Abstract
Plant root system architecture in response to nitrate availability represents a notable example to study developmental plasticity, but the underlying mechanism remains largely unknown. Xyloglucan endotransglucosylases (XTHs) play a critical role in cell wall biosynthesis. Here we assessed the gene expression of XTH1-11 belonging to group I of XTHs in lateral root (LR) primordia and found that XTH9 was highly expressed. Correspondingly, an xth9 mutant displayed less LR, while overexpressing XTH9 presented more LR, suggesting the potential function of XTH9 in controlling LR development. XTH9 gene mutation obviously alters the properties of the cell wall. Furthermore, nitrogen signals stimulated the expression of XTH9 to promote LRs. Genetic analysis revealed that the function of XTH9 was dependent on auxin-mediated ARF7/19 and downstream AFB3 in response to nitrogen signals. In addition, we identified another transcription factor, OBP4, that was also induced by nitrogen treatment, but the induction was much slower than that of XTH9. In contrast to XTH9, overexpressing OBP4 caused fewer LRs while OBP4 knockdown with OBP4-RNAi or an artificial miRNA silenced amiOBP4 line produced more LR. We further found OBP4 bound to the promoter of XTH9 to suppress XTH9 expression. In agreement with this, both OBP4-RNAi and crossed OBP4-RNAi & 35S::XTH9 lines led to more LR, but OBP4-RNAi & xth9 produced less LR, similar to xth9. Based on these findings we propose a novel mechanism by which OBP4 antagonistically controls XTH9 expression and the OBP4-XTH9 module elaborately sustains LR development in response to nitrate treatment.
Highlights
In the biosphere, nitrate is the major form of nitrogen, and nitrate availability is important for plant development
Changes in root system architecture in response to nitrate availability represent a notable example of developmental plasticity in response to environmental stimuli
Previous genomic studies have shown that the nitrate response is comprehensive, but the molecular mechanisms of nitrate signal transduction and the downstream gene expression changes that lead to developmental responses, such as changes in root system architecture (RSA), are still unclear
Summary
Nitrate is the major form of nitrogen, and nitrate availability is important for plant development. Nitrate is a nutrient, and a signal that controls downstream signaling genes at the whole-plant level [1, 2]. The MADS family NO3−-inducible transcription factor (TF) ANR1 and Lateral Organ Boundaries Domain (LBD) regulate lateral root (LR) growth in response to nitrate treatment [8, 9]. NIN-like protein 7 (NLP7) orchestrates the early response to nitrate in plants [10], and via a systems biology approach, TGACG SEQUENCE -SPECIFIC BINDING PROTEIN 1(TGA1), AUXIN SIGNALING F-BOX 3 (AFB3), ARABIDOPSIS NAC DOMAIN-CONTAINING PROTEIN 79 (NAC4), and OBP4 genes have been identified as nitrate regulators involved in nitrate signaling [2,11,12]
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