Reloading DNA History in Rice Domestication

OsLC1, a transaldolase, regulates cell patterning and leaf morphology through modulation of secondary metabolism

Leaf morphogenesis is a crucial process in plants that governs essential physiological functions such as photosynthesis and transpiration. Despite significant advances in understanding leaf development, the mechanism of intricate cellular patterning remains elusive. We characterize the OsLC1 mutant, which displays a curly leaf phenotype alongside reductions in plant height and tiller number, which are indicative of multiple morphological abnormalities. Through map-based cloning, we identified OsLC1 as encoding a transaldolase (TA) protein, whose genetic variations in OsLC1 lead to the disruptions of cell patterning across the vasculature, bundle sheath cells, mesophyll, stomata, bulliform cells and sclerenchyma cells. OsLC1 exhibited TA activity and modulated metabolic flux to the shikimic pathway, thereby affecting phenylpropanoid metabolism. This regulation influenced lignin and flavonoid biosynthesis, ultimately modulating cellular pattern formation through perturbations to flavonoid-mediated auxin or lignin homeostasis. Notably, loss of OsLC1 function led to a reduction in leaf water status, which, along with abnormal cellular patterns in oslc1, caused leaf curling. Overall, our findings provide insights into the regulatory mechanisms underlying cell patterning in the leaf and offer valuable perspectives on leaf morphogenesis in rice.

Parallel Selection in Domesticated Atlantic Salmon from Divergent Founders Including on Whole-Genome Duplication-derived Homeologous Regions

Domestication and artificial selection for desirable traits have driven significant phenotypic changes and left detectable genomic footprints in farmed animals. Since the 1960s, intensive breeding has led to the rapid domestication of Atlantic salmon (Salmo salar), with multiple independent events that make it a valuable model for studying early domestication stages and the parallel evolution of populations of different origins subjected to similar selection pressures. Some aquatic species, including Atlantic salmon, have undergone whole-genome duplication (WGD), raising the possibility that genetic redundancy resulting from WGD has contributed to adaptation in captive environments, as seen in plants. Here, we examined the genomic responses to domestication in Atlantic salmon, focusing on potential signatures of parallel selection, including those associated with WGD. Candidate genomic regions under selection were identified by comparing whole-genome sequences from aquaculture and wild populations across 2 independently domesticated lineages (Western Norway and North America) using a genome-wide scan that combined 3 statistical methods: allele frequencies (FST), site frequency (Tajima's D), and haplotype differentiation (XP-EHH). These analyses revealed shared selective sweeps on identical SNPs in major histocompatibility complex (MHC) genes across aquaculture populations. This suggests that a combination of long-term balancing selection and recent human-induced selection has shaped MHC gene evolution in domesticated salmon. Additionally, we observed selective sweeps on a small number of gene pairs in homeologous regions originating from WGD, offering insights into how historical genome duplication events may intersect with recent selection pressures in aquaculture species.

Genetic mechanisms underlying diverse panicle architecture in rice

Rice panicle architecture exhibits remarkable diversity and is crucial in determining grain production. Recent advances in the understanding of the genetic mechanisms underlying panicle morphogenesis offer promising avenues for improving rice productivity. Here, I reviewed recent studies on the developmental regulatory genes responsible for panicle architecture and explored how these findings can be applied to crop breeding. I also discuss the potential of using wild Oryza genetic resources, highlighting their value not only for scientific exploration but also for breeding innovation. Isolating novel genes related to panicle development and understanding their function are essential for designing diverse panicle architectures by quantitative trait locus pyramiding or genome editing technology. The use of these genetic resources offers a sustainable means to improve rice plant architecture and their resilience to climate change.

