# Integrated metabolome and transcriptome profiling demonstrates dynamic regulatory roles of hormones in direct-seeding rice

## TL;DR

This study explores how hormones and metabolites work together to improve seedling growth in rice planted directly in the field.

## Contribution

The study reveals new insights into how hormone balance and metabolic changes enhance rice seedling emergence under challenging conditions.

## Key findings

- CS2022 rice accumulates more cytokinins and lysine, promoting faster germination.
- CS2022 maintains a higher GA20/ABA ratio through precursor accumulation and ABA deactivation.
- Lipid remodeling involving sphingolipids and waxes may improve hypoxia tolerance in CS2022.

## Abstract

Direct-seeding rice faces the prominent challenge of low seedling emergence vigor, particularly under deep-sowing mechanical resistance and hypoxic conditions. Although some physiological traits are known, the systemic molecular networks determining superior emergence remain elusive.

Here, we integrated metabolomic and transcriptomic analyses to compare the elite direct-seeding variety ChongShang2022 (CS2022) with the control Huxiangruan450 (HXR450).

Weighted gene co-expression network analysis (WGCNA) identified germination-associated metabolic modules. Hub metabolite analysis revealed that the accelerated germination of CS2022 correlates with a higher accumulation of cytokinins (zeatin and cis-zeatin-9-N-glucoside), known for antagonizing abscisic acid (ABA)-induced dormancy, alongside key amino acids (e.g., L-lysine) and structural sphingolipids. Physiological validation confirmed the functional significance of these hubs, demonstrating that exogenous trans-zeatin and L-lysine significantly promoted seed germination in a dose-dependent manner. Notably, CS2022 exhibited heightened sensitivity, achieving maximal promotion at concentrations approximately 10-fold lower than HXR450. Targeted LC-MS/MS assays further demonstrated that CS2022 maintains a significantly higher GA20/ABA ratio during germination by accumulating the key precursor GA20 and deactivating free ABA into ABA-glucosyl ester. This hormonal homeostasis couples with elevated α-amylase activity, accelerating energy mobilization. At the seedling stage, multi-omics integration suggests an optimized growth-defense trade-off in CS2022. Auxin signaling supports rapid elongation, while the upregulation of jasmonic acid (JA) precursor transcripts contrasts with restricted accumulation of bioactive signals (e.g., JA-Ile). This potential signal buffering mechanism likely mitigates growth arrest. Additionally, lipid remodeling involving sphingolipids and waxes may contribute to hypoxia tolerance. Altogether, this study delineates a correlative regulatory network where dynamic hormone buffering, redirected metabolic flux, and adaptive lipid remodeling synergistically maximize direct-seeding rice emergence vigor, providing mechanistic insights and candidate modules for breeding.