The <i>ABI4</i>-Induced Arabidopsis <i>ANAC060</i> Transcription Factor Attenuates ABA Signaling and Renders Seedlings Sugar Insensitive when Present in the Nucleus

<div><p>Seedling establishment is inhibited on media containing high levels (∼6%) of glucose or fructose. Genetic loci that overcome the inhibition of seedling growth on high sugar have been identified using natural variation analysis and mutant selection, providing insight into sugar signaling pathways. In this study, a quantitative trait locus (QTL) analysis was performed for seedling sensitivity to high sugar in a Col/C24 F₂ population of <i>Arabidopsis thaliana</i>. A glucose and fructose-sensing QTL, <i>GSQ11</i>, was mapped through selective genotyping and confirmed in near-isogenic lines in both Col and C24 backgrounds. Allelism tests and transgenic complementation showed that <i>GSQ11</i> lies within the <i>ANAC060</i> gene. The Col <i>ANAC060</i> allele confers sugar insensitivity and was dominant over the sugar-sensitive C24 allele. Genomic and mRNA analyses showed that a single-nucleotide polymorphism (SNP) in Col <i>ANAC060</i> affects the splicing patterns of <i>ANAC060</i> such that 20 additional nucleotides are present in the mRNA. The insertion created a stop codon, resulting in a truncated ANAC60 protein lacking the transmembrane domain (TMD) that is present in the C24 ANAC060 protein. The absence of the TMD results in the nuclear localization of ANAC060. The short version of the ANAC060 protein is found in ∼12% of natural Arabidopsis accessions. Glucose induces <i>GSQ11/ANAC060</i> expression in a process that requires abscisic acid (ABA) signaling. Chromatin immunoprecipitation-qPCR and transient expression analysis showed that ABI4 directly binds to the <i>GSQ11/ANAC060</i> promoter to activate transcription. Interestingly, Col <i>ANAC060</i> reduced ABA sensitivity and Glc-induced ABA accumulation, and <i>ABI4</i> expression was also reduced in Col <i>ANAC060</i> lines. Thus, the sugar-ABA signaling cascade induces <i>ANAC060</i> expression, but the truncated Col ANAC060 protein attenuates ABA induction and ABA signaling. This negative feedback from nuclear ANAC060 on ABA signaling results in sugar insensitivity.</p>