Maize Response to Weeds When Present through Part or All of the Critical Weed Free Period.

Maize responds to weed pressure with significantly reduced yield if weeds were present during the critical weed free period (CWFP). Previous studies indicated that weeds presence during the CWFP could reduce yields even when the weeds were physically separated from the maize and were not competing with the weeds for resources. Thus, it appears that weed presence during the CWFP signals a developmental response in the maize that is carried through the remainder of the growing season - even if the weeds were subsequently removed during the CWFP. To examine the responses of maize to weed presence during all or part of the CWFP, we used RNAseq to compare the transcriptome of weed-free control plants harvested at V8 (the end of the CWFP) to plant in which the weeds were present through all (to V8) or only part of the CWFP (through V4). As expected, fewer genes were differentially expressed relative to the control when maize plants were allowed to recover from direct weed pressure than when weeds were present through the entire CWFP. When weeds were present at harvest, significant reduction in photosynthesis, protein and amino-acid production, oxidative stress responses, and growth were noted. Likewise, weed presence through V8 induced multiple biotic and abiotic stress responses -often involving jasmonic and abscisic acid responses, and flavonoid and anthocyanin biosynthetic processes. However, if weeds were removed at V4, reduced expression of genes involved in protein synthesis and oxidative stress responses were observed as were induction of multiple biotic and abiotic stress responses, and flavonoid and anthocyanin biosynthetic processes. Interestingly, the reduction in photosynthesis genes was not evident if the weeds were not present. These data suggest that general stress responses are induced by weeds, and that this induction is maintained even if the weeds are removed during the CWFP.