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Introduction: Transcriptomic divergence drives plant ecological adaptation. Upland rice is differentiated in drought tolerance from lowland rice during its adaptation to the drought‐prone environment. They provide a good system to learn the evolution of drought tolerance in rice. Methods and Results: We estimate morphological differences between the two rice ecotypes under well‐watered and drought conditions, as well as their genetic and transcriptomic divergences by the high‐throughput sequencing. Upland rice possesses higher expression diversity than lowland rice does. Thousands of genes exhibit expression divergences between the two rice ecotypes, which contributes to their morphological differences in drought tolerance. These transcriptomic divergences contribute to drought adaptation of upland rice during its domestication. Mutations in transcriptional regulatory regions, which cause presence and absence of cis‐elements, are the cause of expression divergence. About 15.3% transcriptionally selected genes also receive sequence‐based selection in upland or lowland ecotype. Some highly differentiated genes promote the transcriptomic divergence between rice ecotypes via gene co‐expression network. In addition, we also detected transcriptomic trade‐offs between drought tolerance and productivity. Discussion: Many key genes, which promote transcriptomic adaptation to drought in upland rice, have great prospective in breeding water‐saving and drought‐resistant rice. Meanwhile, appropriate strategies are required in breeding to overcome the potential transcriptomic trade‐off. [ABSTRACT FROM AUTHOR]

Summary: The growth and development of roots in plants depends on the specification and maintenance of the root apical meristem. Here, we report the identification of CBL, a gene required for embryo and root development in Arabidopsis, and encodes cystathionine beta‐lyase (CBL), which catalyzes the penultimate step in methionine (Met) biosynthesis, and which also led to the discovery of a previous unknown, but crucial, metabolic contribution by the Met biosynthesis pathway. CBL is expressed in embryos and shows quiescent center (QC)‐enriched expression pattern in the root. cbl mutant has impaired embryo patterning, defective root stem cell niche, stunted root growth, and reduces accumulation of the root master regulators PLETHORA1 (PLT1) and PLT2. Furthermore, mutation in CBL severely decreases abundance of several PIN‐FORMED (PIN) proteins and impairs auxin‐responsive gene expression in the root tip. cbl seedlings also exhibit global reduction in histone H3 Lys‐4 trimethylation (H3K4me3) and DNA methylation. Importantly, mutation in CBL reduces the abundance of H3K4me3 modification in PLT1/2 genes and downregulates their expression. Overexpression of PLT2 partially rescues cbl root meristem defect, suggesting that CBL acts in part through PLT1/2. Moreover, exogenous supplementation of Met also restores the impaired QC activity and the root growth defects of cbl. Taken together, our results highlight the unique role of CBL to maintain the root stem cell niche by cooperative actions between Met biosynthesis and epigenetic modification of key developmental regulators. Significance Statement: Growth and development depend on metabolic activities that properly support fundamental cellular functions, but mechanistic links are scarce. Here, we demonstrate that a quiescent center‐enriched CBL gene, encoding the second committed enzyme in methionine (Met) biosynthesis, plays a crucial role in root apical meristem maintenance by epigenetically influencing expression of the root master regulators PLETHORA (PTL1/2), elucidating a functional link between Met metabolic contribution and auxin‐dependent PLT‐mediated maintenance of root stem cell niche. [ABSTRACT FROM AUTHOR]