In vitro experiments and kinetic models of Arabidopsis pollen hydration mechanics show that MSL8 is not a simple tension-gated osmoregulator

The MYC transcription factor PbrMYC8 negatively regulates PbrMSL5 expression to promote pollen germination in Pyrus

The successful germination of pollen is essential for double fertilization in flowering plants. Mechanosensitive channels of small conductance (MscS-like, MSL) inhibit pollen germination and maintains cellular integrity of pollen during this process. Therefore, it is vital to carefully regulate the expression of MSL to promote successful pollen germination. Despite its importance, the molecular mechanisms governing MSL expression in plants remain poorly understood. Here, we had identified 15 MSL genes in the pear, among which PbrMSL5 was expressed in pollen development. Subcellular localization experiments revealed that PbrMSL5 was located in both plasma membrane and cytoplasm. Functional investigations, including complementation experiments using the atmsl8 mutant background, demonstrated the involvement of PbrMSL5 in preserving pollen cell integrity and inhibiting germination. Antisense oligonucleotide experiments further confirmed that PbrMSL5 suppressed pear pollen germination by reducing osmotic pressure and Cl- content. Yeast one-hybrid, electrophoretic mobility shift assays, and dual luciferase reporter assay elucidated that PbrMYC8 interacts directly with the N-box element, leading to the suppression of PbrMSL5 expression and promoted pollen germination. These results represented a significant advancement in unraveling the molecular mechanisms controlling plant MSL expression. This study showed valuable contribution to advancing our comprehension of the mechanism underlying pollen germination.

Structure and growth of plant cell walls

Plant cells build nanofibrillar walls that are central to plant growth, morphogenesis and mechanics. Starting from simple sugars, three groups of polysaccharides, namely, cellulose, hemicelluloses and pectins, with very different physical properties are assembled by the cell to make a strong yet extensible wall. This Review describes the physics of wall growth and its regulation by cellular processes such as cellulose production by cellulose synthase, modulation of wall pH by plasma membrane H+-ATPase, wall loosening by expansin and signalling by plant hormones such as auxin and brassinosteroid. In addition, this Review discusses the nuanced roles, properties and interactions of cellulose, matrix polysaccharides and cell wall proteins and describes how wall stress and wall loosening cooperatively result in cell wall growth.

Structural and molecular basis of pollen germination

Pollen germination is a prerequisite for double fertilization of flowering plants. A comprehensive understanding of the structural and molecular basis of pollen germination holds great potential for crop yield improvement. The pollen aperture serves as the foundation for most plant pollen germination and pollen aperture formation involves the establishment of cellular polarity, the formation of distinct membrane domains, and the precise deposition of extracellular substances. Successful pollen germination requires precise material exchange and signal transduction between the pollen grain and the stigma. Recent cytological and mutant analysis of pollen germination process in Arabidopsis and rice has expanded our understanding of this biological process. However, the overall changes in germination site structure and energy-related metabolites during pollen germination remain to be further explored. This review summarizes and compares the recent advances in the processes of pollen aperture formation, pollen adhesion, hydration, and germination between eudicot Arabidopsis and monocot rice, and provides insights into the structural basis and molecular mechanisms underlying pollen germination process.

Root osmotic sensing from local perception to systemic responses

Plants face a constantly changing environment, requiring fine tuning of their growth and development. Plants have therefore developed numerous mechanisms to cope with environmental stress conditions. One striking example is root response to water deficit. Upon drought (which causes osmotic stress to cells), plants can among other responses alter locally their root system architecture (hydropatterning) or orientate their root growth to optimize water uptake (hydrotropism). They can also modify their hydraulic properties, metabolism and development coordinately at the whole root and plant levels. Upstream of these developmental and physiological changes, plant roots must perceive and transduce signals for water availability. Here, we review current knowledge on plant osmotic perception and discuss how long distance signaling can play a role in signal integration, leading to the great phenotypic plasticity of roots and plant development.