Research on lncRNA Related to Drought Resistance of Shanlan Upland Rice

Background Drought has become the major abiotic stress that causes losses in rice yields and consequently is one of the main environmental factors threatening food security. Long non-coding RNA (lncRNA) is known to play an important role in plant response to drought stress, while the mechanisms of competing endogenous RNA (ceRNA) in drought resistance in upland rice have been rarely reported. Results In our study, a total of 191 lncRNAs, 2115 mRNAs and 32 miRNAs (microRNAs) were found by strand-specific sequencing and small RNA sequencing to be differentially expressed in drought-stressed rice. Functional analysis of results indicate that they play important roles in hormone signal transduction, chlorophyll synthesis, protein synthesis and other pathways. Construction of a ceRNA network revealed that MSTRG.28732.3 may interact with miR171 in the chlorophyll biosynthesis pathway and affect the ability of plants to withstand drought stress by regulating Os02g0662700, Os02g0663100 and Os06g0105350. The accuracy of the regulatory network was verified by qRT-PCR. Conclusion Our results provide a theoretical basis for future studies on the potential function of lncRNA in plant drought resistance, and they provide new genetic resources for drought-resistant rice breeding.

Phenylalanine Suppresses Cell Death Caused by Loss of Fumarylacetoacetate Hydrolase in Arabidopsis

Fumarylacetoacetate hydrolase (FAH) catalyzes the final step of Tyrosine (Tyr) degradation pathway essential to animals and the deficiency of FAH causes an inborn lethal disease. In plants, a role of this pathway was unknown until we found that mutation of Short-day Sensitive Cell Death1 (SSCD1), encoding Arabidopsis FAH, results in cell death under short day. Phenylalanine (Phe) could be converted to Tyr and then degraded in both animals and plants. Phe ingestion in animals worsens the disease caused by FAH defect. However, in this study we found that Phe represses cell death caused by FAH defect in plants. Phe treatment promoted chlorophyll biosynthesis and suppressed the up‑regulation of reactive oxygen species marker genes in the sscd1 mutant. Furthermore, the repression of sscd1 cell death by Phe could be reduced by α-aminooxi-β-phenylpropionic acid but increased by methyl jasmonate, which inhibits or activates Phe ammonia-lyase catalyzing the first step of phenylpropanoid pathway, respectively. In addition, we found that jasmonate signaling up‑regulates Phe ammonia-lyase 1 and mediates the methyl jasmonate enhanced repression of sscd1 cell death by Phe. These results uncovered the relation between chlorophyll biosynthesis, phenylpropanoid pathway and jasmonate signaling in regulating the cell death resulting from loss of FAH in plants.

Artificial Shading Can Adversely Affect Heat-tolerant Lettuce Growth and Taste, with Concomitant Changes in Gene Expression

Shading has been used to produce high-quality lettuce (Lactuca sativa) in locations where production conditions are not optimal for this cool-season crop. To learn what additional benefits shading provides if heat-tolerant cultivars are used and to understand the effects of shading on growth, sensory quality, chemical content, and transcriptome profile on heat-tolerant lettuce, we grew two romaine lettuce cultivars with and without shading using 50% black shadecloth in 2018 and 2019. Shading reduced plant leaf temperatures, lettuce head fresh weights, glucose and total sugars content, and sweetness, but not bitterness, whereas it increased lettuce chlorophyll b content compared with unshaded controls. Transcriptome analyses identified genes predominantly involved in chlorophyll biosynthesis, photosynthesis, and carbohydrate metabolism as upregulated in unshaded controls compared with shaded treatments. For the tested cultivars, which were bred to withstand high growing temperatures, it may be preferable to grow them under unshaded conditions to avoid increased infrastructure costs and obtain lettuce deemed sweeter than if shaded.

