Shade Avoidance 3 Mediates Crosstalk Between Shade and Nitrogen in Arabidopsis Leaf Development

After nitrogen treatments, plant leaves become narrower and thicker, and the chlorophyll content increases. However, the molecular mechanisms behind these regulations remain unknown. Here, we found that the changes in leaf width and thickness were largely compromised in the shade avoidance 3 (sav3) mutant. The SAV3 gene encodes an amino-transferase in the auxin biosynthesis pathway. Thus, the crosstalk between shade and nitrogen in Arabidopsis leaf development was investigated. Both hypocotyl elongation and leaf expansion promoted by the shade treatment were reduced by the high-N treatment; high-N-induced leaf narrowing and thickening were reduced by the shade treatment; and all of these developmental changes were largely compromised in the sav3 mutant. Shade treatment promoted SAV3 expression, while high-N treatment repressed SAV3 expression, which then increased or decreased auxin accumulation in cotyledons/leaves, respectively. SAV3 also regulates chlorophyll accumulation and nitrogen assimilation and thus may function as a master switch responsive to multiple environmental stimuli.

Functional Divergence of G and Its Homologous Genes for Green Pigmentation in Soybean Seeds

The degradation of chlorophyll in mature soybean seeds is closely related to the development of their yellow color. In this study, we examined G, its homologue G-like (GL), and their mutant alleles and investigated the relationship between these genes and chlorophyll accumulation in the seed coats of mature seeds. Transient expression of G and GL proteins fused with green fluorescent protein revealed that both were localized in plastids. Overexpression of G resulted in the accumulation of chlorophyll in the seed coats and cotyledons of mature seeds, indicating that high expression levels of G result in chlorophyll accumulation that exceeds its metabolism in the seeds of yellow soybean. Analysis of near isogenic lines at the G locus demonstrated a significant difference in the chlorophyll content of the seed coats and cotyledons of mature seeds when G and mutant g alleles were expressed in the d1d2 stay-green genetic background, indicating that the G protein might repress the SGR-independent degradation of chlorophyll. We examined the distribution of mutant alleles at the G and GL loci among cultivated and wild soybean germplasm. The g allele was widely distributed in cultivated soybean germplasm, except for green seed coat soybean lines, all of which contained the G allele. The gl alleles were much fewer in number than the g alleles and were mainly distributed in the genetic resources of cultivated soybean from Japan. None of the landraces and breeding lines investigated in this study were observed to contain both the g and gl alleles. Therefore, in conclusion, the mutation of the G locus alone is essential for establishing yellow soybeans, which are major current soybean breeding lines.

Transcriptome Analysis Reveals Genes Respond to Chlorophyll Deficiency in Green and Yellow Leaves of Chrysanthemum morifolium Ramat

Chlorophyll is vital for photosynthesis to produce sugars and other useful biochemical products in green plants. However, the molecular effects of chlorophyll deficiency in Chrysanthemum are largely unknown. In this study, we identified a bud sport mutant chrysanthemum belonging to the variety ‘Nannong Binyun’, which has yellow branches. Plant physiological studies have shown that the yellow color is revealed due to chlorophyll loss. RNA extracts of yellow and green tissues were analyzed using high-throughput RNA-sequencing, and a total of 11,649 tissue enriched unigenes that respond to chlorophyll deficiency were identified, including 4803 unigenes upregulated in yellow tissues and 6846 unigenes in green tissues. GO analysis revealed that these tissue-enriched genes may involve in the physiological processes of chlorophyll accumulation and photosynthesis. In addition, many DEGs from the families of AP2-EREBP, bHLH, MYB, and FAR1 that are associated with plant development and stress response were detected. Our study found that most of the genes from the GRAS family were downregulated in yellow leaves, indicating their putative roles in stem cell maintenance and possible contribution to leaf size determination.

