Functional study of Arabidopsis AtNRT1.13
Date Issued
2010
Date
2010
Author(s)
Cheng, Ling-Hsin
Abstract
Nitrate is not only the primary nitrogen source but also a signaling molecule regulating plant development. A study of the uptake- and sensing-decoupled mutant chl1-9 demonstrates that CHL1 (AtNRT1.1) is not only a transporter but also a sensor. Pro492, which is mutated in the chl1-9 mutant, is required for nitrate transport, but not for nitrate sensing. Pro492 was highly conserved among NRT1 (PTR) family of Arabidopsis thaliana, except two members, NRT1.13 and NRT1.14. Pro was substituted by Ser in NRT1.13 and Ala in NRT1.14, respectively. It will be interesting to find out if these two NRT1 transporters are involved in nitrate sensing. Consistently, a rice NRT1 (PTR) transporter SP1 (Short Panicle 1) with the corresponding Pro492 residue substituted by Leu exhibit no nitrate transport activity when expressed in Xenopus oocyte and display a short panicle phenotype when mutated. Indeed, NRT1.13 (At1g33440) is classified into the same subgroup with SP1 (Os11g12740). This suggested NRT1.13 might also participate in regulating plant development.
Histochemical analysis of PNRT1.13-GUS and quantitative PCR analysis showed that NRT1.13 was mainly expressed in parenchyma cell of petiole, spray and distal part of stem. Furthermore, subcellular localization analysis showed that NRT1.13-GFP fusion protein was in plasma membrane. In order to characterize the in vivo function of NRT1.13, several phenotypes between wild type and nrt1.13 mutant was compared. Compared to the flowering time of 20.8 days in wild type, flowering time in nrt1.13 delayed to 22.9 days. And, the number of leaves when bolted increased from 12.4 in wild type to 14.9 in the mutant. The average distance between sliques of nrt1.13 was also decreased from 0.92 of wild type to 0.64 cm, suggesting that similar to rice SP1, NRT1.13 also participate in regulating elongation of inflorescent stem. In addition, the nitrate content and short-term-15N partition of nrt1.13 were monitored to examine if there were any defects of nrt1.13 in nitrogen distribution. It showed a reduced level of the 15N in distal nodes and flowers of nrt1.13. The nitrate content of nrt1.13 cauline leaf was also reduced. Moreover, germination test showed that fresh seeds of nrt1.13 were more dormant than wild type in a nitrate dependent manner, suggesting that seed nitrate content is reduced in nrt1.13. Taken together, these data indicated that NRT1.13 was important for both developmental regulation and nitrate distribution of reproductive tissue.
Subjects
Arabidopsis
Type
thesis
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