Wheat Leaf Development Research Articles

The TaWAK2-TaNAL1-TaDST pathway regulates leaf width via cytokinin signaling in wheat.

Leaves play a crucial role in photosynthesis and respiration, ultimately affecting the final grain yield of crops, including wheat (Triticum aestivum L.); however, the molecular mechanisms underlying wheat leaf development remain largely unknown. Here, we isolated a narrow-leaf gene, TaWAK2-A, through a map-based cloning strategy. TaWAK2-A encodes a wall-associated kinase (WAK), for which a single Ala-to-Val amino acid substitution reduces the protein stability, leading to a narrow-leaf phenotype in wheat. Further investigation suggests that TaWAK2 directly interacts with and phosphorylates TaNAL1, a trypsin-like serine/cysteine protease. The phosphorylated TaNAL1 is then involved in the degradation of the zinc finger transcription factor TaDST, which acts as a repressor of leaf expansion by activating the expression of the cytokinin oxidase gene TaCKX9 and triggering in vivo cytokinin degradation. Therefore, our findings elucidate a signaling cascade involving TaWAK2-TaNAL1-TaDST that sheds light on the regulation of wheat leaf development.

Characterization and Mapping of a Rolling Leaf Mutant Allele rlT73 on Chromosome 1BL of Wheat.

Leaf rolling is regarded as an important morphological trait in wheat breeding. Moderate leaf rolling is helpful to keep leaves upright and improve the photosynthesis of plants, leading to increased yield. However, studies on the identification of genomic regions/genes associated with rolling leaf have been reported less frequently in wheat. In this study, a rolling leaf mutant, T73, which has paired spikelets, dwarfism, and delayed heading traits, was obtained from a common wheat landrace through ethyl methanesulfonate mutagenesis. The rlT73 mutation caused an increase in the number of epidermal cells on the abaxial side and the shrinkage of bulliform cells on the adaxial side, leading to an adaxially rolling leaf phenotype. Genetic analysis showed that the rolling leaf phenotype was controlled by a single recessive gene. Further Wheat55K single nucleotide polymorphism array-based bulked segregant analysis and molecular marker mapping delimited rlT73 to a physical interval of 300.29-318.33 Mb on the chromosome arm 1BL in the Chinese Spring genome. We show that a point mutation at the miRNA165/166 binding site of the HD zipper class III transcription factor on 1BL altered its transcriptional level, which may be responsible for the rolling leaf phenotype. Our results suggest the important role of rlT73 in regulating wheat leaf development and the potential of miRNA-based gene regulation for crop trait improvement.

Enhanced SA and Ca2+ signaling results in PCD-mediated spontaneous leaf necrosis in wheat mutant wsl.

Leaf is the major photosynthesis organ and the key source of wheat (Triticum aestivum L.) grain. Spotted leaf (spl) mutant is a kind of leaf lesion mimic mutants (LMMs) in plants, which is an ideal material for studying the mechanisms of leaf development. In this study, we report the leaf abnormal development molecular mechanism of a spl mutant named white stripe leaf (wsl) derived from wheat cultivar Guomai 301 (WT). Histochemical observation indicated that the leaf mesophyll cells of the wsl were destroyed in the necrosis regions. To explore the molecular regulatory network of the leaf development in mutant wsl, we employed transcriptome analysis, histochemistry, quantitative real-time PCR (qRT-PCR), and observations of the key metabolites and photosynthesis parameters. Compared to WT, the expressions of the chlorophyll synthesis and photosynthesis-related homeotic genes were repressed; many genes in the WRKY transcription factor (TF) families were highly expressed; the salicylic acid (SA) and Ca2+ signal transductions were enhanced in wsl. Both the chlorophyll contents and the photosynthesis rate were lower in wsl. The contents of SA and reactive oxygen species (ROS) were significantly higher, and the leaf rust resistance was enhanced in wsl. Based on the experimental data, a primary molecular regulatory model for leaf development in wsl was established. The results indicated that the SA accumulation and enhanced Ca2+ signaling led to programmed cell death (PCD), and ultimately resulted in spontaneous leaf necrosis of wsl. These results laid a solid foundation for further research on the molecular mechanism of leaf development in wheat.

