Novel Insights into the Influence of Seed Sarcotesta Photosynthesis on Accumulation of Seed Dry Matter and Oil Content in Torreya grandis cv. "Merrillii"

The role and mechanism of TgCWIN2-mediated changes of photo-assimilates in modulating early development of Torreya grandis seeds

Early seed development is vital for plant reproduction, but the processes behind this in gymnosperms like Torreya grandis, which has a low rate of normal early-developed seeds, are not well understood. To fill this knowledge gap, we embarked on a comprehensive investigation encompassing the morphology and phenology of seed development in T. grandis. Using the 13C labelling analysis, coupled with leaf removal and seed thinning treatments, we observed a substantial increase in the content of photo-assimilate, an almost 10% increase in sucrose content under seed thinning treatments, thereby leading to an increase in the proportion of normal early-developed seeds, reaching 15%. Concurrently, through the integration of multi-omics analyses and transient overexpression validation, we identified cell wall invertase coding gene, TgCWIN2, which plays a pivotal role in sucrose cleavage during the early development of T. grandis seeds. Further gene co-expression, dual-luciferase assay, and yeast one-hybrid assay revealed that TgWRKY31 was a candidate regulator of TgCWIN2, positively influencing its expression by direct binding to the TgCWIN2 promoter. Notably, TgWRKY31 transient overexpression substantially enhances the expression of TgCWIN2, thereby contributing to a higher proportion of normal early-developed seeds. Our findings not only provide a comprehensive understanding of the underlying mechanisms governing the early development of T. grandis seeds, but are also essential for establishing strategies to enhance early seed development and improve yield.

Sucrose promotes cone enlargement via the TgNGA1-TgWRKY47-TgEXPA2 module in Torreya grandis

Cone enlargement is a crucial process for seed production and reproduction in gymnosperms. Most of our knowledge of cone development is derived from observing anatomical structure during gametophyte development. Therefore, the exact molecular mechanism underlying cone enlargement after fertilization is poorly understood. Here, we demonstrate that sucrose promotes cone enlargement in Torreya grandis, a gymnosperm species with relatively low rates of cone enlargement, via the TgNGA1-TgWRKY47-TgEXPA2 pathway. Cell expansion plays a significant role in cone enlargement in T. grandis. 13C labeling and sucrose feeding experiments indicated that sucrose-induced changes in cell size and number contribute to cone enlargement in this species. RNA-sequencing analysis, transient overexpression in T. grandis cones, and stable overexpression in tomato (Solanum lycopersicum) suggested that the expansin gene TgEXPA2 positively regulates cell expansion in T. grandis cones. The WRKY transcription factor TgWRKY47 directly enhances TgEXPA2 expression by binding to its promoter. Additionally, the NGATHA transcription factor TgNGA1 directly interacts with TgWRKY47. This interaction suppresses the DNA-binding ability of TgWRKY47, thereby reducing its transcriptional activation on TgEXPA2 without affecting the transactivation ability of TgWRKY47. Our findings establish a link between sucrose and cone enlargement in T. grandis and elucidate the potential underlying molecular mechanism.

Nutrient competition between female cones and young seeds in spring affects the physiological dropping and nut-setting rate in Torreya grandis

Physiological seed drop is a recognized phenomenon in economic forest, caused by the abscission of developing seeds due to intergroup competition for resources. However, little is known about the resource allocation dynamics in species exhibiting a biennial fruiting cycle, where interactions occur not only among seeds of the same year but also between reproductive structures from consecutive years. In this study, we explored the dynamics of resource allocation in Torreya grandis, a nut crop with a prototypical two-year seed development pattern. We implemented thinning treatments of 0%, 30%, and 60% on female cones and/or immature seeds during the spring, targeting various stages of development both pre- and post-pollination. Our findings reveal a pronounced resource competition in Torreya, evidenced by a natural seed-setting rate of merely 9.4%. Contrary to expectations, seed thinning did not lead to an obvious increase in nut-setting rates, whereas a substantial increase to 20.5% was observed when female cones were thinned by 60% at 20 days before pollination. The cone thinning treatment appears to have influenced seed development through positive cytokinin and negative abscisic acid effects. This indicates that intergroup competition between female cones and nuts is a more significant factor in seed drop than inner nut competition, and there seems to be an interaction between the two groups. We demonstrate that, in Torreya with biennial seed development, it is the competition between female cones and immature seeds that is important. This insight expands our comprehension of the physiological mechanisms governing seed drop in biennial fruiting species and managing the reproductive organ load to optimize nutrient allocation.

