1象草在10月又出现一个小的峰值;Mott象草则在12月又出现一个差异不显著的小高峰,这与其延迟的成熟期密切相关。

Active changes of lignification-related enzymes in pepper response to Glomus intraradices and/or Phytophthora capsici

The activities of enzymes responsible for lignification in pepper, pre-inoculation with arbuscular mycorrhizal (AM) fungus of Glomus intraradices and/or infection with pathogenic strain of Phytophthora capsici, and the biological control effect of G. intraradices on Phytophthora blight in pepper were investigated. The experiment was carried out with four treatments: (1) plants pre-inoculated with G. intraradices (Gi), (2) plants pre-inoculated with G. intraradices and then infected with P. capsici (Gi+Pc), (3) plants infected with P. capsici (Pc), and (4) plants without any of the two microorganisms (C). Mycorrhizal coloni-zation rate was reduced by about 10% in pathogen challenged plants. Root mortality caused by infection of P. capsici was com-pletely eliminated by pre-inoculation with antagonistic G. intraradices. On the ninth day after pathogen infection, Peroxidase (POD) activity increased by 116.9% in Pc-treated roots but by only 21.2% in Gi+Pc-treated roots, compared with the control, respectively. Polyphenol oxidase (PPO) and Phenylalanine ammonia-lyase (PAL) activities gradually increased during the first 3 d and dramatically decreased in Pc-treated roots but slightly decreased in Gi+Pc-treated roots, respectively. On the ninth day after pathogen infection, PPO and PAL decreased by 62.8% and 73.9% in Pc-treated roots but by only 19.8% and 19.5% in Gi+Pc-treated roots, compared with the control, respectively. Three major POD isozymes (45 000, 53 000 and 114 000) were present in Pc-treated roots, while two major bands (53 000 and 114 000) and one minor band (45 000) were present in spectra of Gi+Pc-treated roots, the 45 000 POD isozyme was significantly suppressed by G. intraradices, suggesting that the 45 000 POD isozyme was induced by the pathogen infection but not induced by the antagonistic G. intraradices. A 60 000 PPO isozyme was induced in Pc-treated roots but not induced in Gi+Pc-treated roots. All these results showed the inoculation of antagonistic G. intraradices alleviates root mortality, activates changes of lignification-related enzymes and induces some of the isozymes in pepper plants infected by P. capsici. The results suggested that G. intraradices is a potentially effective protection agent against P. capsici.