CsANU10 maintains chloroplast structural integrity and transcriptional resilience during heat stress in cucumber.

Heat stress destabilizes chloroplast function and frequently leads to leaf chlorosis in crops, yet the genetic mechanisms linking chloroplast integrity to nuclear stress responses remain poorly defined. Here, we identify CsANU10, encoding a chloroplast-localized homolog of Arabidopsis ANGULATA10, as a key regulator of thermosensitive chloroplast stability in cucumber. A recessive missense mutation in CsANU10 causes temperature-dependent and largely irreversible chlorosis accompanied by enlarged and structurally disorganized chloroplasts. Under heat stress, CsANU10 deficiency accelerates chlorophyll loss, impairs photosystem II photochemical efficiency, enhances reactive oxygen species accumulation, and promotes abnormal starch overaccumulation. Transcriptome profiling reveals coordinated repression of heat-inducible chaperone pathways, RNA polymerase II-associated transcriptional programs, and photosynthesis-related genes in the mutant, indicating compromised transcriptional resilience. Together, our findings establish CsANU10 as a critical determinant of chloroplast homeostasis during heat stress and uncover a mechanistic link between chloroplast structural integrity and nuclear transcriptional robustness in a major crop species.