Mechanism Underlying the Shading-Induced Chlorophyll Accumulation in Tea Leaves

Besides aroma and taste, the color of dry tea leaves, tea infusion, and infused tea leaves is also an important index for tea quality. Shading can significantly increase the chlorophyll content of tea leaves, leading to enhanced tea leaf coloration. However, the underlying regulatory mechanism remains unclear. In this study, we revealed that the expressions of chlorophyll synthesis genes were significantly induced by shading, specially, the gene encoding protochlorophyllide oxidoreductase (CsPOR). Indoor control experiment showed that decreased light intensity could significantly induce the expression of CsPOR, and thus cause the increase of chlorophyll content. Subsequently, we explored the light signaling pathway transcription factors regulating chlorophyll synthesis, including CsPIFs and CsHY5. Through expression level and subcellular localization analysis, we found that CsPIF3-2, CsPIF7-1, and CsHY5 may be candidate transcriptional regulators. Transcriptional activation experiments proved that CsHY5 inhibits CsPORL-2 transcription. In summary, we concluded that shading might promote the expression of CsPORL-2 by inhibiting the expression of CsHY5, leading to high accumulation of chlorophyll in tea leaves. The results of this study provide insights into the mechanism regulating the improvements to tea plant quality caused by shading.

Interdependent iron and phosphorus availability controls photosynthesis through retrograde signaling

Iron deficiency hampers photosynthesis and is associated with chlorosis. We recently showed that iron deficiency-induced chlorosis depends on phosphorus availability. How plants integrate these cues to control chlorophyll accumulation is unknown. Here, we show that iron limitation downregulates photosynthesis genes in a phosphorus-dependent manner. Using transcriptomics and genome-wide association analysis, we identify two genes, PHT4;4 encoding a chloroplastic ascorbate transporter and bZIP58, encoding a nuclear transcription factor, which prevent the downregulation of photosynthesis genes leading to the stay-green phenotype under iron-phosphorus deficiency. Joint limitation of these nutrients induces ascorbate accumulation by activating expression of an ascorbate biosynthesis gene, VTC4, which requires bZIP58. Furthermore, we demonstrate that chloroplastic ascorbate transport prevents the downregulation of photosynthesis genes under iron-phosphorus combined deficiency through modulation of ROS homeostasis. Our study uncovers a ROS-mediated chloroplastic retrograde signaling pathway to adapt photosynthesis to nutrient availability.

Cytosolic CTP Production Limits the Establishment of Photosynthesis in Arabidopsis

CTP synthases (CTPS) comprise a protein family of the five members CTPS1-CTPS5 in Arabidopsis, all located in the cytosol. Specifically, downregulation of CTPS2 by amiRNA technology results in plants with defects in chlorophyll accumulation and photosynthetic performance early in development. CTP and its deoxy form dCTP are present at low levels in developing seedlings. Thus, under conditions of fast proliferation, the synthesis of CTP (dCTP) can become a limiting factor for RNA and DNA synthesis. The higher sensitivity of ami-CTPS2 lines toward the DNA-Gyrase inhibitor ciprofloxacin, together with reduced plastid DNA copy number and 16S and 23S chloroplast ribosomal RNA support this view. High expression and proposed beneficial biochemical features render CTPS2 the most important isoform for early seedling development. In addition, CTPS2 was identified as an essential enzyme in embryo development before, as knock-out mutants were embryo lethal. In line with this, ami-CTPS2 lines also exhibited reduced seed numbers per plant.

Physiological characters of four lowland chilli varieties (Capsicum annum L.) with root cutting

The root system plays some vital roles in overall plant development, promoting plant anchorage, absorption of nutrients and water, and hormone production. Cutting is an attempt to root regeneration and enhance the plant's metabolism capability, including canopies and roots for high yielding. Non-hybrid chilli can be used as a model plant because Indonesia's chilli yield has not been maximal yet. This research was aimed to determine the physiological characters of four lowland chilli varieties with root cutting. This study was designed using a randomized, complete block design (RCBD) with two factors: root cutting and varieties. The root cutting factor consisted of 4 levels: root cutting in seeding, root cutting in ridging, root cutting in seedling and ridging, and non-cutting. The varieties factor consisted of 4 levels, namely Lembang, Kencana, Tanjung, dan Ungu. The results showed that root cutting in ridging for Kencana, Lembang, and Ungu increased stomatal conductance, transpiration rate, CO2 intercellular, chlorophyll accumulation, photosynthesis rate, and improved fruit yield per plant. However, Tanjung did not respond to root cutting treatment because it did not improve plant physiology characters and fruit yield than non-cutting treatment. It is concluded that root cutting in ridging can be improved plant physiology, which contributes to increasing yield on Kencana, Lembang, and Ungu.