Effect of analcite on cadmium phytoavailability and phytotoxity

The interactive effects of Cd and natural siliceous mineral analcite on Cd phytotoxicity and rate of accumulation in plant tissues have been analyzed. The test-plants of corn and hemp were grown in pots under controlled conditions of light, temperature, and soil moisture for 21 days in experiments modeling the following treatments: (1) without any amendments (control); (2) with the application of 0.1 % and 0.5 % (by weight) of CdSO4; (3) Cd salts (CdSO4) + analcite 0.1 g, 0.25 g, and 0.5 g per container. Test-plants performance was assessed by their growth characteristics (shoot height and root length), the content of photosynthetic pigments, macro- and micronutrients in leaves. The effect of Cd on maize and hemp plants inhibited their growth, chlorophyll biosynthesis in the leaves, led to a change in the balance of macro- and microelements, which leads to the accumulation of Cd in the tissues of shoots of both studied crops. Application of analcite partially compensated for the negative effects of Cd salts on the crop’s growth, chlorophyll content, and balance of nutrients and reduced Cd accumulation significantly in shoots.

A Foliar Pigment-Based Bioassay for Interrogating Chloroplast Signalling Reveals that Chlorophyll Biosynthesis Requires Carotenoid Isomerisation.

Background: Plastid-derived metabolites can signal control over nuclear gene expression, chloroplast biogenesis, and chlorophyll biosynthesis. Norflurazon (NFZ) inhibition of carotenoid biosynthesis in seedlings can elicit a protoporphyrin retrograde signal that controls chlorophyll and chloroplast biogenesis. Recent evidence reveals that plastid development can be regulated by carotenoid cleavage products called apocarotenoids. The key steps in carotenoid biosynthesis and catabolism that generate apocarotenoid signalling metabolites in foliar tissues remains to be elucidated. Here, we established an Arabidopsis foliar pigment-based bioassay using detached rosettes to differentiate plastid signalling processes in young expanding leaves containing dividing cells with active chloroplast biogenesis, from fully expanded leaves containing mature chloroplasts. Results: We demonstrate that environmental (extended darkness and cold exposure) as well as chemical (norflurazon; NFZ) inhibition of carotenoid biosynthesis can reduce chlorophyll levels in young, but not older leaves following a 24 h of rosette treatment. Mutants that disrupted xanthophyll accumulation, phytohormone biosynthesis (abscisic acid and strigolactone), or enzymatic carotenoid cleavage, did not alter chlorophyll levels in young or old leaves. Perturbations in acyclic cis-carotene biosynthesis revealed that disruption of CAROTENOID ISOMERASE (CRTISO), but not ZETA-CAROTENE ISOMERASE (Z-ISO) activity, reduced chlorophyll levels in young but not older leaves of plants growing under a long photoperiod. NFZ-induced inhibition of PHYTOENE DESATURASE (PDS) activity triggered phytoene accumulation more so in younger relative to older leaves from both WT and the crtiso mutant, indicating a continued substrate supply from the methylerythritol 4-phosphate (MEP) pathway for carotenogenesis. NFZ treatment of WT and crtiso mutant rosettes reveal similar, additive, and opposite effects on individual pigment accumulation.Conclusion: The Arabidopsis foliar pigment-based bioassay was used to differentiate signalling events elicited by environmental, chemical, genetic, and combinations thereof, that control chlorophyll biosynthesis. Genetic perturbations that impaired xanthophyll biosynthesis and/or carotenoid catabolism did not affect chlorophyll biosynthesis. The lack of CAROTENOID ISOMERISATION generated a signal that rate-limited chlorophyll accumulation, but not phytoene biosynthesis in young Arabidopsis leaves exposed to a long photoperiod. Findings generated using this new foliar pigment bioassay implicate that carotenoid isomerisation and NFZ elicit different signalling pathways to control chlorophyll homeostasis in young emerging leaves.

