Biology subjects

Khahani, B.

Publications and source records attributed to Khahani, B..

3 recordsLinked to original sources

bioRxiv2025

Temperature signals drive grass secondary cell wall thickening

In grasses, stem elongation is driven by intercalary meristems at node-internode junctions, where cells divide, elongate, and in some cell types secondary wall maturation. Cellulose is the predominant polymer in plant cells and the most abundant biopolymer on Earth. It is synthesized at the plasma membrane by multi-protein complexes that include CELLULOSE SYNTHASE A (CESA) proteins. To investigate the spatiotemporal regulation of cellulose deposition during development, we developed a CESA8 luciferase gene expression reporter system in Brachypodium distachyon. High bioluminescence was observed in stem nodes, a specific region of elongating internodes, and the inflorescence, indicating sites of active secondary wall deposition. Within internodes, luminescence followed a distinct pattern, with a "dark zone" directly above the node with minimal signal, followed by a "bright zone" approximately 5 mm above the node where bioluminescence peaked. Histological, biophysical, and transcript analysis confirmed that luminescence intensity correlates with thickened secondary cell walls, increased cellulose crystallinity, and elevated CESA8 transcript levels. Time-lapse imaging revealed that CESA8 expression follows a robust diurnal rhythm governed by thermocycles alone, with peak expression occurring in the early morning. Temperature pulse experiments revealed an immediate but transient response of CESA8 to temperature shifts, which we modeled as an incoherent feed-forward loop. Finally, we found a strong correlation between CESA8 expression and stem elongation, highlighting the role of secondary cell wall thickening in supporting upright growth. These findings provide new insights into the regulation of secondary wall formation and its integration with environmental cues, advancing our understanding of grass stem development. SIGNIFICANCEUnderstanding how grasses build strong stems is essential for improving biomass production and crop resilience. In grasses, stem elongation and secondary cell wall thickening occur in distinct zones, yet the precise timing and regulation of this process remain unclear. To investigate this phenomenon, we developed a real-time imaging system to track the expression of CESA8, a key gene involved in cellulose synthesis. Our findings reveal that secondary wall thickening follows a daily rhythm controlled by temperature rather than light. These insights provide a foundation for optimizing plant architecture in bioenergy crops, improving their efficiency and sustainability.

plant biology↗

bioRxiv2024

Impact of mutations in the HEADING DATE 1 gene on transcription and cell wall composition of rice

Plants utilize environmental information to modify their developmental trajectories for optimal survival and reproduction. Over a century ago, day length (photoperiod) was identified as a major factor influencing developmental transitions, particularly the shift from vegetative to reproductive growth. In rice, exposure to day lengths shorter than a critical threshold accelerates flowering, while longer days inhibit this process. This response is mediated by HEADING DATE 1 (Hd1), a zinc finger transcription factor that is central in the photoperiodic flowering network. Hd1 acts as a repressor of flowering under long days but functions as a promoter of flowering under short days. However, the transcriptional organization of this dual function is still not fully understood. In this study, we utilized RNA-Seq to analyze the transcriptome of hd1 mutants under both long and short day conditions. We identified genes involved in the phenylpropanoid pathway that are deregulated under long days in the mutant. Quantitative profiling of cell wall components and abiotic stress assays suggest that Hd1 is involved in processes considered unrelated to flowering control. This indicates that day length perception and responses are intertwined with physiological processes beyond flowering.

plant biology↗

bioRxiv2024

Shoring up the base: the development and regulation of cortical sclerenchyma in grass nodal roots

Plants depend on the combined action of a shoot-root-soil system to maintain their anchorage to the soil. Mechanical failure of any component of this system results in lodging, a permanent and irreversible inability to maintain vertical orientation. Models of anchorage in grass crops identify the compressive strength of roots near the soil surface as key determinant of resistance to lodging. Indeed, studies of disparate grasses report a ring of thickened, sclerenchyma cells surrounding the root cortex, present only at the base of nodal roots. Here, in the investigation of the development and regulation of this agronomically important trait, we show that development of these cells is uncoupled from the maturation of other secondary cell wall-fortified cells, and that cortical sclerenchyma wall thickening is stimulated by mechanical forces transduced from the shoot to the root. We also show that exogenous application of gibberellic acid stimulates thickening of lignified cell types in the root, including cortical sclerenchyma, but is not sufficient to establish sclerenchyma identity in cortex cells. Leveraging the ability to manipulate cortex development via mechanical stimulus, we show that cortical sclerenchyma development alters root mechanical properties and improves resistance to lodging. We describe transcriptome changes associated with cortical sclerenchyma development under both ambient and mechanically stimulated conditions and identify SECONDARY WALL NAC7 as a putative regulator of mechanically responsive cortex cell wall development at the root base.

plant biology↗