MicroRNA directs mRNA cleavage of the transcription factor NAC1 to downregulate auxin signals for arabidopsis lateral root development

Although several plant microRNAs (miRNAs) have been shown to play a role in plant development, no phenotype has yet been associated with a reduction or loss of expression of any plant miRNA. Arabidopsis thaliana miR164 was predicted to target five NAM/ATAF/CUC (NAC) domain-encoding mRNAs, including NAC1, which transduces auxin signals for lateral root emergence. Here, we show that miR164 guides the cleavage of endogenous and transgenic NAC1 mRNA, producing 3'-specific fragments. Cleavage was blocked by NAC1 mutations that disrupt base pairing with miR164. Compared with wild-type plants, Arabidopsis mir164a and mir164b mutant plants expressed less miR164 and more NAC1 mRNA and produced more lateral roots. These mutant phenotypes can be complemented by expression of the appropriate MIR164a and MIR164b genomic sequences. By contrast, inducible expression of miR164 in wild-type plants led to decreased NAC1 mRNA levels and reduced lateral root emergence. Auxin induction of miR164 was mirrored by an increase in the NAC1 mRNA 3' fragment, which was not observed in the auxin-insensitive mutants auxin resistant1 (axr1-12), axr2-1, and transport inhibitor response1. Moreover, the cleavage-resistant form of NAC1 mRNA was unaffected by auxin treatment. Our results indicate that auxin induction of miR164 provides a homeostatic mechanism to clear NAC1 mRNA to downregulate auxin signals.     

Arabidopsis fatty acid desaturase FAD2 is required for salt tolerance during seed germination and early seedling growth

Fatty acid desaturases play important role in plant responses to abiotic stresses. However, their exact function in plant resistance to salt stress is unknown. In this work, we provide the evidence that FAD2, an endoplasmic reticulum localized ω-6 desaturase, is required for salt tolerance in Arabidopsis. Using vacuolar and plasma membrane vesicles prepared from the leaves of wild-type (Col-0) and the loss-of-function Arabidopsis mutant, fad2, which lacks the functional FAD2, we examined the fatty acid composition and Na+-dependent H+ movements of the isolated vesicles. We observed that, when compared to Col-0, the level of vacuolar and plasma membrane polyunsaturation was lower, and the Na+/H+ exchange activity was reduced in vacuolar and plasma membrane vesicles isolated from fad2 mutant. Consistent with the reduced Na+/H+ exchange activity, fad2 accumulated more Na+ in the cytoplasm of root cells, and was more sensitive to salt stress during seed germination and early seedling growth, as indicated by CoroNa-Green staining, net Na+ efflux and salt tolerance analyses. Our results suggest that FAD2 mediated high-level vacuolar and plasma membrane fatty acid desaturation is essential for the proper function of membrane attached Na+/H+ exchangers, and thereby to maintain a low cytosolic Na+ concentration for salt tolerance during seed germination and early seedling growth in Arabidopsis.     

生长素调控种子的休眠与萌发

植物种子的休眠与萌发,是植物生长发育过程中的关键阶段,也是生命科学领域的研究热点。种子从休眠向萌发的转换是极为复杂的生物学过程,由外界环境因子、体内激素含量及信号传导和若干关键基因协同调控。大量研究表明,植物激素脱落酸(Abscisic acid, ABA)和赤霉素(Gibberellin acid, GA)是调控种子休眠水平,决定种子从休眠转向萌发的主要内源因子。ABA与GA在含量和信号传导两个层次上的精确平衡,确保了植物种子能以休眠状态在逆境中存活,并在适宜的时间启动萌发程序。生长素(Auxin)是经典植物激素之一,其对向性生长和组织分化等生物学过程的调控已有大量研究。但最近有研究证实,生长素对种子休眠有正向调控作用,这表明生长素是继ABA之后的第二个促进种子休眠的植物激素。本文在回顾生长素的发现历程、阐释生长素体内合成途径及信号传导通路的基础上,重点综述了生长素通过与ABA的协同作用调控种子休眠的分子机制,并对未来的研究热点进行了讨论和展望。