Fruit cracking has long been a topic of great concern for growers and researchers of litchi (Litchi chinensis Sonn.). To understand the molecular mechanisms underlying fruit cracking, high-throughput RNA sequencing (RNA-Seq) was first used for de novo assembly and characterization of the transcriptome of cracking pericarp of litchi. Comparative transcriptomic analyses were performed on non-cracking and cracking fruits. A total of approximately 26 million and 29 million high quality reads were obtained from the two groups of samples, and were assembled into 46,641 unigenes with an average length of 993 bp. These unigenes can be useful resources for future molecular studies of the pericarp in litchi. Furthermore, four genes (LcAQP, 1; LcPIP, 1; LcNIP, 1; LcSIP, 1) involved in water transport, five genes (LcKS, 2; LcGA2ox, 2; LcGID1, 1) involved in GA metabolism, 21 genes (LcCYP707A, 2; LcGT, 9; Lcβ-Glu, 6; LcPP2C, 2; LcABI1, 1; LcABI5, 1) involved in ABA metabolism, 13 genes (LcTPC, 1; Ca²⁺/H⁺ exchanger, 3; Ca²⁺-ATPase, 4; LcCDPK, 2; LcCBL, 3) involved in Ca transport and 24 genes (LcPG, 5; LcEG, 1; LcPE, 3; LcEXP, 5; Lcβ-Gal, 9; LcXET, 1) involved in cell wall metabolism were identified as genes that are differentially expressed in cracked fruits compared to non-cracked fruits. Our results open new doors to further understand the molecular mechanisms behind fruit cracking in litchi and other fruits, especially Sapindaceae plants.

Mango flowering is highly sensitive to temperature changes. In this research, the maximum values of pollen germination rate (PGR), pollen tube length (PTL) and their cardinal temperatures (Tmin, Topt and Tmax) were estimated by using quadratic equation and modified bilinear model under the conditions of 14–36 °C. The pollen germination rate in four mango varieties ranged from 29.1% (‘Apple mango’) to 35.5% (‘Renong No. 1’); the length of pollen tube ranged from 51.2 μm (‘Deshehari’) to 56.6 μm (‘Jinhuang’). The cardinal temperatures ranges (Tmin, Topt and Tmax) of pollen germination were 20.3–22.8 °C, 26.7–30.6 °C and 30.4–34.3 °C, respectively; similarly, cardinal temperatures (Tmin, Topt and Tmax) of pollen tube growth were 20.3–21.2 °C, 27.9–32.1 °C and 30.2–34.4 °C respectively. Of those, ‘Renong No. 1’ could maintain relatively high pollen germination rate even at 30 °C, however, ‘Deshehari’ had the narrowest adaptive temperature range. These results were further confirmed by changes of superoxide dismutase, catalase activity and malondialdehyde content. These results showed that mango flowering was highly sensitive to temperature changes and there were significant differences in pollen germination rate and pollen tube length among different varieties. Current research results were of great significance for the introduction of new mango varieties in different ecological regions, the cultivation and management of mango at the flowering stage and the breeding of new mango varieties.

Chromium (Cr) is one of the most toxic heavy metals in the environment. The tolerance to metal stress involves sophisticated regulation of gene expression networks, which involve microRNAs (miRNAs). However, the role of miRNAs in Cr stress response in Avicennia marina has not been resolved, and was addressed here. The analysis of response characteristics revealed that morpho-physiological traits such as root length, Cr accumulation level and antioxidant enzyme activity all exhibit significant changes under Cr stress. Via sRNA sequencing, a total of 27 known and 149 novel miRNAs were identified, 63 of which showed differential expression after Cr stress (q-value < 0.001). Further, 571 miRNA-target interaction pairs were identified for differentially expressed miRNAs, corresponding to 355 target genes. GO and KEGG analyses indicated that these target genes could participate in stress-related biological processes such as signal transduction, transcription regulation, protein synthesis and the MAPK signaling pathway. 54 miRNA target genes, corresponding to 37 miRNAs such as Ama-miR160, Ama-nmiR25-5p and Ama-nmiR118-5p, were enriched for “plant signal hormone transduction” (ko04075), “phenylpropanoid biosynthesis” (ko00940) and “MAPK signaling pathway” (ko04016), which indicated an important role of these miRNAs in regulating Cr stress response in A. marina. Based on the findings, a Cr stress-responsive regulatory model was developed, offering new insights into the molecular regulatory mechanisms of Cr response. In conclusion, this study shows the identity and potential role of miRNAs in the heavy metal stress response of A. marina, and provides the foundation for future research.