| Plant root is a vital organ, which plays important roles in fixing of plant, absorbing and transporting of water or nutrient, even synthesizing and accumulating of nutrients. The gradient of auxin concentrations affects root development, while maintaining the gradient depends on the polar transport. So far it have been reported that there are three gene families involving in auxin polar transport:the auxin influx carrier AUX/LAX (auxin resistant l/like AUX1) family, the auxin efflux carrier PIN (pin-formed) family and ABCB/MDR/PGP (ATP binding cassette B/Multidrug-resistance/p-glycoprotein) family. In Arabidopsis, the PIN family has been widely studied, while PGP and A UX/LAXfamilies are known less. There are five AUX1 similar genes in rice by homology comparison, but little report on their biological function. In this research, we analyzed the rice OsA UX/LAX family gene structure and protein structure by bioinformatics method, constructed the OsAUX/ LAX promoter fusion reporter gene β-glucuronidase(GUS) to recognize OsAUX/LAX family expression patterns, used OsAUX1 mutant and overexpression materials to uncover the biological function of OsAUXl in primary root and root hair development. The main results are summarized as follows:(1) The OsA UX/LAX family was not similarity in gene structure. There were 5-7 exons in OsAUXl,OsAUX2, OsAUX3 and OsAUX4,2 exons in OsAUX5, while 6-7 exons in AtAUX/LAX. Amino acid sequence homology was 70.58%～84.15%, similar to four proteins in Arabidopsis thaliana, suggesting that the gene family was conservative for auxin input.(2) Protein structure of OsAUX/LAX family was predicted and subcellular location was determined. OsA UX/LAX family consists of 9 to 11 transmembrane and they mainly localize to the plasma membrane.(3) Expression pattern of members in OsAUX/LAX family showed their specificity. Similar to AtAUX1, OsAUX1 is constitutive expression in the phloem, stele, lateral root cap, and primary root tip and elongation zone cells. OsAUX1 only expressed in the lateral root primordia and proximal epidermal cells. OsAUX2, OsAUX4 and OsAUXS were conservative evolutionally in comparison with AtLAX2. They showed the same region in primary root, but different in lateral root. In the shoot those 5 genes were all expressed in the stem vascular, in mesophyll cells, glume, pistil and stamen. OsAUX/LAX family was induced by IAA,2,4-D, salt and cadmium stress.(4) osauxl are not resistant to NAA, but resistant to IAA,2,4-D. Under normal culture conditions the primary roots of mutants were 30% longer than those of wild type, while the length of OsAUXl overexpressed lines was 30% shorter than that of wild type. Lateral root density decreased and root hair length became shorter in the mutant. After treated with high concentrations of exogenous auxin and inhibitor for polar transport carrier, osauxl appeared insensitive to IAA,2,4-D and NPA, while OsAUX1 overexpressed lines were sensitive to IAA,2,4-D and NPA. Additionally, the mutants showed less gravitropism.(5) OsAUXl played role in root hair development. IAA and 2,4-D treatment were unable to restore root hairs’length of osauxl to the wild-type’s level, while NAA treatment could make the mutant’s root hair length reach the wild-type’s level. Transgenic rice with OsAUX1pr.OsAUXl:GFP and OsAUXlp::GUS showed the expression of OsAUXl in the developing root hairs.(6) Mutants osauxl are more sensitive to Cd stress. After cadmium treatment primary root of the mutants became shorter, numbers of lateral root dramatically reduced and root hairs hardly developed. Those might resulted from co-regulation by endogenous auxin, cell cycle and ROS under Cd stress.This research provides a new angle of view for the auxin molecular mechanism in the process of rice root development, and set up the base for rice root improvement in theory and practice. |
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