Summary: Rice (Oryza sativa) is the staple food for over half the world’s population. Drought stress imposes major constraints on rice yields. Intriguingly, labdane‐related diterpenoid (LRD) phytoalexins in maize (Zea mays) affect drought tolerance, as indicated by the increased susceptibility of an insertion mutant of the class II diterpene cyclase ZmCPS2/An2 that initiates such biosynthesis. Rice also produces LRD phytoalexins, utilizing OsCPS2 and OsCPS4 to initiate a complex metabolic network. For genetic studies of rice LRD biosynthesis the fast‐growing Kitaake cultivar was selected for targeted mutagenesis via CRISPR/Cas9, with an initial focus on OsCPS2 and OsCPS4. The resulting cps2 and cps4 knockout lines were further crossed to create a cps2x4 double mutant. Both CPSs also were overexpressed. Strikingly, all of the cv Kitaake cps mutants exhibit significantly increased susceptibility to drought, which was associated with reduced stomatal closure that was evident even under well‐watered conditions. However, CPS overexpression did not increase drought resistance, and cps mutants in other cultivars did not alter susceptibility to drought, although these also exhibited lesser effects on LRD production. The results suggest that LRDs may act as a regulatory switch that triggers stomatal closure in rice, which might reflect the role of these openings in microbial entry.

Rice (Oryza sativa) is a staple food crop and serves as a model cereal plant. It contains two biosynthetic gene clusters (BGCs) for production of labdane-related diterpenoids (LRDs), which serve important roles in combating biotic and abiotic stresses. While plant BGCs have been subject to genetic analyses, these have been largely confined to investigation of single genes. CRISPR/Cas9-mediated genome editing was used to precisely remove each of these BGCs, as well as simultaneously knock-out both BGCs. Deletion of the BGC from chromosome 2 (c2BGC), which is associated with phytocassane biosynthesis, but not that from chromosome 4 (c4BGC), which is associated with momilactone biosynthesis, led to a lesion mimic phenotype. This phenotype is dependent on two closely related genes encoding cytochrome P450 (CYP) mono-oxygenases, CYP76M7 and CYP76M8, from the c2BGC. However, rather than being redundant, CYP76M7 has been associated with production of phytocassanes, while CYP76M8 is associated with momilactone biosynthesis. Intriguingly, the lesion mimic phenotype is not present in a line with both BGCs deleted. These results reveal directional cross-cluster phytotoxicity, presumably arising from accumulation of LRD intermediates dependent on the c4BGC in the absence of CYP76M7 and CYP76M8, further highlighting their interdependent evolution and the selective pressures driving BGC assembly.

Chemotherapy resistance in colorectal cancer (CRC) remains a major obstacle in clinical oncology. Analysis of clinical specimens from chemotherapy-resistant patients revealed elevated CXCL7 expression in tumor-associated macrophages (TAMs). Through integrated in vitro and in vivo studies, we demonstrated that chemotherapy induces tumor cell-macrophage crosstalk, leading to CXCL7 upregulation in TAMs. Using a co-culture system, we observed that CXCL7+ macrophages confer chemoresistance to CRC cells. Mechanistic investigations revealed that CXCL7 activates the CXCR2 receptor on tumor cells, triggering interferon signaling and promoting serine metabolism through STAT1-dependent transcriptional upregulation of phosphoglycerate dehydrogenase (PHGDH), the key enzyme in serine biosynthesis. This metabolic reprogramming enhances the paracrine secretion of S-adenosyl methionine (SAM), which drives chemotherapy resistance. Furthermore, CXCL7-mediated the paracrine secretion of SAM in tumor cells, which in turn promotes M2 macrophage polarization and sustains CXCL7 expression in TAMs. Our findings reveal that a CXCL7-SAM feedback loop between tumor cells and macrophages establishes a chemoresistant niche. This interaction represents a promising therapeutic target for overcoming chemoresistance in CRC.

Breast cancer frequently metastasizes to the bone, but treatment options for bone metastatic breast cancer are limited. Amino acid metabolism is reprogrammed in the bone metastatic microenvironment, suggesting that it could represent a therapeutic vulnerability. In this study, we focused on the metabolism of hydroxyproline (Hyp), a key amino acid resulting from bone collagen degradation, which serves as a critical biomarker for bone metastases. Proline dehydrogenase 2 (PRODH2), the primary enzyme involved in Hyp metabolism, was significantly upregulated in clinical samples from breast cancer bone metastases. Notably, PRODH2-mediated Hyp metabolism drove osteoclast differentiation, enhancing collagen degradation and promoting breast cancer bone metastasis in vivo. Furthermore, PRODH2 facilitated tumor cell viability and osteoclast differentiation by upregulating the ferroptosis inhibitor SLC7A11 and the bone metastasis–related factor CXCL8 (IL8), respectively. Intriguingly, Hyp metabolism catalyzed by PRODH2 generated acetyl-CoA, which enhanced YY1 acetylation and thereby transcriptionally activated both SLC7A11 and IL8. Importantly, treatment with a PRODH2 inhibitor effectively disrupted the bone metastatic cascade. Together, these results reveal that collagen degradation from osteolysis produces Hyp that reinforces osteoclast differentiation and metastasis, creating a vicious cycle. Identification of the role of the PRODH2–SLC7A11–IL8 axis in promoting breast cancer bone metastasis suggests potential therapeutic strategies to improve patient outcomes. Significance: In the bone microenvironment, osteolysis increases PRODH2-mediated hydroxyproline metabolism that drives osteoclast differentiation and suppresses breast cancer cell ferroptosis, which can be reversed by targeting PRODH2 to suppress metastatic progression.