Male-female crosstalk during pollen germination, tube growth and guidance, and double fertilization.

Plant growth and development are controlled by a delicate balance of hormonal cues. Growth-promoting hormones and growth-inhibiting counterparts often antagonize each other in their action, but the molecular mechanisms underlying these events remain largely unknown. Here, we report a cross-talk mechanism that enables a receptor-like kinase, FERONIA (FER), a positive regulator of auxin-promoted growth, to suppress the abscisic acid (ABA) response through activation of ABI2, a negative regulator of ABA signaling. The FER pathway consists of a FER kinase interacting with guanine exchange factors GEF1, GEF4, and GEF10 that, in turn, activate GTPase ROP11/ARAC10. Arabidopsis mutants disrupted in any step of the FER pathway, including fer, gef1gef4gef10, or rop11/arac10, all displayed an ABA-hypersensitive response, implicating the FER pathway in the suppression mechanism. In search of the target for the FER pathway, we found that the ROP11/ARAC10 protein physically interacted with the ABI2 phosphatase and enhanced its activity, thereby linking the FER pathway with the inhibition of ABA signaling.

https://www.pnas.org/content/pnas/109/36/14693.full.pdf

FERONIA receptor kinase pathway suppresses abscisic acid signaling in Arabidopsis by activating ABI2 phosphatase

Receptor-like kinase FERONIA (FER) plays a crucial role in plant response to small molecule hormones [e.g., auxin and abscisic acid (ABA)] and peptide signals [e.g., rapid alkalinization factor (RALF)]. It remains unknown how FER integrates these different signaling events in the control of cell growth and stress responses. Under stress conditions, increased levels of ABA will inhibit cell elongation in the roots. In our previous work, we have shown that FER, through activation of the guanine nucleotide exchange factor 1 (GEF1)/4/10-Rho of Plant 11 (ROP11) pathway, enhances the activity of the phosphatase ABA Insensitive 2 (ABI2), a negative regulator of ABA signaling, thereby inhibiting ABA response. In this study, we found that both RALF and ABA activated FER by increasing the phosphorylation level of FER. The FER loss-of-function mutant displayed strong hypersensitivity to both ABA and abiotic stresses such as salt and cold conditions, indicating that FER plays a key role in ABA and stress responses. We further showed that ABI2 directly interacted with and dephosphorylated FER, leading to inhibition of FER activity. Several other ABI2-like phosphatases also function in this pathway, and ABA-dependent FER activation required PYRABACTIN RESISTANCE (PYR)/PYR1-LIKE (PYL)/REGULATORY COMPONENTS OF ABA RECEPTORS (RCAR)-A-type protein phosphatase type 2C (PP2CA) modules. Furthermore, suppression of RALF1 gene expression, similar to disruption of the FER gene, rendered plants hypersensitive to ABA. These results formulated a mechanism for ABA activation of FER and for cross-talk between ABA and peptide hormone RALF in the control of plant growth and responses to stress signals.

https://www.pnas.org/content/pnas/113/37/E5519.full.pdf

FERONIA interacts with ABI2-type phosphatases to facilitate signaling cross-talk between abscisic acid and RALF peptide in Arabidopsis.

CrRLK1L receptor-like kinases: not just another brick in the wall.

A novel pollen-pistil interaction conferring high-temperature tolerance during reproduction via CLE45 signaling.

Double fertilization in angiosperms involves several successive steps, including guidance and reception of the pollen tube and male-female gamete recognition. Each step entails extensive communication and interaction between two different reproductive cell or tissue types. Extensive research has focused on the pollen tube, namely, its interaction with the stigma and reception by maternal cells. Little is known, however, about the mechanism by which the gametes recognize each other and interact to form a zygote. We report that an ankyrin repeat protein (ANK6) is essential for fertilization, specifically for gamete recognition. ANK6 (At5g61230) was highly expressed in the male and female gametophytes before and during but not after fertilization. Genetic analysis of a T-DNA insertional mutant suggested that loss of function of ANK6 results in embryonic lethality. Moreover, male-female gamete recognition was found to be impaired only when an ank6 male gamete reached an ank6 female gamete, thereby preventing formation of homozygous zygotes. ANK6 was localized to the mitochondria, where it interacted with SIG5, a transcription initiation factor previously found to be essential for fertility. These results show that ANK6 plays a central role in male-female gamete recognition, possibly by regulating mitochondrial gene expression.

