Comprehensive Analysis of BrHMPs Reveals Potential Roles in Abiotic Stress Tolerance and Pollen-Stigma Interaction in Brassica rapa.

Heavy metal-associated proteins (HMPs) participate in heavy metal detoxification. Although HMPs have been identified in several plants, no studies to date have identified the HMPs in Brassica rapa (B. rapa). Here, we identified 85 potential HMPs in B. rapa by bioinformatic methods. The promoters of the identified genes contain many elements associated with stress responses, including response to abscisic acid, low-temperature, and methyl jasmonate. The expression levels of BrHMP14, BrHMP16, BrHMP32, BrHMP41, and BrHMP42 were upregulated under Cu2+, Cd2+, Zn2+, and Pb2+ stresses. BrHMP06, BrHMP30, and BrHMP41 were also significantly upregulated after drought treatment. The transcripts of BrHMP06 and BrHMP11 increased mostly under cold stress. After applying salt stress, the expression of BrHMP02, BrHMP16, and BrHMP78 was induced. We observed increased BrHMP36 expression during the self-incompatibility (SI) response and decreased expression in the compatible pollination (CP) response during pollen-stigma interactions. These changes in expression suggest functions for these genes in HMPs include participating in heavy metal transport, detoxification, and response to abiotic stresses, with the potential for functions in sexual reproduction. We found potential co-functional partners of these key players by protein-protein interaction (PPI) analysis and found that some of the predicted protein partners are known to be involved in corresponding stress responses. Finally, phosphorylation investigation revealed many phosphorylation sites in BrHMPs, suggesting post-translational modification may occur during the BrHMP-mediated stress response. This comprehensive analysis provides important clues for the study of the molecular mechanisms of BrHMP genes in B. rapa, especially for abiotic stress and pollen-stigma interactions.

Stigma receptors control intraspecies and interspecies barriers in Brassicaceae.

Flowering plants have evolved numerous intraspecific and interspecific prezygotic reproductive barriers to prevent production of unfavourable offspring1. Within a species, self-incompatibility (SI) is a widely utilized mechanism that rejects self-pollen2,3 to avoid inbreeding depression. Interspecific barriers restrain breeding between species and often follow the SI × self-compatible (SC) rule, that is, interspecific pollen is unilaterally incompatible (UI) on SI pistils but unilaterally compatible (UC) on SC pistils1,4-6. The molecular mechanisms underlying SI, UI, SC and UC and their interconnections in the Brassicaceae remain unclear. Here we demonstrate that the SI pollen determinant S-locus cysteine-rich protein/S-locus protein 11 (SCR/SP11)2,3 or a signal from UI pollen binds to the SI female determinant S-locus receptor kinase (SRK)2,3, recruits FERONIA (FER)7-9 and activates FER-mediated reactive oxygen species production in SI stigmas10,11 to reject incompatible pollen. For compatible responses, diverged pollen coat protein B-class12-14 from SC and UC pollen differentially trigger nitric oxide, nitrosate FER to suppress reactive oxygen species in SC stigmas to facilitate pollen growth in an intraspecies-preferential manner, maintaining species integrity. Our results show that SRK and FER integrate mechanisms underlying intraspecific and interspecific barriers and offer paths to achieve distant breeding in Brassicaceae crops.

Effects of soil waterlogging and high-temperature stress on photosynthesis and photosystem II of ginger (Zingiber officinale).

Heavy waterlogging and high temperatures occur frequently in North China, yet the effects of changing environments on photochemical reactions and carbon metabolism have not been described in ginger. To determine the impact of waterlogging and high temperature on ginger, in this study, treatment groups were established as follows: (a) well-watered at ambient temperature (28 °C/22 °C) (CK), (b) well-watered at moderate temperature (33 °C/27 °C) (MT), (c) well-watered at high temperature (38 °C/32 °C) (HT), (d) waterlogging at ambient temperature (CK-WL), (e) waterlogging at moderate temperature (MT-WL), and (f) waterlogging at high temperature (HT-WL) during the rhizome growth period. We analyzed the effect of different treatments on the photosynthetic performance of ginger. Here, our results showed that waterlogging and high temperature irreversibly decreased the photosynthetic pigment content, increased the ROS content of leaves, inhibited leaf carbon assimilation and limited PSII electron transport efficiency. In addition, waterlogging in isolation and high temperature in isolation affected photosynthesis to varying degrees. Taken together, photosynthesis was more sensitive to the combined stress than to the single stresses. The results of this research provide deep insights into the response mechanisms of crop photosynthesis to different water and temperature conditions and aid the development of scientific methods for mitigating plant damage over time.

Endophytic extract Zhinengcong alleviates heat stress-induced reproductive defect in Solanum lycopersicum.

High temperature negatively affects reproductive process significantly, leading to tremendous losses in crop quality and yield. Zhinengcong (ZNC), a crude extract from the endophytic fungus Paecilomyces variotii, has been shown to improve plant growth and resistance to biotic and abiotic stresses. We show here that ZNC can also alleviate heat stress-induced reproductive defects in Solanum lycopersicum, such as short-term heat-induced inhibition on pollen viability, germination and tube growth, and long-term heat stress-induced pollen developmental defects. We further demonstrated that ZNC alleviates heat stress by downregulating the expressions of ROS production-related genes, RBOHs, and upregulating antioxidant related genes and the activities of the corresponding enzymes, thus preventing the over accumulation of heat-induced reactive oxygen species (ROS) in anther, pollen grain and pollen tube. Furthermore, spraying application of ZNC onto tomato plants under long-term heat stress promotes fruit and seed bearing in the field. In summary, plant endophytic fungus extract ZNC promotes the reproductive process and yield of tomato plants under heat stress and presents excellent potential in agricultural applications.