Nutrient content and resorption efficiency of leaves of broad-leaved trees along altitudes in Wuyi Mountains, China.

To reveal the variation of leaf nutrient utilization strategies with altitude gradient in subtropical mountain broadleaved trees, 44 species of broadleaved trees at different altitudes (1400, 1600 and 1800 m) in Wuyi Mountains were selected to measure nutrient content, stoichiometric ratio, and nutrient resorption efficiency of green and senescent leaves, and analyzed their allometric growth relationships. The results showed that nitrogen (N) and phosphorus (P) contents in green leaves were significantly higher than those in senescent leaves, which increased with the increases of altitude. The average values of phosphorus resorption efficiency (PRE) and nitrogen resorption efficiency (NRE) were 48.3% and 34.9%, respectively. PRE was significantly higher than NRE. There was no significant difference in nutrient resorption efficiency with altitude. NRE had positive isokinetic growth with and mature leaf N content at low altitude (1400 m) and negative allometry growth with senescent leaf N content at high altitude (1800 m). PRE and N and P contents of senescent leaves had negative isokinetic growth at low altitude (1400 m) and negative allometry growth at high altitudes (1600 and 1800 m). PRE-NRE allometric growth index was 0.95 at each altitude. The nutrient contents of green and senescent leaves increased with the increases of altitude, but altitude did not affect nutrient resorption efficiency. Plants preferred to re-absorbed P from senescent leaves. Nutrient resorption efficiency of leaves at high altitude affected the nutrient status of senescent leaves.

Genome-wide analysis of the SMXL gene family in common bean and identification of karrikin-responsive PvSMXL2 as a negative regulator of PEG-induced drought stress.

Common bean (Phaseolus vulgaris L.) is a major legume crop worldwide, but its growth and development frequently face challenges due to abiotic stresses, particularly drought. Proper supplement of copper could mitigate the adverse effects of drought, but excessive accumulation of this metal in plants can be harmful. The suppressor of MAX2 1-like (SMXL) gene family, which plays important roles in various plant processes, including stress responses, remains poorly understood in common bean. In this study, we identified nine orthologues of SMXL genes in common bean, which are located on six chromosomes and classified into four subgroups. Basic molecular properties, including theoretical isoelectric point (PI), molecular weight (MW), grand average of hydropathicity (GVIO), gene structure, and conserved motifs were characterized, and numerous cis-elements in promoters were predicted. The expression patterns of PvSMXL genes were found to be distinct under 10% polyethylene glycol (PEG)-induced drought stress and 200 µM Cu treatments. Most PvSMXLs showed reduced expression in response to Cu treatment, whereas nearly half PvSMXLs exhibited inducible expression under drought stress. PvSMXL2, which exhibited a rapid response to karrikin 1 (KAR1), an active form of the plant growth regulators newly found in the smoke of burning plant material, was down-regulated by both PEG-induced drought and Cu stresses. Transient silencing of PvSMXL2 resulted in enhanced drought stress tolerance without conferring Cu tolerance. These findings provide valuable insights into the functions of SMXL genes in common bean under abiotic stress conditions.

Gynura japonica: A new host of Apple stem grooving virus and Chrysanthemum virus B in China.

Gynura japonica (Thunb.) Juel [Asteraceae; syn: G. segetum (Lour.) Merr] is an important perennial medicinal herb used in China for topical treatment of trauma injuries (Lin et al. 2003). It grows naturally in the southern provinces of China and is also sometimes cultivated. During 2018-2020, wild G. japonica plants exhibiting chlorotic spots and mosaic symptoms were observed in Zhejiang province, China. To identify the possible causal agents of the disease, a single symptomatic leaf sample was collected in August 2019 and sent to Zhejiang Academy of Agricultural Sciences (Hangzhou, China) for next generation sequencing (NGS). Total RNAs extracted with TRIzol (Invitrogen, Carlsbad, USA) were subjected to high throughput sequencing on the Illumina NovaSeq 6000 platform with PE150bp and data analysis was performed by CLC Genomic Workbench 11 with default parameters (QIAGEN, Hilden, Germany). A total of 37,314,080 paired-end reads were obtained, and 11,785 contigs (961 to 10,964 bp) were generated and compared with sequences in GenBank using BLASTn or BLASTx. Of the total of 12 viral-related contigs obtained, one with a length of 6,442 nt mapped to the genomic RNA of ASGV (MN495979), seven contigs with lengths ranging from 1,034 to 2,901 nt mapped to Chrysanthemum virus B (CVB), and four mapped to broad bean wilt virus 2 (BBWV2), a virus which is known to infect G. procumbens (Kwak et al. 2017). To further confirm the presence of ASGV and CVB, primers were designed and the complete nucleotide sequences of both viruses were amplified from the original NGS sample using reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) according to the manufacturer's instructions (Tiosbio, Beijing, China). BLASTn analysis revealed that the complete 6,451 nt sequence of ASGV (GenBank accession No. MW259059) shared the highest identity (81.2%) with a Chinese isolate of ASGV from citrus (MN495979). The two isolates grouped with another Chinese isolate (from pear) in phylogenetic analysis. The predicted coat protein of the virus had the highest nt identity of 93.7% (96.2% amino acid sequence identity) with that of the Chinese ASGV isolate XY from apple (KX686100). The complete genomes of two distinct molecular variants of CVB (both 8,987 nt in length) were also obtained from this sample (GenBank accession Nos. MW269552, MW269553). They shared 86.8% nt identity with each other and had 81.1% and 82.1% identity to the only known complete sequence of CVB from chrysanthemum (AB245142). Ten additional wild G. japonica plants with mosaic symptoms were collected randomly during 2019-2020 from Hangzhou (n=6) and Ningbo (n=4) in Zhejiang province and tested by RT-PCR with specific primer pairs to detect BBWV2, ASGV and CVB. RT-PCR and subsequent sequencing revealed that these three viruses were present in all the samples tested, indicating that co-infection of G. japonica by ASGV, CVB and BBWV2 is common. CVB mainly infects chrysanthemum (Singh et al. 2012), while ASGV is known as a pathogen of various fruit trees especially in the family Rosaceae, although there are recent reports that it can also infect some plants in Gramineae, Asparagaceae and Nelumbonaceae (Bhardwaj et al. 2017; Chen et al. 2019; He et al. 2019). Our results provide the first report that Gynura is a natural host of CVB and ASGV. Further surveys and biological studies are underway to evaluate the importance of Gynura as a virus reservoir for epidemics among the various hosts.

Construction of an infectious full-length cDNA clone of potato aucuba mosaic virus.

Potato aucuba mosaic virus (PAMV), a positive single-strand RNA virus, has one of the longest genomes of the viruses in the genus Potexvirus. In 2019, potato samples with mottle and crinkling symptoms from Huzhou, Zhejiang province, China, were identified to be infected with PAMV, potato virus X (PVX), and potato virus Y (PVY) by transcriptome sequencing. To study the effects of single infection by PAMV, the full-length sequence of PAMV from Huzhou (MT193476) was determined and an infectious full-length cDNA clone was constructed. This cDNA clone was infectious by agro-infiltration, leading to systemic symptoms in Nicotiana benthamiana, tomato, pepper, and potato.