The natural variation allele OsGSW3.2 in Oryza rufipogon is involved in brassinosteroid signaling and influences grain size and weight

Oryza rufipogon is the ancestor of cultivated rice and harbors many elite genes; thus, this plant is an important germplasm for improving rice varieties. Grain size is an important factor in determining rice yield and quality. In this study, we identified a natural variation allele from the O. rufipogon inbred line Huaye3 (HY3), which is located on chromosome 3 and named it GRAIN SIZE and WEIGHT 3.2 (OsGSW3.2). The OsGSW3.2 knockout (KO) mutant presented increased grain size and weight, which was associated with decreased chlorophyll content and long awns. The overexpression of OsGSW3.2HY3 caused a significant decrease in grain size and weight. OsGSW3.2 negatively regulates grain size through cell proliferation. Transcriptomic analysis of spikelet hulls from the KO lines and wild-type HY3 revealed that the differentially expressed genes (DEGs) were enriched mainly in plant-pathogen interactions, plant hormone signal transduction, and the plant MAPK signaling pathway, and so on. A laminar inclination experiment verified that OsGSW3.2 was involved in the BR signaling pathway. Yeast two-hybrid, BiFC, LAC, and pull-down experiments verified that OsGSW3.2 interacted with OsGSK4, which was related to BR signaling, in yeast and plant cells. OsGSW3.2 influenced rice grain size and weight via interaction with OsGSK4. Haplotype analysis of a core collection of cultivated rice revealed that transcriptional accumulation and differential SNPs in the coding region may influence grain size and weight. Our results provide new insight into the role of OsGSW3.2 in affecting grain size and weight, which will help elucidate the genetic basis of rice domestication.

Genetic dissection of a reduced seed-shattering trait acquired in rice domestication

Asian rice (Oryza sativa L.) was domesticated from wild rice (O. rufipogon Griff.). During rice domestication, the wild characteristic of seed-shattering behaviour was suppressed, enabling an efficient harvest with increased yield. Rice, a stable food for humans, is one of the most important crops consumed by billions of people, especially in Asian countries. With advances in molecular genetic studies, genes or loci involved in reduced seed shattering via the inhibition of abscission layer formation have been identified. The mutations alone showed no inhibitory effect on abscission layer formation in the wild rice O. rufipogon, but their combination enabled a stepwise change in the degree of seed shattering, which may be associated with advances in harvesting tools. In the early stages of rice domestication, the closed panicle formation and slight inhibition of the abscission layer resulted in complementary effects that increased harvesting efficiency. Furthermore, common and distinct loci were found to contribute to reduced seed shattering in groups of rice cultivars, indicating that mutations at seed-shattering loci are important information for tracing the process of rice domestication.

Deciphering key factors in pathogen-suppressive microbiome assembly in the rhizosphere

In a plant-microbe symbiosis, the host plant plays a key role in promoting the association of beneficial microbes and maintaining microbiome homeostasis through microbe-associated molecular patterns (MAMPs). The associated microbes provide an additional layer of protection for plant immunity and help in nutrient acquisition. Despite identical MAMPs in pathogens and commensals, the plant distinguishes between them and promotes the enrichment of beneficial ones while defending against the pathogens. The rhizosphere is a narrow zone of soil surrounding living plant roots. Hence, various biotic and abiotic factors are involved in shaping the rhizosphere microbiome responsible for pathogen suppression. Efforts have been devoted to modifying the composition and structure of the rhizosphere microbiome. Nevertheless, systemic manipulation of the rhizosphere microbiome has been challenging, and predicting the resultant microbiome structure after an introduced change is difficult. This is due to the involvement of various factors that determine microbiome assembly and result in an increased complexity of microbial networks. Thus, a comprehensive analysis of critical factors that influence microbiome assembly in the rhizosphere will enable scientists to design intervention techniques to reshape the rhizosphere microbiome structure and functions systematically. In this review, we give highlights on fundamental concepts in soil suppressiveness and concisely explore studies on how plants monitor microbiome assembly and homeostasis. We then emphasize key factors that govern pathogen-suppressive microbiome assembly. We discuss how pathogen infection enhances plant immunity by employing a cry-for-help strategy and examine how domestication wipes out defensive genes in plants experiencing domestication syndrome. Additionally, we provide insights into how nutrient availability and pH determine pathogen suppression in the rhizosphere. We finally highlight up-to-date endeavors in rhizosphere microbiome manipulation to gain valuable insights into potential strategies by which microbiome structure could be reshaped to promote pathogen-suppressive soil development.