The relationship between canopy microclimate, fruit and seed yield, and quality in Xanthoceras sorbifolium

Xanthoceras sorbifolium has high oil content and important biomass energy value, but its development is limited by the problem of low yield. This study investigated the relationship between the canopy microclimate, fruit yield, and fruit quality of Xanthoceras sorbifolium. Difference between the distributions of canopy microclimate factors as well as fruit and seed parameters in the inner and outer canopies of the lower layer, as well as between the inner and outer canopies of the upper layer, were investigated for a period of one year. Canopy structure induced significant differences between canopy microclimate factors during various periods of the year. Light intensity and temperature of the outer and upper canopies were higher than those of inner and lower canopies. However, relative humidity showed an opposing trend. Light intensity was significantly and positively correlated with fruit set percentage, fruit yield, and seed yield. Temperature was significantly and positively correlated with fruit yield and seed yield, but significantly negatively correlated with the oil concentration of seed kernels. Fruit and seed yields significantly decreased from the outer to the inner canopy and from the upper to the lower canopy. Fruit set percentage in the outer canopy was also significantly higher than that in the inner canopy. However, oil concentrations in the seed kernels of the lower layer were significantly higher than those of the upper layer. Additionally, regression analysis was used to construct evaluation models for microclimate, fruit, and seed parameters. Regression equations corresponding to the association between single microclimatic factors during different periods and the fruit and seed parameters may provide a reference for canopy pruning and help develop an optimal regression model that may be used to predict and estimate fruit and seed parameters.

Contribution of the leaf and silique photosynthesis to the seeds yield and quality of oilseed rape (Brassica napus L.) in reproductive stage

Influences of photosynthesis of leaf and silique on seeds yield and quality of oilseed rape (Brassica napus L.) were explored in this study. A field comparing experiment with several rapeseed varieties was conducted and the results showed, that the leaf area index (LAI), silique surface area index (SAI), siliques number per plant, and biological yield were statistically classified as the first principal factors which greatly influenced seeds yield, the leaf net photosynthetic rate (P_n) and silique P_n were the second principal factors; the stomatal conductance (G_s) and chlorophyll a (Chl a) content were the first principal factors which influenced leaf P_n and silique P_n. A shading experiment was conducted and the results showed that, under treatments of the ZH1, ZH2, and ZH3 (shading rapeseed plants during flowering stage, during time from initial flowering until seeds ripening, and during time from flowering ending until seeds ripening, respectively), respectively the seeds yield per plant was reduced by 34.6%, 84.3%, and 86.1%, the seed protein content was significantly increased. The treatment ZH1 Not, but the ZH2 and ZH3 caused significant decrease in both seed oil content and oleic acid (C18:1) content in seed oil, and the contents of linoleic acid (C18:2), linolenic acid (C18:3) in oil were significantly increased, gene expression of the ACCase (Acetyl-CoA carboxylase), FAD2 (fatty acid desaturase), and FAD3 (ω-3 fatty acid dehydrogenase) in green seeds was restrained/changed. Thus the LAI, SAI, siliques number per plant, biological yield per plant, leaf P_n, silique P_n, and the G_s, Chl a content of leaf and silique formed an indexes system to be used in screening rapeseed variety with higher light efficiency and seeds yield; the silique photosynthesis inhibition and the photosynthates deficiency in rapeseed plant after flowering stage predominately influenced seeds yield and quality.

Effects of melatonin on growth and antioxidant capacity of naked oat (Avena nuda L) seedlings under lead stress

Melatonin (MT) plays an important role in plant response to abiotic stress. In recent years, lead (Pb) pollution has seriously affected the living environment of plants. In this study, we applied two different concentrations of MT to naked oat seedlings under Pb stress to explore the effect of MT on naked oat seedlings under Pb pollution. The results showed that Pb stress seriously inhibited the growth and development of naked oat seedlings, which was alleviated by MT. MT could increase the soluble protein content and decrease the proline content of naked oat seedlings to maintain the osmotic balance of naked oat seedlings. The application of MT could accelerate the removal of reactive oxygen species (ROS) and improve the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), so as to maintain the redox balance in naked oat seedlings. Exogenous melatonin could significantly increase the chlorophyll content of naked oat seedlings under Pb treatment, so as to improve the photosynthesis efficiency of naked oat seedlings. MT could also remarkably up regulate the expression of the genes of LOX, POX and Asmap1, and affect the expression of transcription factors NAC and WRKY1. It might regulate the expression of downstream genes through MAPKs pathways and TFs to improve the Pb tolerance of naked oat seedlings. These results proved that MT could significantly promote the growth and development of naked oats seedlings under Pb stress, which is expected to be applied in agricultural production practice.

