Is the protection of photosynthesis related to the mechanism of quinclorac resistance in Echinochloa crus-galli var. zelayensis?

Abstract

Echinochloa crus-galli var. zelayensis, a variety of E. crus-galli (L.) Beauv. has evolved resistance to quinclorac, but the mechanism of resistance remains unclear. Treatments with quinclorac, cause rapid leaf chlorosis, continuous decrease in the chlorophyll content to about 0.4 times, and rapid decline in biomass by about 20% in sensitive E. crus-galli var. zelayensis within 72 h. Then transcriptome sequencing for quinclorac-sensitive and -resistant E. crus-galli var. zelayensis biotypes was performed, and more differentially expressed genes (DEGs) were observed in the sensitive biotype (1115 DEGs, including 548 up-regulated and 567 down-regulated) than that in the resistant biotype (901 DEGs, including 373 up-regulated and 528 down-regulated). Thirty-four photosynthesis-related candidate genes were screened, in which twenty-nine genes were more affected by quinclorac in the sensitive biotype than that in the resistant biotype. The qPCR verification involving more sampling time-points revealed that on continuous treatment with 50 μ mol/L quinclorac, expression levels of 34 photosynthesis-related genes dropped significantly by 2–1000 times within 12 h in the sensitive biotype. Following significant or marginal decline in expression at 6 h after quinclorac treatment, recovery of the expression levels of 21 genes was observed after 12 h and the expression levels of another 13 genes remained unaltered in the resistant biotype. It is hypothesized that the sustained sharp decrease in the expression of photosynthesis-related genes is a major cause of death in the sensitive biotype. Further, it is inferred that there may be a regulatory mechanism in the resistant biotype that allowed the expression of these genes to be significantly unaffected or to rapidly recover, in turn preventing severe damage to the plants caused by quinclorac.