Maize yellow mosaic virus (MaYMV) hosted in various gramineous plants was assigned to the genus Polerovirus (family Luteoviridae) in 2018. However, little is known about its genetic diversity and population structure. In this study, 509 sugarcane leaf samples with mosaic symptoms were collected in 2017 to 2019 from eight sugarcane-growing provinces in China. Reverse-transcription PCR results revealed that four positive-sense RNA viruses were found to infect sugarcane, and the incidence of MaYMV among samples from Fujian, Sichuan, and Guangxi Provinces was 52.1, 9.8, and 2.5%, respectively. Based on 82 partial MaYMV sequences and 46 whole-genome sequences from different host plants, phylogenetic analysis revealed that MaYMV populations are very closely associated with their source geographical regions (China, Africa, and South America). Pairwise identity analysis showed significant variability in genome sequences among MaYMV isolates with genomic nucleotide identities of 91.1 to 99.9%. In addition to codon mutations, insertions or deletions also contributed to genetic variability in individual coding regions, especially in the readthrough protein (P3-P5 fusion protein). Low gene flow and significant genetic differentiation of MaYMV were observed among the three geographical populations, suggesting that environmental adaptation is an important evolutionary force that shapes the genetic structure of MaYMV. Genes in the MaYMV genome were subject to strong negative or purification selection during evolution, except for the movement protein (MP), which was under positive selection pressure. This finding suggests that the MP may play an important role in MaYMV evolution. Taken together, our findings provide basic information for the development of an integrated disease management strategy against MaYMV.

Mosaic diseases of sugarcane caused by various viruses have been reported in most sugarcane planting countries and threaten global sugar production. There is a lack of extensive, systematic investigation of mosaic diseases and their causal viruses in China. In this study, a total of 901 leaf samples showing mosaic symptoms were collected from commercial fields in eight provincial regions in China and tested for sorghum mosaic virus (SrMV), sugarcane mosaic virus (SCMV), sugarcane streak mosaic virus (SCSMV), and maize yellow mosaic virus (MaYMV) using RT-PCR with four specific primer pairs. Of 901 tested samples, 38.5% (347/901) of samples were infected with one of the four viruses alone. Infection by two or more viruses was seen for 42.6% (384/901) of samples. The highest incidence of virus-causing sugarcane mosaic disease was SrMV (70.1%), followed by SCMV (33.4%) and SCSMV (30.3%), and the lowest incidence was seen for MaYMV (5.1%). Three viruses (SrMV, SCMV, and SCSMV) were found in eight sugarcane-planting provinces, whereas MaYMV was only found in Fujian, Guangxi, and Sichuan provinces. Mixed infections of the three main viruses, particularly for SrMV + SCMV and SrMV + SCSMV, were commonly found in the sugarcane samples. Our systematic determination of the occurrence and distribution of four RNA viruses associated with sugarcane mosaic diseases can provide evidence to guide the development of strategies for the prevention and control of sugarcane mosaic diseases in China.

Heat stress is an increasingly significant abiotic stress factor affecting crop yield and quality. This study aims to uncover the regulatory mechanism of sweet corn response to heat stress by integrating transcriptome and metabolome analyses of seedlings exposed to normal (25 °C) or high temperature (42 °C). The transcriptome results revealed numerous pathways affected by heat stress, especially those related to phenylpropanoid processes and photosynthesis, with 102 and 107 differentially expressed genes (DEGs) identified, respectively, and mostly down-regulated in expression. The metabolome results showed that 12 or 24 h of heat stress significantly affected the abundance of metabolites, with 61 metabolites detected after 12 h and 111 after 24 h, of which 42 metabolites were detected at both time points, including various alkaloids and flavonoids. Scopoletin-7-o-glucoside (scopolin), 3-indolepropionic acid, acetryptine, 5,7-dihydroxy-3′,4′,5′-trimethoxyflavone, and 5,6,7,4′-tetramethoxyflavanone expression levels were mostly up-regulated. A regulatory network was built by analyzing the correlations between gene modules and metabolites, and four hub genes in sweet corn seedlings under heat stress were identified: RNA-dependent RNA polymerase 2 (RDR2), UDP-glucosyltransferase 73C5 (UGT73C5), LOC103633555, and CTC-interacting domain 7 (CID7). These results provide a foundation for improving sweet corn development through biological intervention or genome-level modulation.

Upon pathogen attack, cytosolic Ca²⁺ levels increase in plant cells. The first innate immune response is activated by detecting microbe/pathogen-associated molecular patterns (MAMPs/PAMPs) and is called PAMPs-triggered immunity (PTI). The second immune response is triggered by recognizing pathogens' effector proteins named effectors-triggered immunity (ETI). Calcium-dependent protein kinases (CDPKs or CPKs) are well-known calcium sensors that have a mediator role both in PTI and ETI. Calcium can bind to the elongation factor (EF)-hand domain at the C-terminus of CDPKs, which then phosphorylates substrates at the N-terminal catalytic kinase domain to transfer calcium signals directly. Improving the stress resilience of crops is a critical strategy in attaining global food security. In plants, when a stimulus is seen, there is an increase in Ca²⁺ concentration, which activates CDPKs which are in charge of sending out the immunological signals needed for disease tolerance. During the immune response, CDPKs are subject to numerous levels of regulation, including Ca²⁺ dependency to decipher various Ca²⁺ signals. Furthermore, salicylic acid (SA) regulation by CDPKs provides a comprehensive overview of CDPKs-mediated SA signaling during immune response in plants under pathogen attack. The critical part of CDPKs in SA biosynthesis, from the regulation of SA biosynthesis to how NPR1 perceives SA upon biotic stress, is comprehensively reviewed in this paper with the latest advancements in research. However, more research about CDPKs-mediated SA signaling under pathogen attack is mandatory to further dissect their co-role in crop protection against various diseases to achieve sustainable production goals in the future.

Mutation of the MATRILINEAL gene in sugarcane induces in vivo maternal haploids and suggests prospects for sugarcane breeding.

The novel virus, Maize yellow mosaic virus (MaYMV, genus Polerovirus of family Luteoviridae), was first reported to infect maize (Zea mays L.) in Yunnan, Guizhou, and Anhui provinces, China in 2016 (Chen et al. 2016; Wang et al. 2016). Since then, this virus was found to infect diverse plants in the family Poaceae, including maize (Gonçalves et al., 2017), itch grass (Yahaya et al. 2017), Panicum miliaceum, and Sorghum bicolor (Lim et al. 2017) from other countries in Asia, Africa, and South America. However, MaYMV has only been reported infecting sugarcane in Nigeria (Yahaya et al. 2017), with no reports from Asia. Here, we collected leaf tissue samples with yellowish stripes and yellow mosaic symptoms in Saccharum spp. hybrid plants from fields located in Fuzhou (Fujian province) and Neijiang (Sichuan province), China in 2018 (Fig. 1-A and -B). In addition, symptomatic leaf tissue was sampled from maize in Neijiang, Sichuan province (Fig. 1-C). All symptomatic leaf samples (sugarcane = 13; maize = 1) we...