Molecular and Photosynthetic Performance in the Yellow Leaf Mutant of Torreya grandis According to Transcriptome Sequencing, Chlorophyll a Fluorescence, and Modulated 820 nm Reflection

To study the photosynthetic energy mechanism and electron transfer in yellow leaves, transcriptomics combined with physiological approaches was used to explore the mechanism of the yellow leaf mutant Torreya grandis ‘Merrillii’. The results showed that chlorophyll content, the maximal photochemical efficiency of PSII (F_v/F_m), and the parameters related to the OJ phase of fluorescence (φ_Eo, φ_Ro) were all decreased significantly in mutant-type T. grandis leaves. The efficiency needed for an electron to be transferred from the reduced carriers between the two photosystems to the end acceptors of the PSI (δ_Ro) and the quantum yield of the energy dissipation (φ_Do) were higher in the leaves of mutant-type T. grandis compared to those in wild-type leaves. Analysis of the prompt fluorescence kinetics and modulated 820 nm reflection showed that the electron transfer of PSII was decreased, and PSI activity was increased in yellow T. grandis leaves. Transcriptome data showed that the unigenes involved in chlorophyll synthesis and the photosynthetic electron transport complex were downregulated in the leaves of mutant-type T. grandis compared to wild-type leaves, while there were no observable changes in carotenoid content and biosynthesis. These findings suggest that the downregulation of genes involved in chlorophyll synthesis leads to decreased chlorophyll content, resulting in both PSI activity and carotenoids having higher tolerance when acting as photo-protective mechanisms for coping with chlorophyll deficit and decrease in linear electron transport in PSII.

Acceleration of Aril Cracking by Ethylene in Torreya grandis During Nut Maturation

Torreya grandis 'Merrillii' is a famous nut with great nutritional value and high medicinal value. Aril cracking is an important process for seed dispersal, which is also an indicator of seed maturation. However, the cracking mechanism of T. grandis aril during the maturation stage remains largely unknown. Here, we provided a comprehensive view of the physiological and molecular levels of aril cracking in T. grandis by systematically analyzing its anatomical structure, physiological parameters, and transcriptomic response during the cracking process. These results showed that the length of both epidermal and parenchymatous cell layers significantly increased from 133 to 144 days after seed protrusion (DASP), followed by a clear separation between parenchymatous cell layers and kernel, which was accompanied by a breakage between epidermal and parenchymatous cell layers. Moreover, analyses of cell wall composition showed that a significant degradation of cellular wall polysaccharides occurred during aril cracking. To examine the global gene expression changes in arils during the cracking process, the transcriptomes (96 and 141 DASP) were analyzed. KEGG pathway analysis of DEGs revealed that 4 of the top 10 enriched pathways were involved in cell wall modification and 2 pathways were related to ethylene biosynthesis and ethylene signal transduction. Furthermore, combining the analysis results of co-expression networks between different transcription factors, cell wall modification genes, and exogenous ethylene treatments suggested that the ethylene signal transcription factors (ERF11 and ERF1A) were involved in aril cracking of T. grandis by regulation of EXP and PME. Our findings provided new insights into the aril cracking trait in T. grandis.

Photosynthetic Mechanisms of Metaxenia Responsible for Enlargement of Carya cathayensis Fruits at Late Growth Stages

Fruits of hickory (Carya cathayensis) are larger and their peel is greener after interspecific pollination by pecan (Carya illinoinensis; later pp fruits) than after intraspecific pollination by hickory (later ph fruits). Previous studies have found little genetic differences between offspring and their maternal parent, indicating that the observed trait differences between pp and ph fruits are due to metaxenia. Fruit development depends on the amount of photosynthetic assimilate available. Since there is no difference in photosynthesis of the associated leaves between pp and ph fruits, the larger size of the pp fruits might be attributed to changes in fruit photosynthesis caused by the different pollen sources. To elucidate to the photosynthetic mechanisms behind the metaxenia effect on fruit development in hickory, the effects of intraspecific and interspecific pollination regimes were examined in the present study. We observed the photosynthetic capacity in the peel of fruits and the related ecophysiological and morphological traits of both ph and pp fruits over a period of 120 days after pollination. Significant differences in the appearance and dry weight between ph and pp fruits were observed at 50 days after pollination (DAP). More than 70% of dry matter accumulation of the fruits was completed during 60-120 DAP, while the true photosynthetic rate of the associated leaves significantly decreased by about 50% during the same period. In several cell layers of the peel, the number of chloroplasts per cell was significantly higher in pp than in ph fruits. Similarly, the ribulose 1, 5-bisphosphate carboxylase (Rubisco) activity, the total chlorophyll content, and the nitrogen content were all significantly higher in pp than in ph fruits during all growth stages; and all of these physiological quantities were positively correlated with the gross photosynthetic rate of the fruits. We conclude that the enhanced photosynthetic capacity of pp fruits contributes to their fast dry matter accumulation and oil formation. This result will provide a theoretical basis for improving hickory fruit yields in practical cultivation.