Knockdown of NON-YELLOW COLORING 1 (NYC1)-like gene or chlorophyllin application enhanced chlorophyll accumulation with antioxidant roles in suppressing heat-induced leaf senescence in perennial ryegrass

Loss of chlorophyll (Chl) and oxidative damages co-occur during heat-induced leaf senescence. This study aimed to determine the functions of Chl catabolic gene, NON-YELLOW COLORING 1 (NYC1)-like (NOL) in regulating heat-induced leaf senescence and to characterize antioxidant roles of a Chl derivative, sodium copper chlorophyllin (SCC), in suppressing heat-induced leaf senescence. In two separate experiments, one by comparing NOL RNAi transgenic and wild-type plants, and the other by analyzing the effects of sodium copper chlorophyllin (SCC, 1 mM) treatment, perennial ryegrass (Lolium perenne) were exposed to heat stress (38/35 oC, day/night) or optimal temperature (25/20 oC). Results showed that both knockdown of LpNOL and application of SCC suppressed heat-induced leaf senescence, as manifested by increased Chl content, reduced electrolyte leakage, and down-regulation of Chl-catabolic genes and senescence-related genes, as well as enhanced antioxidant capacity in the peroxidase (POD) pathway for H2O2 scavenging. Ex vivo SCC incubation protected membranes from H2O2 damage onto mesophyll protoplasts of perennial ryegrass. The suppression of leaf senescence by knockdown of NOL or chlorophyllin application was associated with enhanced chlorophyll accumulation playing antioxidant roles in protecting leaves from heat-induced oxidative damages.

Phosphatidylglycerol synthesis facilitates plastid gene expression and light induction of nuclear photosynthetic genes

Phosphatidylglycerol (PG) is the only major phospholipid in the thylakoid membrane of chloroplasts. PG is essential for photosynthesis and loss of PG in Arabidopsis thaliana results in severe defects of growth and chloroplast development with decreased chlorophyll accumulation, impaired thylakoid formation, and downregulation of photosynthesis-associated genes encoded in nuclear and plastid genomes. However, how the absence of PG affects the gene expression and plant growth remains unclear. To elucidate this mechanism, we investigated the growth and transcriptional profiles of a PG-deficient Arabidopsis mutant pgp1-2 under various light conditions. Microarray analysis demonstrated that reactive oxygen species-responsive genes were upregulated in pgp1-2. Decreased growth light did not alleviated the impaired leaf development and the downregulation of photosynthesis-associated genes in pgp1-2, indicating limited impacts of photooxidative stress on the defects of pgp1-2. Illumination to dark-adapted pgp1-2 triggered downregulation of photosynthesis-associated nuclear-encoded genes (PhANGs), while plastid-encoded genes were constantly suppressed. Overexpression of GOLDEN2-LIKE1 (GLK1), a transcription factor regulating chloroplast development, in pgp1-2 upregulated PhANGs but not plastid-encoded genes along with chlorophyll accumulation. Our data suggest a broad impact of PG biosynthesis on nuclear-encoded genes partially via GLK1 and a specific involvement of this lipid in the plastid gene expression and plant development.

Comprehensive Analysis of the SBP Family in Blueberry and Their Regulatory Mechanism Controlling Chlorophyll Accumulation

SQUAMOSA Promoter Binding Protein (SBP) family genes act as central players to regulate plant growth and development with functional redundancy and specificity. Addressing the diversity of the SBP family in crops is of great significance to precisely utilize them to improve agronomic traits. Blueberry is an important economic berry crop. However, the SBP family has not been described in blueberry. In the present study, twenty VcSBP genes were identified through data mining against blueberry transcriptome databases. These VcSBPs could be clustered into eight groups, and the gene structures and motif compositions are divergent among the groups and similar within each group. The VcSBPs were differentially expressed in various tissues. Intriguingly, 10 VcSBPs were highly expressed at green fruit stages and dramatically decreased at the onset of fruit ripening, implying that they are important regulators during early fruit development. Computational analysis showed that 10 VcSBPs were targeted by miR156, and four of them were further verified by degradome sequencing. Moreover, their functional diversity was studied in Arabidopsis. Noticeably, three VcSBPs significantly increased chlorophyll accumulation, and qRT-PCR analysis indicated that VcSBP13a in Arabidopsis enhanced the expression of chlorophyll biosynthetic genes such as AtDVR, AtPORA, AtPORB, AtPORC, and AtCAO. Finally, the targets of VcSBPs were computationally identified in blueberry, and the Y1H assay showed that VcSBP13a could physically bind to the promoter region of the chlorophyll-associated gene VcLHCB1. Our findings provided an overall framework for individually understanding the characteristics and functions of the SBP family in blueberry.