Chromosome-level assembly of triploid genome of Sichuan pepper(Zanthoxylum armatum)

As an important spice species in Rutaceae, the Sichuan pepper (Zanthoxylum armatum) can provide pungent and numbing taste, as well as aroma in its mature fruit. Here we assembled a chromosome-level genome of green prickly ash which was widely cultivated in a major production area including Chongqing and Sichuan province, China. We generated 712 Gb (~112×) PacBio long reads and 511 Gb (~82×) Hi-C data, and yielded an assembly of 99 pseudochromosomes with total size of 5.32 Gb and contig N50 of 796 kb. The genomic analyses and cytogenetic experiments both indicated that the cultivarZhuye Huajiao’ was a triploid. We identified a Zanthoxylum-specific whole genome duplication event emerging about 24.8 million years ago (Mya). We also detected a transposition burst event (0.3-0.4 Mya) responsible for the large genome size of Z. armatum. Metabolomic analysis of the Zanthoxylum fruits during development stages revealed profiles of39 volatile aroma compounds and 528 secondary metabolites, from which six types of sanshools were identified. Based on metabolomic and transcriptomic network analysis, we screened candidate genes encoding long chain acyl-CoA synthetase, fatty acid desaturase,branched-chain amino acid aminotransferase involved in sanshool biosynthesis and three genes encoding terpene synthase during fruit development. The multi-omics data provide insights into the evolution of Zanthoxylum and molecular basis of numbing and aroma flavor of Sichuan pepper.

Effect of low-nitrogen stress on photosynthesis and chlorophyll fluorescence characteristics of maize cultivars with different low-nitrogen tolerances

Nitrogen(N)is a critical element for plant growth and productivity that influences photosynthesis and chlorophyll fluorescence.We investigated the effect of low-N stress on leaf photosynthesis and chlorophyll fluorescence characteristics of maize cultivars with difference in tolerance to low N levels.The low-N tolerant cultivar ZH311 and low-N sensitive cultivar XY508 were used as the test materials.A field experiment(with three N levels:N0,0 kg ha–1;N1,150 kg ha–1;N2,300 kg ha–1)in Jiyanyang,Sichuan Province,China,and a hydroponic experiment(with two N levels:CK,4 mmol L–1;LN,0.04 mmol L–1)in Chengdu,Sichuan Province,China were conducted.Low-N stress significantly decreased chlorophyll content and rapid light response curves of the maximum fluorescence under light(Fm′),fluorescence instable state(Fs),non-photochemical quenching(qN),the maximum efficiency of PSII photochemistry under dark-adaption(Fv/Fm),potential activity of PSII(Fv/Fo),and actual photochemical efficiency of PSII(ΦPSII)of leaves.Further,it increased the chlorophyll(Chl)a/Chl b values and so on.The light compensation point of ZH311 decreased,while that of XY508 increased.The degree of variation of these indices in low-N tolerant cultivars was lower than that in low-N sensitive cultivars,especially at the seedling stage.Maize could increase Chl a/Chl b,apparent quantum yield and light saturation point to adapt to N stress.Compared to low-N sensitive cultivars,low-N tolerant cultivars maintained a higher net photosynthetic rate and electron transport rate to maintain stronger PSII activity,which further promoted the ability to harvest and transfer light.This might be a photosynthetic mechanism by which low-N tolerant cultivar adapt to low-N stress.

Grain-filling characteristics and yield differences of maize cultivars with contrasting nitrogen efficiencies