Heredity and gene mapping of a novel white stripe leaf mutant in wheat

Spotted leaf (spl) mutant is a type of leaf lesion mimic mutants in plants. We obtained some lesion mimic mutants from ethyl methane sulfonate (EMS)-mutagenized wheat (Triticum aestivum L.) cultivar Guomai 301 (wild type, WT), and one of them was named as white stripe leaf (wsl) mutant because of the white stripes on its leaves. Here we report the heredity and gene mapping of this novel wheat mutant wsl. There are many small scattered white stripes on the leaves of wsl throughout its whole growth period. As the plants grew, the white stripes became more severe and the necrotic area expanded. The mutant wsl grew only weakly before the jointing stage and gradually recovered after jointing. The length and width of the flag leaf, spike number per plant and thousand-grain weight of wsl were significantly lower than those of the WT. Genetic analysis indicated that the trait of white stripe leaf was controlled by a recessive gene locus, named as wsl, which was mapped on the short arm of chromosome 6B by SSR marker assay. Four SSR markers in the F2 population of wsl×CS were linked to wsl in the order of Xgpw1079-Xwmc104-Xgwm508-wsl-Xgpw7651 at 7.1, 5.2, 8.7, and 4.4 cM, respectively and three SSR markers in the F2 population of wsl×Jimai 22 were linked to wsl in the order of Xgwm508-Xwmc494-Xgwm518-wsl at 3.5, 1.6 and 8.2 cM, respectively. In comparison to the reference genome sequence of Chinese Spring (CS), wsl is located in a 91-Mb region from 88 Mb (Xgwm518) to 179 Mb (Xgpw7651) on chromosome 6BS. Mutant wsl is a novel germplasm for studying the molecular mechanism of wheat leaf development.

Identification and characterization of a serine protease from wheat leaves

A putative serine protease with a potential role in the plant biotic and abiotic stress response was purified from wheat leaf apoplastic fluid and partially characterized. Following two-dimensional electrophoresis a protein of Mr = 75 k and a pI of 4.2 to 4.5 was observed. This protein displayed in-gel protease activity and was specifically inhibited by phenylmethanesulfonyl fluoride and partially inhibited by Ca2+ and Zn2+, but not by E-64 or leupeptin. An internal tryptic fragment of 13 amino acids was identified by MALDI QqTOF MS/MS, and this peptide showed a high level of homology (85–100 % identity) to a highly conserved region of known plant subtilisin-like proteases. We demonstrated that the protease activity increased until a late stage of wheat leaf development and increased in response to heat shock. In both cases Rubisco large subunit was degraded with time. Protease activity was also increased during biotic stress. Leaves challenged with leaf rust (Puccinia triticina), showed an approximately three fold increase in protease activity during an incompatible interaction, compared to activity in mock-inoculated leaves and to leaves in a compatible leaf rust interaction. These results suggest that the expression of this serine protease could be involved in the defense response against both abiotic and biotic stresses.

The involvement of expansins in response to water stress during leaf development in wheat

Expansins are cell wall proteins that are generally considered to be the key regulator of cell wall extension during plant growth. In this study, we used two different wheat (Triticum aestivum L.) cultivars to demonstrate that expansins are involved in wheat leaf growth and response to water stress, by regulating the expansin activity and cell wall susceptibility to expansins. Expansin activity was associated with the relative elongation rate of leaves during leaf development, suggesting their involvement in leaf elongation. Moreover, cell wall extension characteristics and expansin gene transcription were closely involved in the leaf cell elongation region. Water stress restrains leaf growth, but the growth rate of leaves was changed after rehydration, which is consistent with the response of expansin activity to water stress. Meanwhile, increased cell wall susceptibility to expansin by water deficit played an important role in maintaining cell wall extension. Furthermore, the expansin activity in drought-resistant cultivar HF9703 was always higher than that in drought-sensitive cultivar 921842 under water stress condition, which may be correlated with the higher expansin gene expression in HF9703 versus 921842. These data provide evidence for a role of expansins in the growth and response of wheat leaves to water stress.

Effect of light intensity on the age dependence of nonphotochemical fluorescence quenching in wheat leaf

The effects of actinic light (AL) intensity on the age dependence of nonphotochemical fluorescence quenching (qN) and effective quantum yield in PSII (ΦPSII) were studied in continuously illuminated wheat leaves of the upper tier. Regular changes were revealed in both age dependence of qN at elevated AL intensities and light curves of qN. These changes are related to alterations in strategies of redistribution and use of absorbed light energy by the photosynthetic apparatus at different stages of wheat leaf development. Unlike ΦPSII, qN as a parameter was more sensitive to the differences in the leaf age at a certain range of light intensities. At the same time, the stability of qN at moderate light intensities may serve as an indication of leaf maturity.

