Regulation of maize growth and immunity by ZmSKI3-mediated RNA decay and post-transcriptional gene silencing

Disease resistance is often associated with compromised plant growth and yield due to defense-growth tradeoffs.However,key components and mechanisms underlying the defensegrowth tradeoffs are rarely explored in maize.In this study,we find that ZmSKI3,a putative subunit of the SUPERKILLER(SKI)complex that mediates the 3′-5′degradation of RNA,regulates both plant development and disease resistance in maize.The Zmski3 mutants showed retarded plant growth and constitutively activated defense responses,while the ZmSKI3 overexpression lines are more susceptible to Curvularia lunata and Bipolaris maydis.Consistently,the expression of defense-related genes was generally up-regulated,while expressions of growth-related genes were mostly down-regulated in leaves of the Zmski3-1 mutant compared to that of wild type.In addition,223 differentially expressed genes that are up-regulated in Zmski3-1 mutant but down-regulated in the ZmSKI3 overexpression line are identified as potential target genes of ZmSKI3.Moreover,small interfering RNAs targeting the transcripts of the defense-and growth-related genes are differentially accumulated,likely to combat the increase of defense-related transcripts but decrease of growthrelated transcripts in Zmski3-1 mutant.Taken together,our study indicates that plant growth and immunity could be regulated by both ZmSKI3-mediated RNA decay and post-transcriptional gene silencing in maize.

Abscisic Acid Antagonizes Ethylene Production through the ABI4-Mediated Transcriptional Repression of ACS4 and ACS8 in Arabidopsis

Increasing evidence has revealed that abscisic acid （ABA） negatively modulates ethylene biosynthesis, although the underlying mechanism remains unclear. To identify the factors involved, we conducted a screen for ABA-insensitive mutants with altered ethylene production in Arabidopsis. A dominant allele of ABI4, abi4-152, which produces a putative protein with a 16-amino-acid truncation at the C-terminus of ABI4, reduces ethylene production. By contrast, two recessive knockout alleles of ABI4, abi4-102 and abi4-103, result in increased ethylene evolution, indicating that ABI4 negatively regulates ethylene produc- tion. Further analyses showed that expression of the ethylene biosynthesis genes ACS4, ACSS, and AC02 was significantly decreased in abi4-152 but increased in the knockout mutants, with partial dependence on ABA. Chromatin immunoprecipitation-quantitative PCR assays showed that ABI4 directly binds the pro- moters of these ethylene biosynthesis genes and that ABA enhances this interaction. A fusion protein containing the truncated ABI4-152 peptide accumulated to higher levels than its full-length counterpart in transgenic plants, suggesting that ABI4 is destabilized by its C terminus. Therefore, our results demon- strate that ABA negatively regulates ethylene production through ABI4-mediated transcriptional repression of the ethylene biosynthesis genes ACS4 and ACS8 in Arabidopsis.