Shahrokh Khanizadeh

Stone cell lignification is a key determinant of pear fruit texture and commercial quality, and this process has been reported to be tightly coupled to cellular glucose availability. However, how glucose dose‐dependently targets transcription factor phosphorylation during lignin biosynthesis remains largely unknown. Using yeast two‐hybrid library screening and phosphorylation assays, we found that PbSnRK1, a glucose‐responsive kinase, interacts with and directly phosphorylates PbTCP13, thereby participating in the regulation of stone cell lignification. PbSnRK1 serves as an energy‐status sensor linking glucose signalling to biphasic regulation of lignin metabolism in pear. Under low‐glucose conditions, activated PbSnRK1 phosphorylates the transcription factor PbTCP13 at Ser265, targeting it for 26S proteasome‐mediated degradation and thereby derepressing PbMYB11‐ PbCCR1 cascade associated with lignin biosynthesis. Under high‐glucose conditions, suppressed PbSnRK1 kinase activity results in PbTCP13 protein accumulation, which restricts excessive lignification by both repressing PbCCR1 transcription and physically interacting with PbMYB11 to inhibit its transactivation capacity. This PbSnRK1‐PbTCP13‐PbMYB11 cascade, balanced by glucose concentration, acts as a molecular switch that activates stone cell formation and lignification at low‐glucose levels during early fruit development, while restricting excessive lignification at high‐glucose levels during later stages, providing new mechanistic insights into energy‐coupled secondary wall metabolism in fleshy fruits.

Fruit texture is a critical determinant of pear fruit quality, consumer acceptance, and market value during both commercialization and postharvest storage. Excessive lignification during fruit development leads to the formation of abundant stone cells, resulting in a coarse texture and reduced eating quality. However, the molecular mechanisms underlying cultivar-dependent variation in stone cell content remain largely unclear. In this study, two pear cultivars with contrasting stone cell contents, Pyrus bretschneideri ’Dangshansu’ and Pyrus pyrifolia ’Kosui’, were used to investigate the transcriptional regulation of lignification and stone cell formation during fruit development. Comparative transcriptome analyses across multiple developmental stages identified a large number of differentially expressed genes between the two cultivars, particularly during the critical period of stone cell formation. Functional enrichment analyses revealed that these genes were mainly associated with phenylpropanoid biosynthesis, secondary cell wall formation, and lignin metabolic processes. Weighted gene co-expression network analysis (WGCNA) further identified stone cell-associated modules and key candidate regulators involved in lignification. Among these candidates, a previously uncharacterized bZIP transcription factor, bZIP4, was identified as a potential regulator of stone cell development. Functional analyses demonstrated that overexpression of bZIP4 significantly promoted lignin deposition and stone cell accumulation in pear callus, transiently transformed pear fruit, and transgenic Arabidopsis plants. Molecular assays showed that bZIP4 directly binds to the promoter of HCT32 and activates its transcription. Consistently, overexpression of HCT32 also resulted in enhanced lignin accumulation and increased stone cell content. Collectively, these findings reveal that the bZIP4-HCT32 regulatory module positively regulates lignification and stone cell formation during pear fruit development. This study provides new insights into the molecular basis of fruit texture formation and identifies promising targets for reducing stone cell content, thereby contributing to the genetic improvement of pear fruit quality and potentially enhancing postharvest performance.

SUMMARY: Stone cells are the brachysclereid cells in pear (Pyrus) fruit, consisting almost entirely of lignified secondary cell walls. They are distributed mainly near the fruit core and spread radially in the whole fruit. However, the development of stone cells has not been comprehensively characterized, and little is known about the regulation of stone cell formation at the transcriptomic, proteomic, and metabolomic levels. In the present study, we performed phenomic analysis on the stone cells and their associated vascular bundles distributed near the fruit cores. Transcriptomic, proteomic, and metabolomic analyses revealed a significant positive regulation of biological processes which contribute to the lignification and lignin deposition in stone cells near the fruit core, including sucrose metabolism and phenylalanine, tyrosine, tryptophan, and phenylalanine biosynthesis. We found many metabolites generated from the phenylpropanoid pathway contributing to the cell wall formation of stone cells near the fruit core. Furthermore, we identified a key transcription factor, PbbZIP48, which was highly expressed near the fruit core and was shown to regulate lignin biosynthesis in stone cells. In conclusion, the present study provides insight into the mechanism of lignified stone cell formation near the pear fruit core at multiple levels.

Lodging is an important limiting factor in wheat because it affects growth, yield and grain quality. Plant growth regulators (PGRs) are often used to restrain elongation of internodes, improve lodging traits, and protect yield potentials. An experiment was set up in the greenhouse at the Ottawa Research and Development Centre (ORDC) to study the effect of the selected PGRs (Manipulator, the active ingredient of which is chlormequat; and Palisade, the active ingredient of which is trinexapac-ethyl) on yield, stem height and morphological traits in six spring wheat cultivars (AC Carberry, AAC Scotia, Hoffman, Fuzion, FL62R1, and AW725). Both PGRs reduced plant height and caused a 6% to 48% reduction in the length of the second basal internode. The mixture of the two PGRs had a synergistic affect and made the stem shorter. The application of PGRs significantly reduced lodging, increased stem diameter, thickness, filling degree, and stem strength, and increased leaf relative chlorophyll content. However, application of PGRs significantly reduced grain yield, and the combination of the two PGRs (Manipulator and Palisade) had a synergistic effect and lowered the yield. In general, the effect of Palisade was more evident than that of Manipulator.

The study was conducted to evaluate in vitro pollen germination of 50 spring wheat (Triticum aestivum L.) accessions at three storage temperatures (23 °C, 5 °C, and -20 °C). Germination of the mature pollen was measured right after harvest (0 time), and 24, 48, and 72 h after storage (HAS). Differences in fresh pollen germination between accessions were significant and ranged from 21.15% to 1.09%. Pollen germination was the lowest at 24 h at room temperature. The pollens of 24 wheat accessions (AAC Scotia, AW636, AW725, AW780, AW804, AW822, AW823, Brookfield, BRS Pardela, ECSW05, ECSW38, ECSW48, ECSW49, ECSW69, Hoffman, Kleos, Major, Nass, 12NQW-237, 12NQW-413, 12NQW-414, 12NQW-436, 12NQW-754, and 12BW0374) were viable after 24 h when they were stored at 5 °C. Sub-zero temperature did not prolong pollen viability.

The Effect of Production Systems on Strawberry Quality | InTechOpen, Published on: 2017-03-15. Authors: Li Fan, Claudine Dubé and Shahrokh Khanizadeh