Identification and quantitative expression of cytokinin regulatory genes during seed and leaf development in wheat

Cytokinins are intimately involved in plant growth and development and their concentration is known to change dramatically during early stages of seed development. We propose that the concentration of active cytokinin may be coordinately regulated by specific member(s) of the multi-gene families encoding biosynthesis (isopentenyl transferase, IPT), catabolism (cytokinin oxidase, CKX), and metabolism (zeatin glucosyltransferases (ZOG) and β-glucosidase (GLU)) genes. Our qRT-PCR data for 22 putative genes showed that the expression patterns of individual members of the Triticum aestivum (Ta)IPTs, TaCKXs, TaZOGs, and TaGLUs multi-gene families were tissue and development specific during seed and flag leaf development, with up to 90-fold changes in mRNA level. Key genes that may be involved in seed yield determination have been identified. Keywords: Wheat, flag leaf, cytokinin genes, quantitative expression, qRT-PCR

Developmental stage-specific multi-subunit plastid RNA polymerases (PEP) in wheat.

Most photosystem I and II plastid genes are transcribed by a plastid encoded Escherichia coli-like RNA polymerase (PEP). In this study, we show that both promoter selectivity and light-dependency of PEP change dramatically during development in wheat leaves. In the leaf tip, psbA and psbD promoter activities are light induced, whilst psbC, psbE and 16S rRNA promoters do not function efficiently irrespective of light conditions. In contrast to the leaf tip, in the basal portion all PEP promoters studied function in the dark as well as the light, except for psbD. Using in vitro transcription, we found that PEP in the illuminated leaf tip can initiate transcription from the -35 destructed psbA promoter, but the -35 element is essential for transcription in the basal portion. There is an extended -10 element in the psbA promoter, recognized by the PEP in the illuminated leaf tip or purified sigma 70-type Escherichia coli RNA polymerase but not by the PEP in the leaf base. These results suggest that during wheat leaf development, PEP in the leaf base that is functional for most PEP promoters even in the dark is replaced by the light-dependent PEP selectively transcribing the psbA and psbD promoters.

The Effect of Day to Night Temperature Variation on Leaf Development in Wheat

SummaryThe rate of leaf development in wheat is related to time and temperature in units of degree-days (DD) leaf−1 (phyllochron). Experiments were conducted in controlled environment chambers to study the effect of day to night variation in temperature on leaf development in two wheat cultivars, Penawawa and Stephens. Plants were grown at constant 20°C, and in eight day/night temperature ranges as wide as 8/32°C to 32/8°C, all with a mean temperature of 20°C. The leaf number on the main stems was counted (in Haun units) every other day, from the emergence of the 2nd leaf until the emergence of the 5th leaf. Leaf phyllochron values were derived from the inverse of the slopes of the linear regression of leaf number on DD. Phyllochron values ranged from 99 to 153 DD leaf−1. The phyllochron values were greater when higher temperatures were imposed at night under extreme day to night temperature treatment.

Mitochondria Increase Three-Fold and Mitochondrial Proteins and Lipid Change Dramatically in Postmeristematic Cells in Young Wheat Leaves Grown in Elevated CO2.

A dramatic stimulation in mitochondrial biogenesis during the very early stages of leaf development was observed in young wheat plants (Triticum aestivum cv Hereward) grown in elevated CO2 (650 [mu]L L-1). An almost 3-fold increase in the number of mitochondria was observed in the very young leaf cells at the base of the first leaf of a 7-d-old wheat plant. In the same cells large increases in the accumulation of a mitochondrial chaperonin protein and the mitochondrial 2-oxoglutarate dehydrogenase complex and pyruvate dehydrogenase complex were detected by immunolabeling. Furthermore, the basal segment also shows a large increase in the rate of radiolabeling of diphosphatidylglycerol, a lipid confined to the inner mitochondrial membrane. This dramatic response in very young leaf cells to elevated CO2 suggests that the numerous documented positive effects of elevated CO2 on wheat leaf development are initiated as early as 12 h postmitosis.

