Stomatal complex morphogenesis

Abstract: Drought stress is a major global constraint for crop production, and improving crop tolerance to drought is of critical importance. Direct selection of drought tolerance among genotypes for yield is limited because of low heritability, polygenic control, epistasis effects, and genotype by environment interactions. Crop physiology can play a major role for improving drought tolerance through the identification of traits associated with drought tolerance that can be used as indirect selection criteria in a breeding program. Carbon isotope ratio (δ13C, associated with water use efficiency), oxygen isotope ratio (δ18O, associated with transpiration), canopy temperature (CT), canopy wilting, and canopy coverage (CC) are promising physiological traits associated with improvement of drought tolerance. Genome-wide association studies (GWAS) are one of the genomic approaches to provide a high mapping resolution for complex trait variation such as those related to drought tolerance. The objectives of this research were to identify genomic regions and favorable alleles that contribute to drought-tolerant traits. A diverse panel consisting of 373 maturity group (MG) IV soybean accessions was evaluated for δ13C, δ18O, canopy wilting, canopy coverage, and canopy temperature in multiple environments. A set of 31,260 polymorphic SNPs with a minor allele frequency (MAF) ≥ 5% was used for association mapping of CT using the FarmCPU model. Association mapping identified 54 significant SNPs associated with δ13C, 47 significant SNPs associated with δ18O, 61 significant SNPs associated canopy wilting, 41 and 56 significant SNPs associated with CC for first and second measurements dates, respectively, and 52 significant SNPs associated with CT. Several genes were identified using these significant SNPs, and those genes had reported functions related to transpiration, water transport, growth, developmental, root development, response to abscisic acid stimulus, and stomatal complex morphogenesis. Favorable alleles from significant SNPs may be an important resource for pyramiding genes to improve drought tolerance and for identifying parental genotypes for use in breeding programs.

Abstract: Contents Summary000 I. Introduction000 II. Cytoskeleton and development of the stomatal complexes000 III. Cytoskeleton and stomatal cell shaping000 IV. Stomatal pore formation000 V. Substomatal cavity formation000 VI. Stomatal complex morphogenesis in mutants000 VII. Cytoskeleton dynamics in functioning stomata000 VIII. Mechanisms of microtubule organization in stomatal cells000 IX. Conclusions-perspectives000 References000 Summary Microtubules (MTs) and actin filaments (AFs) form highly organized arrays in stomatal cells that play key roles in the morphogenesis of stomatal complexes. The cortical MTs controlling the orientation of the depositing cellulose microfibrils (CMs) and affecting the pattern of local wall thickenings define the mechanical properties of the walls of stomatal cells, thus regulating accurately their shape. Besides, they are involved in determination of the cell division plane. Substomatal cavity and stomatal pore formation are also MT-dependent processes. Among the cortical MT arrays, the radial ones lining the periclinal walls are of particular morphogenetic importance. Putative MT organizing centers (MTOCs) function at their focal regions, at least in guard cells (GCs), or alternatively, these regions either organize or nucleate cortical MTs. AFs are involved in cell polarization preceding asymmetrical divisions, in determination of the cell division plane and final cell plate alignment and probably in transduction of stimuli implicated in stomatal complex morphogenesis. Mature kidney-shaped GCs display radial AF arrays, undergoing definite organization cycles during stomatal movement. They are involved in stomatal movement, probably by controlling plasmalemma ion-channel activities. Radial MT arrays also persist in mature GCs, but a role in stomatal function cannot yet be attributed to them.