https://www.pnas.org/content/pnas/107/51/22332.full.pdf

ANK6, a mitochondrial ankyrin repeat protein, is required for male-female gamete recognition in Arabidopsis thaliana

This research evaluates the mechanical properties of a variety of binary In-Sn alloys as potential candidates for low temperature electronic joints. The tensile and hardness tests of as-cast In-5Sn, In-12.5Sn, In-25Sn, In-30Sn, In-35Sn, In-40Sn, In-50Sn, In-60Sn, In-80Sn (wt.%) were assessed at room temperature and compared to those of pure In and Sn. The ultimate tensile strength (UTS) increased from 4.2 MPa to 37.8 MPa with increasing tin content in the alloys under the testing condition of 18 mm/min and the results showed little difference under a lower strain rate (1.8 mm/min). Most compositions showed good ductility in tensile testing with an average of 40% elongation. A melting point range of 119.3 °C to 194.9 °C for tested alloys was measured using differential scanning calorimetry (DSC). The microstructure investigated by scanning electron microscopy (SEM) was discussed with respect to the mechanical properties and it has been found that the presence of the Sn-rich γ-InSn4 phase in the microstructure has a significant impact on mechanical properties. The fundamental data from this study can be used for the development of new low temperature In-Sn alloys.

/pdf/mechanical-properties-and-microstructure-of-binary-in-sn-i0b7679f.pdf

Mechanical Properties and Microstructure of Binary In-Sn Alloys for Flexible Low Temperature Electronic Joints

Abstract Indium-based solder alloys are considered candidates for the next generation of low-temperature solder materials, especially for superconducting joints because of the properties of the β -In 3 Sn phase. The temperature-dependent phase transformation and thermal expansion behaviour of two different solder compositions including In-35Sn (in wt.%) and In-25.6Sn have been characterised using an in situ synchrotron powder X-ray diffraction method. The c-axis of the β -In 3 Sn unit cell in the In-35Sn alloy exhibited a complex relationship with increasing temperature compared to the positive increasing trend in In-25.6Sn due to the temperature-dependent solubility of Sn in β -In 3 Sn and change in the volume fraction of phases commencing at 80°C. In situ heating scanning electron microscopy recorded a real-time melting-solidification microstructure variation and phase transition during annealing at 90°C that was further analysed using energy dispersive X-ray spectroscopy. The observations are discussed with respect to the lattice parameters of the γ -InSn 4 and β -In 3 Sn phases and the proportions and composition of both phases present within the alloys. 

/pdf/the-temperature-dependent-phase-transformation-and-145clr0p.pdf

The Temperature-Dependent Phase Transformation and Microstructural Characterisation in In-Sn Solder Alloys

The Effect of Temperature on the Electrical Resistivity of Sn-Bi Alloys

Alloys based on the Sn-Bi system are widely considered as the most promising candidates for low temperature solders (LTS) in the electronics industry due to their low liquidus temperature, non-toxicity and relatively low cost. However, implementation of LTS is complicated as they exhibit different characteristics from conventional Pb-free solders. While the solid solubility of alloying additions in Sn is typically <1 wt% in the current generation of Pb-free solders, the solubility of Bi in Sn ranges from less than 3 wt% at room temperature to 21 wt% at the eutectic temperature of 139°C. In consequence, the microstructure and properties of Sn-Bi solders change significantly under varying temperature during normal service, affecting reliability. Since these changes are time and temperature dependent, interpreting results obtained using ex-situ methods requires assumptions about the stability of the alloy during transitions from the test environment to the observation environment, leading to an incomplete understanding of these changes. To address this, in-situ synchrotron powder X-ray diffraction (PXRD) and in-situ scanning electron microscopy (SEM) techniques were developed to investigate the time-temperature dependent lattice and microstructure of hypo-eutectic Sn-37wt%Bi and near-eutectic Sn-57wt%Bi solder alloys. This made possible for the first time the observation of changes during temperature fluctuations. The study revealed that lattice and microstructure are highly sensitive to factors like temperature ramp rate and isothermal holding time, not previously considered. The results will impact the design of electronic circuitry and process parameters during electronics assembly to enhance reliability and performance. 

In-situ investigation of the time-temperature dependent lattice and microstructure of Sn-Bi alloys

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