Author Correction: Rice auxin influx carrier OsAUX1 facilitates root hair elongation in response to low external phosphate

Phosphite treatment can improve root biomass and nutrition use efficiency in wheat

Phosphite represents a reduced form of phosphate that belongs to a class of crop growth-promoting chemicals termed biostimulants. Previous research has shown that phosphite application can enhance root growth, but its underlying mechanism, especially during environmental stresses, remains elusive. To uncover this, we undertook a series of morphological and physiological analyses under nutrient, water and heat stresses following a foliar application in wheat. Non-invasive 3D imaging of root system architecture directly in soil using X-ray Computed Tomography revealed that phosphite treatment improves root architectural traits and increased root biomass. Biochemical and physiological assays identified that phosphite treatment significantly increases Nitrate Reductase (NR) activity, leaf photosynthesis and stomatal conductance, suggesting improved Nitrogen and Carbon assimilation, respectively. These differences were more pronounced under heat or drought treatment (photosynthesis and photosystem II stability) and nutrient deficiency (root traits and NR). Overall our results suggest that phosphite treatment improves the ability of plants to tolerate abiotic stresses through improved Nitrogen and Carbon assimilation, combined with improved root growth which may improve biomass and yield.

Different Responses in Root Water Uptake of Summer Maize to Planting Density and Nitrogen Fertilization

Modifying farming practices combined with breeding has the potential to improve water and nutrient use efficiency by regulating root growth, but achieving this goal requires phenotyping the roots, including their architecture and ability to take up water and nutrients from different soil layers. This is challenging due to the difficulty of in situ root measurement and opaqueness of the soil. Using stable isotopes and soil coring, we calculated the change in root water uptake of summer maize in response to planting density and nitrogen fertilization in a 2-year field experiment. We periodically measured root-length density, soil moisture content, and stable isotopes δ¹⁸O and δD in the plant stem, soil water, and precipitation concurrently and calculated the root water uptake based on the mass balance of the isotopes and the Bayesian inference method coupled with the Markov Chain Monte Carlo simulation. The results show that the root water uptake increased asymptotically with root-length density and that nitrogen application affected the locations in soil from which the roots acquired water more significantly than planting density. In particular, we find that reducing nitrogen application promoted root penetration to access subsoil nutrients and consequently enhanced their water uptake from the subsoil, while increasing planting density benefited water uptake of the roots in the topsoil. These findings reveal that it is possible to manipulate plant density and fertilization to improve water and nutrient use efficiency of the summer maize and the results thus have imperative implications for agricultural production.

Uncovering How Auxin Optimizes Root Systems Architecture in Response to Environmental Stresses

Since colonizing land, plants have developed mechanisms to tolerate a broad range of abiotic stresses that include flooding, drought, high salinity, and nutrient limitation. Roots play a key role acclimating plants to these as their developmental plasticity enables them to grow toward more favorable conditions and away from limiting or harmful stresses. The phytohormone auxin plays a key role translating these environmental signals into developmental outputs. This is achieved by modulating auxin levels and/or signaling, often through cross talk with other hormone signals like abscisic acid (ABA) or ethylene. In our review, we discuss how auxin controls root responses to water, osmotic and nutrient-related stresses, and describe how the synthesis, degradation, transport, and response of this key signaling hormone helps optimize root architecture to maximize resource acquisition while limiting the impact of abiotic stresses.

Primary root and root hair development regulation by OsAUX4 and its participation in the phosphate starvation response

Among the five members of AUX1/LAX genes coding for auxin carriers in rice, only OsAUX1 and OsAUX3 have been reported. To understand the function of the other AUX1/LAX genes, two independent alleles of osaux4 mutants, osaux4-1 and osaux4-2, were constructed using the CRISPR/Cas9 editing system. Homozygous osaux4-1 or osaux4-2 exhibited shorter primary root (PR) and longer root hair (RH) compared to the wild-type Dongjin (WT/DJ), and lost response to indoleacetic acid (IAA) treatment. OsAUX4 is intensively expressed in roots and localized on the plasma membrane, suggesting that OsAUX4 might function in the regulation of root development. The decreased meristem cell division activity and the downregulated expression of cell cycle genes in root apices of osaux4 mutants supported the hypothesis that OsAUX4 positively regulates PR elongation. OsAUX4 is expressed in RH, and osaux4 mutants showing longer RH compared to WT/DJ implies that OsAUX4 negatively regulates RH development. Furthermore, osaux4 mutants are insensitive to Pi starvation (-Pi) and OsAUX4 effects on the -Pi response is associated with altered expression levels of Pi starvation-regulated genes, and auxin distribution/contents. This study revealed that OsAUX4 not only regulates PR and RH development but also plays a regulatory role in crosstalk between auxin and -Pi signaling.

Rice Root Hair Phenotypes Imaged by Cryo-SEM

Cryo-scanning electron microscopy (cryo-SEM) was first introduced for scientific use in the 1980s. Since then, cryo-SEM has become a routine technique for studying the surfaces and internal structures of biological samples with a high water content. In contrast to traditional SEM, cryo-SEM requires no sample pretreatment processes; thus, we can obtain the most authentic images of the sample shape and structure. Cryo-SEM has two main steps: cryoprocessing of samples and scanning electron microscopy (SEM) observation. The cryoprocessing step includes preparation of the cooled slushing station, cooling of the preparation chamber, sample preparation, and sputtering. The sample is then transferred to an SEM cold stage for observation. We used cryo-SEM to study rice root hair tissues, but the methods and protocols can be applied to other root systems. This protocol optimizes the two key operation steps of reducing the humidity in the growth chamber and previewing the samples before sputtering and can more quickly obtain high-quality images.