Identification and Characterization of an Early Leaf Senescence Gene ELS1 in Soybean

Early leaf senescence phenotype in soybean could be helpful to shorten the maturation period and prevent green stem disorder. From a high-density mutation library, we identified two early leaf senescence soybean mutant lines, els1-1 (early leaf senescence 1) and els1-2. The chlorophyll contents of both els1-1 and els1-2 were low in pre-senescent leaves. They degraded rapidly in senescent leaves, revealing that ELS1 is involved in chlorophyll biosynthesis during leaf development and chlorophyll degradation during leaf senescence. The causal mutations in els1 were identified by next-generation sequencing-based bulked segregant analysis. ELS1 encodes the ortholog of the Arabidopsis CaaX-like protease BCM1, which is localized in chloroplasts. Soybean ELS1 was highly expressed in green tissue, especially in mature leaves. The accumulation of photosystem I core proteins and light-harvesting proteins in els1 was low even in pre-senescent leaves, and their degradation was accelerated during leaf senescence. These results suggest that soybean ELS1 is involved in both chlorophyll synthesis and degradation, consistent with the findings in Arabidopsis BCM1. The gene els1, characterized by early leaf senescence and subsequent early maturation, does not affect the flowering time. Hence, the early leaf senescence trait regulated by els1 helps shorten the harvesting period because of early maturation characteristics. The els1-1 allele with weakly impaired function of ELS1 has only a small effect on agricultural traits and could contribute to practical breeding.

Important Roles of Key Genes and Transcription Factors in Flower Color Differences of Nicotiana alata

Nicotiana alata is an ornamental horticultural plant with a variety of flower colors and a long flowering period. The genes in four different colored N. alata (white, purple, red, and lemon green) were analyzed to explain the differences in flower color using transcriptomes. A total of 32 differential expression genes in the chlorophyll biosynthesis pathway and 41 in the anthocyanin biosynthesis pathway were identified. The enrichment analysis showed that the chlorophyll biosynthesis pathway and anthocyanin biosynthesis pathway play critical roles in the color differences of N. alata. The HEMA of the chlorophyll biosynthesis pathway was up-regulated in lemon green flowers. Compared with white flowers, in the red and purple flowers, F3H, F3′5′H and DFR were significantly up-regulated, while FLS was significantly down-regulated. Seventeen differential expression genes homologous to transcription factor coding genes were obtained, and the homologues of HY5, MYB12, AN1 and AN4 were also involved in flower color differences. The discovery of these candidate genes related to flower color differences is significant for further research on the flower colors formation mechanism and color improvements of N. alata.

SlZHD17 is involved in the control of chlorophyll and carotenoid metabolism in tomato fruit

Chlorophylls and carotenoids are essential and beneficial substances for both plant and human health. Identifying the regulatory network of these pigments is necessary for improving fruit quality. In a previous study, we identified an R2R3-MYB transcription factor, SlMYB72, that plays an important role in chlorophyll and carotenoid metabolism in tomato fruit. Here, we demonstrated that the SlMYB72-interacting protein SlZHD17, which belongs to the zinc-finger homeodomain transcription factor family, also functions in chlorophyll and carotenoid metabolism. Silencing SlZHD17 in tomato improved multiple beneficial agronomic traits, including dwarfism, accelerated flowering, and earlier fruit harvest. More importantly, downregulating SlZHD17 in fruits resulted in larger chloroplasts and a higher chlorophyll content. Dual-luciferase, yeast one-hybrid and electrophoretic mobility shift assays clarified that SlZHD17 regulates the chlorophyll biosynthesis gene SlPOR-B and chloroplast developmental regulator SlTKN2 in a direct manner. Chlorophyll degradation and plastid transformation were also retarded after suppression of SlZHD17 in fruits, which was caused by the inhibition of SlSGR1, a crucial factor in chlorophyll degradation. On the other hand, the expression of the carotenoid biosynthesis genes SlPSY1 and SlZISO was also suppressed and directly regulated by SlZHD17, which induced uneven pigmentation and decreased the lycopene content in fruits with SlZHD17 suppression at the ripe stage. Furthermore, the protein–protein interactions between SlZHD17 and other pigment regulators, including SlARF4, SlBEL11, and SlTAGL1, were also presented. This study provides new insight into the complex pigment regulatory network and provides new options for breeding strategies aiming to improve fruit quality.