Effects of ozone on the photosynthetic apparatus and leaf proteins during leaf development in wheat

ABSTRACTLeaves of Triticum aestivum cv. Avalon were grown in an atmosphere that contained 150 nmole mol‐1 ozone for 7h each day. After leaves had reached maximum size, the leaf blade was divided into three sections to provide tissue of different age, the youngest at the base of the blade and the oldest at the leaf tip. The ozone treatment was found to decrease significantly the light‐saturated rate and quantum yield of CO2 assimilation and the maximum quantum yield of photosystem II photochemistry in the oldest leaf section. No effects were found on the basal and middle sections of the leaf. These ozone‐induced decreases in the photosynthetic parameters were associated with decreases in the efficiency of utilization of light for CO2 assimilation at the photon flux density under which the leaves were grown. The depression in photosynthetic performance of tissue near the leaf tip was accompanied by large decreases in the contents of total, soluble and thylakoid proteins and chlorophyll. There was also found to be a preferential loss of ribulose‐1,5‐carboxylase‐oxygenase. These ozone‐induced changes in chlorophyll and protein contents and the photosynthetic activities of the leaf tissue were similar to changes normally associated with leaf senescence. Two‐dimensional polyacrylamide gel analyses of leaf proteins demonstrated the loss of some minor, and unidentified, proteins, whilst another group of minor proteins appeared. It is concluded that daily exposure of the leaf to 150 nmol mol‐1 ozone for 7h had no effect on the development of the photosynthetic apparatus and its activities during leaf expansion, but it did promote the onset of premature senescence in fully expanded tissue that resulted in a loss of pigments, proteins and photosynthetic capacity and efficiency.

Phyllochron Change in Winter Wheat with Planting Date and Environmental Changes

AbstractThe phyllochron (degree‐days/leaf) of wheat (Triticum aestivum L.) differs with planting dates and latitudes. An understanding of the causes for these differences is needed to model the development of wheat crop canopies. Stephens and Yamhill winter wheat cultivars were planted on a range of dates in outdoor pots and in field plantings to study the relationship of phyllochron to the daylength and mean air temperature at seedling emergence. Both cultivars had a nearly constant phyllochron for a given planting in both pot and field plantings until 600 cumulated degree‐days (CDD), which was about the time of double ridge formation. Phyllochron values were different, however, for the different planting dates. At about 600 CDD the phyllochron increased in 18 of 20 cultivar‐planting date combinations. Fifty to 60% of the variation in phyllochron prior to double ridge formation could be normalized by either the thermo/photo ratio at seedling emergence (mean temperature to photoperiod) or by the rate of change of photoperiod. These two methods have been suggested previously to normalize phyllochron for differences due to different planting dates. After 600 CDD the phyllochron was not related to thermo/photo ratio, the rate of change of photoperiod, maximum or minimum temperatures, photoperiod or its inverse, or the intensity of solar radiation. Thus, use of a constant value for phyllochron in dynamic crop models of wheat leaf development is not appropriate for all circumstances.

Mitochondrial gene expression during wheat leaf development

The expression of specific mitochondrial, chloroplast and nuclear genes has been investigated in leaves of 7-d-old light-grown wheat (Triticum aestivum cv. Maris Dove). In the wheat leaf there is a spatial separation of a temporal sequence of development from the basal meristem to the distal mature, photosynthetically competent cells. This sequence of cellular differentiation is paralleled by a functional differentiation in which the energy supply changes from oxidative phosphorylation in the non-green meristematic cells to a combined dependence on oxidative and photophosphorylation in the photosynthesizing cells. The changes in copy number per cell and expression of mitochondrial genes have been investigated in successive sections of the wheat leaf using quantitative DNA-DNA and DNA-RNA filter and protein-binding techniques. The abundance of specific mitochondrial genes (cox II.cob andatp A) per cell was found to decrease between five- and tenfold within the basal (1 cm) section of the leaf and then remain constant to the distal tip. The relative abundances of specific mitochondrial transcripts (cox I,cox II,cob andatp A) were found to decrease in successive sections from the basal meristem to the distal tip (from a relative value of 100% to 5-40%). In contrast, transcripts of chloroplast genes and nuclear genes encoding chloroplast polypeptides (psb A,rbc L andrbc S) were found to increase steadily in progressive leaf sections (from a relative value of 0-2% to 100%). The steady-state level of the α-subunit of the mitochondrial F1 ATPase was found to remain constant along the length of the leaf. Possible sites at which the regulation of organellar gene expression is coordinated during the development of photosynthetic competence within the wheat leaf are discussed.