Watermelon (Citrullus lanatus (Thunb.) Matsum. &Nakai) is an economic crop, which is widely cultivated around the world. The ploidy study of watermelon has an important role in field breeding and production, therefore, timely and convenient ploidy detection is necessary to accelerate its application. Traditionally, the ploidy of watermelon was determined by a series of time-consuming, expensive, and less efficient methods. In this study, we developed a more efficient method to simplify and accelerate the polyploidy identification in watermelons. We first confirmed the ploidy of watermelon by traditional tetraploid morphological features and well-established flow cytometry (FCM). Then we developed a reliable real-time quantitative PCR (qPCR) technique by quantifying the highly conserved 5S rDNA sequence and its copy numbers. This technique requires less sample collection and has comparable accuracy to FCM, it accelerates the analysis process and provides a new method for the identification of polyploidy of watermelon.

The ‘king of fruits’ mango (Mangifera indica) is widely cultivated in tropical areas and has been threatened by frequent extreme cold weather. Cyclic nucleotide–gated ion channel (CNGC) genes have an important function in the calcium-mediated development and cold response of plants. However, few CNGC-related studies are reported in mango, regardless of the mango cold stress response. In this study, we identified 43 CNGC genes in mango showing tissue-specific expression patterns. Five MiCNGCs display more than 3-fold gene expression induction in the fruit peel and leaf under cold stress. Among these, MiCNGC9 and MiCNGC13 are significantly upregulated below 6 °C, suggesting their candidate functions under cold stress. Furthermore, cell membrane integrity was damaged at 2 °C in the mango leaf, as shown by the content of malondialdehyde (MDA), and eight MiCNGCs are positively correlated with MDA contents. The high correlation between MiCNGCs and MDA implies MiCNGCs might regulate cell membrane integrity by regulating MDA content. Together, these findings provide a valuable guideline for the functional characterization of CNGC genes and will benefit future studies related to cold stress and calcium transport in mango.

Coffee is one of the most popular beverages around the world, which is mainly produced from the allopolyploid Coffea arabica. The genomes of C. arabica and its two ancestors C. canephora and C. eugenioides have been released due to the development of next generation sequencing. However, few studies on C. arabica are related to the PIN-FORMED (PIN) auxin efflux transporter despite its importance in auxin-mediated plant growth and development. In the present study, we conducted a genome-wide analysis of the PIN gene family in the three coffee species. Totals of 17, 9 and 10 of the PIN members were characterized in C. Arabica, C. canephora and C. eugenioides, respectively. Phylogenetic analysis revealed gene loss of PIN1 and PIN2 homologs in C. arabica, as well as gene duplication of PIN5 homologs during the fractionation process after tetraploidy. Furthermore, we conducted expression analysis of PIN genes in C. arabica by in silico and qRT-PCR. The results revealed the existence of gene expression dominance in allopolyploid coffee and illustrated several PIN candidates in regulating auxin transport and homeostasis under leaf rust fungus inoculation and the tissue-specific expression pattern of C. arabica. Together, this study provides the basis and guideline for future functional characterization of the PIN gene family.

Agave species are widely planted for fiber production. However, the molecular basis of agave fiber development has not been well understood. In this study, we performed a transcriptomic analysis in A. amaniensi, a well-known variety with high-quality fiber production. Approximately 43.87 million clean reads were obtained using Illumina sequencing. The de novo assembly produced 66,746 unigrams, 54% of which were annotated in a public database. In the Nr database, 21,490 unigenes of A. amaniensis were shown to be most closely related to Asparagus officinalis. Nine expansin A orthologs with full coding regions were obtained, which were named EXP1a, EXP1b, EXP2, EXP3, EXP4a, EXP4b, EXP11, EXP12, and EXP13. The maximum likelihood phylogenetic tree revealed the species-specific expansion of expansin genes in Arabidopsis, rice and agave. The expression analysis suggested the negative correlation between the expression of expansin genes and the leaf growth rate, except AhEXP11. Moreover, expansin genes were differentially affected by abiotic and biotic stresses. Notably, AhEXP2 expression level was highly upgraded after the infection of Phytophthora nicotiana. Nutrient deficiency also influent expansin genes expression. Together, our research will benefit future studies related to fiber development, disease resistance and nutrient usage in agave.

As one of the world’s most popular fruits, watermelon (Citrus lanatus) is cultivated in more than 3 million hectares across the globe, with a yearly yield of more than 100 million tons. According to ‘97103’ genome version 1, a previous study has shown that the watermelon genome consists of 11 PIN genes. However, the higher quality ‘97103’ genome version 2 was recently assembled by using PacBio long reads with the benefit of fast development sequencing technology. Using this new assembly, we conducted a new genome-wide search for PIN genes in watermelon and compared it with cucumber and melon genomes. We identified nine, nine, and eight PINs in watermelon, cucumber, and melon, respectively. Phylogenetic analysis revealed a distinct evolutionary history of PIN proteins in watermelon, which is shown by the orphan PIN6 in watermelon. We further conducted an expression analysis of the watermelon PIN genes in silico and by qRT-PCR. ClaPIN6 might not play an essential role during shoot regeneration, which is closely related to species-specific evolution. However, the up-regulated expression patterns of ClaPIN1-1 and ClaPIN1-3 indicated their important roles during shoot regeneration. The result of this research will benefit future studies to understand the regulating mechanisms of auxin in watermelon shoot regeneration.