To investigate the effect of nitrogen management on the grain-filling characteristics and yield formation of maize cultivars with contrasting nitrogen efficiencies,and to identify differences in grain-filling characteristics and yield of maize cultivars in response to nitrogen management,a two-year field experiment was conducted in southwest China in2015–2016.The grain-filling rate and duration of the N-inefficient cultivar XY 508 were higher than those of the N-efficient cultivar ZH 311.The 100-kernel weight of XY 508 was significantly higher than that of ZH 311.The kernel number per ear of ZH 311 was significantly higher than that of XY 508,making the population filling rate of ZH 311 significantly higher than that of XY 508.The higher population filling rate of the N-efficient maize cultivar led to a significant yield advantage over the N-inefficient maize cultivar.Nitrogen management effectively improved maize grain yield,but the response of maize cultivars with contrasting nitrogen efficiencies to nitrogen management was inconsistent.A basal fertilizer ratio 60.43%with a topdressing ratio 39.57%effectively increased grainfilling rate,delayed the time to maximum filling rate,prolonged the active filling period and effective grain-filling time,increased the 100-kernel weight,and maintained higher kernels per ear,thereby improving the population filling rate and maximizing the yield advantage of the N-efficient cultivar.A 100%basal fertilizer ratio not only increased the number of kernels per ear,but also maintained high grain filling characteristics to obtain a higher 100-kernel weight and increased the population filling rate,leading to a high grain yield in the N-inefficient cultivar.Thus,the 100%basal fertilizer ratio partially compensated for the deficient grain yield of the N-inefficient cultivar.

Cloning of the ZoWRKY1 Gene and its Correlation with 6-gingerol Biosynthesis in Zingiber officinale Roscoe

Ginger(Zingiber officinale Roscoe)has high economic value as medicinal and food resources.6-gingerol is the core medicinal constituents of ginger.In the present study,a local ginger cultivar of Chongqing was taken as the research material.The ZoWRKY1 gene was cloned to determine its expression level in different ginger developmental phases and to analyze its correlation with 6-gingerol content.The expression level of ZoWRKY1 under different concentrations of NaCl stress was tested,and so was the correlation between ZoWRKY1’s expression level and the contents of 6-gingerol synthase genes,i.e.ZoPAL,ZoC4H and Zo4CL.The results showed that the cDNA of the cloned ZoWRKY1 gene is 1026 bp in total length,and ZoWRKY1 belongs to the second type member of the WRKY family;the expression level of ZoWRKY1 rose sharply in the second developmental phase of the ginger which was about one month after sowing,and there was a significant correlation between the expression level of ZoWRKY1 and the increase of 6-gingerol content;the expressions of ZoWRKY1 and 6-gingerol synthase genes ZoPAL,ZoC4H and Zo4CL had sharp rises under 25 g/L NaCl stress,and the expression level of ZoWRKY1 was closely related to that of ZoC4H or Zo4CL.Therefore,it was speculated that there was a regulatory correlation between ZoWRKY1 and ZoC4H or Zo4CL that can further affect the biosynthesis of 6-gingerol.

Nitrogen application affects maize grain filling by regulating grain water relations

Grain water relations play an important role in grain filling in maize. The study aimed to gain a clear understanding of the changes in grain dry weight and water relations in maize grains by using hybrids with contrasting nitrogen efficiencies under differing nitrogen levels. The objectives were: 1) to understand the changes in dry matter and percent moisture content(MC) during grain development in response to different nitrogen application rates and 2) to determine whether nitrogen application affects grain filling by regulating grain water relations. Two maize hybrids, high N-efficient Zhenghong 311(ZH311) and low N-efficient Xianyu 508(XY508), were grown in the field under four levels of N fertilizer: 0, 150, 300, and 450 kg N ha;during three growing seasons. Dry weight, percent MC and water content(WC) of basal-middle and apical grains were investigated. The difference in the maximum WC and filling duration of basal-middle and apical grains in maize ears resulted in a significant difference in final grain weight. Grain position markedly influenced grain drying down;specifically, the drying down rate of apical grains was faster than that of basal-middle grains. Genotype and grain position both influenced the impact of nitrogen application rate on grain filling and drying down. Nitrogen rate determined the maximum grain WC and percent MC loss rate in the middle and the late grain-filling stages, thus affecting final grain weight. The use of high N-efficient hybrids, combined with the reduction of nitrogen application rate, can coordinate basal-middle and apical grain drying down to ensure yield. This management strategy could lead to a win-win situation in which the maximum maize yield, efficient mechanical harvest and environmental safety are all achieved.