C2H2-type zinc finger proteins (C2H2-ZFPs) play a key role in various plant biological processes and responses to environmental stresses. In Arabidopsisthaliana, C2H2-ZFP members with two zinc finger domains have been well-characterized in response to abiotic stresses. To date, the functions of these genes in strawberries are still uncharacterized. Here, 126 C2H2-ZFPs in cultivated strawberry were firstly identified using the recently sequenced Fragaria × ananassa genome. Among these C2H2-ZFPs, 46 members containing two zinc finger domains in cultivated strawberry were further identified as the C1-2i subclass. These genes were unevenly distributed on 21 chromosomes and classified into five groups according to the phylogenetic relationship, with similar physicochemical properties and motif compositions in the same group. Analyses of conserved domains and gene structures indicated the evolutionary conservation of the C1-2i subclass. A Ka/Ks analysis indicated that the C1-2i members were subjected to purifying selection during evolution. Furthermore, FaZAT10, a typical C2H2-ZFP, was isolated. FaZAT10 was expressed the highest in roots, and it was induced by drought, salt, low-temperature, ABA, and MeJA treatments. It was localized in the nucleus and showed no transactivation activity in yeast cells. Overall, these results provide useful information for enriching the analysis of the ZFPs gene family in strawberry, and they provide support for revealing the mechanism of FaZAT10 in the regulatory network of abiotic stress.

Huanglongbing (HLB) is an obstinate disease in the citrus industry. No resistant citrus resources were currently available, but various degrees of Huanglongbing tolerance exist in different germplasm. Citrus junos is emerging as one of the popular rootstocks widely used in the citrus production. However, its responses to the HLB causal agent, Candidatus Liberibacter asiaticus (CLas), were still elusive. In the current study, we investigated the physiological, anatomical, and metabolomic responses of a C. junos rootstock ‘Pujiang Xiangcheng’ by a controlled CLas grafting inoculation. The summer flushes and roots were impaired at 15 weeks after inoculation, although typical leaf symptomatic phenotypes were not obvious. The chlorophyll pigments and the photosynthetic rate were compromised. The phloem sieve tubes were still working, despite the fact that the callose was deposited and the starch granules were accumulated in the phloem cells. A wide, targeted metabolomic analysis was carried out to explore the systematic alterations of the metabolites at this early stage of infection in the leaves and root system. The differentially accumulated metabolites in the CLas-affected leaves and roots compared with the mock-inoculation control tissues revealed that distinct responses were obvious. Besides the commonly observed alteration of sugar and amino acids, the active break down of starch in the roots was discovered. The different types of fatty acids were altered in the two tissues, with a more pronounced content decline in the roots. Our results not only provided fundamental knowledge about the response of the C. junos rootstock to the HLB disease, but also presented new insights into the host–pathogen interaction in the early stages.

The use of alternative transcription start or termination sites (aTSS or aTTS) as well as alternative splicing (AS) produce diverse transcript isoforms, playing indispensable roles in the plant development and environmental adaptations. Despite the advances in the finding of the genome-wide alternatively spliced genes in strawberry, it remains unexplored how AS responds to the developmental cues and what relevance do these outcomes have to the gene function. In this study, we have systematically investigated the transcriptome complexity using long-read Oxford Nanopore Technologies along the four successive developmental stages. The full-length cDNA sequencing results unraveled thousands of previously unexplored transcript isoforms raised from aTSS, aTTS, and AS. The relative contributions of these three processes to the complexity of strawberry fruit transcripts were compared. The aTSS and aTTS were more abundant than the AS. Differentially expressed transcripts unraveled the key transitional role of the white fruit stage. Isoform switches of transcripts from 757 genes were observed. They were associated with protein-coding potential change and domain gain or loss as the main consequences. Those genes with switched isoforms take part in the key processes of maturation in the late stages. A case study using yeast two hybrid analysis supported the functional divergence of the two isoforms of the B-box protein 22. Our results provided a new comprehensive overview of the dynamic transcriptomic landscape during strawberry fruit development and maturation.

Hexokinase1 (HXK1) is a bifunctional enzyme that plays indispensable roles in plant growth, nitrogen utilization, and stress resistance. However, information on the HXK family members of strawberries and their functions in glucose sensing and metabolic regulation is scarce. In the present study, four HXKs were firstly identified in the genome of Fragaria vesca and F. pentaphylla. The conserved domains of the HXK1s were confirmed, and a site-directed mutation (S177A) was introduced into the FpHXK1. FpHXK1, which shares the highest identity with the AtHXK1 was able to restore the glucose sensitivity and developmental defects of the Arabidopsis gin2-1 mutant, but not its kinase-activity-impaired mutant (FpHXK1S177A). The transcription of FpHXK1 was dramatically up-regulated under PEG-simulated drought stress conditions. The inhibition of the HXK kinase activity delayed the strawberry plant’s responses to drought stress. Transient overexpression of the FpHXK1 and its kinase-impaired mutant differentially affected the level of glucose, sucrose, anthocyanins, and total phenols in strawberry fruits. All these results indicated that the FpHXK1, acting as a glucose sensor, was involved in drought stress response and sugar metabolism depending on its kinase activity.