How rice defeats the floodwaters: Deepwater rice varieties grow taller when flooded, in a growth response driven by the plant hormones gibberellin and ethylene. This keeps the leaves above the water. Kuroha et al. identified the genes underlying this phenotype, which encode a component of the gibberellin biosynthetic pathway and its regulatory ethylene-responsive transcription factor. This genetic relay drives growth of the plant stem internodes in response to flooding. Modern cultivated deepwater rice, which has been domesticated for adaptation to the monsoon season of Bangladesh, emerged from the genetic variation found in wild rice strains over a broader geographic region. Science , this issue p. 181

The plasma membrane is considered to be the primary site of injury when plant cells are subjected to extracellular freezing. In order for plants or plant cells to acquire freezing tolerance, it is, thus, necessary that the plasma membrane increases its cryostability during freeze‐thaw excursion. During cold acclimation both under natural and artificial conditions, there are compositional, structural and functional changes occurring in the plasma membrane, many, if not all, of which ultimately contribute to increased stability of the plasma membrane under freezing conditions. In addition, changes in the cytosol or intracellular compartments also affect the cryobehaviour of the plasma membrane during freeze‐induced dehydration. Although many alterations occurring during cold acclimation influence the cryobehaviour of the plasma membrane comprehensively, recent advances in functional genomics approaches provide interesting information on the function of specific proteins for plasma membrane behaviour under freezing conditions.

Plant freezing tolerance involves the prevention of lethal freeze-induced damage to the plasma membrane. We hypothesized that plant freezing tolerance involves membrane resealing, which, in animal cells, is accomplished by calcium-dependent exocytosis following mechanical disruption of the plasma membrane. In Arabidopsis thaliana protoplasts, extracellular calcium enhanced not only freezing tolerance but also tolerance to electroporation, which typically punctures the plasma membrane. However, calcium did not enhance survival when protoplasts were exposed to osmotic stress that mimicked freeze-induced dehydration. Calcium-dependent freezing tolerance was also detected with leaf sections in which ice crystals intruded into tissues. Interestingly, calcium-dependent freezing tolerance was inhibited by extracellular addition of an antibody against the cytosolic region of SYT1, a homolog of synaptotagmin known to be a calcium sensor that initiates exocytosis. This inhibition indicates that the puncture allowing the antibody to flow into the cytoplasm occurs during freeze/thawing. Thus, we propose that calcium-dependent freezing tolerance results from resealing of the punctured site. Protoplasts or leaf sections isolated from Arabidopsis SYT1-RNA interference (RNAi) plants lost calcium-dependent freezing tolerance, and intact SYT1-RNAi plants had lower freezing tolerance than control plants. Taken together, these findings suggest that calcium-dependent freezing tolerance results from membrane resealing and that this mechanism involves SYT1 function.

Microdomains in the plasma membrane (PM) have been proposed to be involved in many important cellular events in plant cells. To understand the role of PM microdomains in plant cold acclimation, we isolated the microdomains as detergent-resistant plasma membrane fractions (DRMs) from Arabidopsis seedlings and compared lipid and protein compositions before and after cold acclimation. The DRM was enriched in sterols and glucocerebrosides, and the proportion of free sterols in the DRM increased after cold acclimation. The protein-to-lipid ratio in the DRM was greater than that in the total PM fraction. The protein amount recovered in DRMs decreased gradually during cold acclimation. Cold acclimation further resulted in quantitative changes in DRM protein profiles. Subsequent mass spectrometry and Western blot analyses revealed that P-type H⁺-ATPases, aquaporins and endocytosis-related proteins increased and, conversely, tubulins, actins and V-type H⁺-ATPase subunits decreased in DRMs during cold acclimation. Functional categorization of cold-responsive proteins in DRMs suggests that plant PM microdomains function as platforms of membrane transport, membrane trafficking and cytoskeleton interaction. These comprehensive changes in microdomains may be associated with cold acclimation of Arabidopsis.

Significance: This study investigates a previously unidentified cysteine-rich peptide (CRP). CRPs have diverse roles in plant growth and development, such as control of stomata density and guidance of pollen-tube elongation. Despite numerous studies on CRPs in Arabidopsis thaliana , there are still many peptides with unknown function. We identify a previously unidentified rice CRP named Regulator of Awn Elongation 2 (RAE2) and show that it is cleaved specifically in the spikelet to promote awn elongation. We demonstrate that RAE2 was a target of selection during domestication, contributing to loss of awns in Asian but not African rice. The discovery of RAE2 simultaneously deepens our understanding of plant developmental pathways and lends insight into the complex processes underlying cereal domestication.