| Aldehyde dehydrogenase (ALDH) represents a superfamily of NAD(P)+-dependent enzymes that oxidize aldehydes into their corresponding carboxylic acids. ALDH comprises at least22families according to protein sequence identity, and plays derivate functions based on their substrates. In plant, twelve families were present and a few of them are studied in detail comparing the research in human.Most of the studies of plant ALDH genes were just restricted to the expression patterns. The family ALDH7is highly conserved in whatever animals or plants. ALDH7A1, ALDH7homolog in human, catalyzes the oxidation of α-amino adipic semialdehyde (AASA) in lysine degradation. As yet, the expressions of ALDH7in plants such as garden pea, brassica, apple, tortula ruralis, sorghum and Arabidopsis were found to be associated with seed maturation and osmotic stress, but their exact functions were still remain to be clarified. Recently, ALDH7in rice was found to play a role during seed storage, resulted in an unidentified yellow pigment accumulation of the mutant endosperm, which are probably products of maillard reaction. On the other hand, a new kind of pigment compounds called oryzamutaic acids were detected in var. Hatsuyamabuki. However, no information is yet available for our understanding the production of oryzamutaic acids. In this study, using a natural mutant of yellow endosperm,OsALDH7, the gene responsible for the phenotype, was cloned. Besides its expression pattern, the possible role of OsALDH7in lysine degradation was further investigated. The main conclusions are as follows:1. A natural mutant of yellow endosperm was identified from a low-glutelin var. W3660, which named as jmw (new golden rice in Chinese) contrast to the artificial produced golden rice. The mutant was identical to the wildtype except for the color and the protein content in endosperm. Yellow pigments could be soluble in water but not in organic solvents. Genetic analysis showed that the yellow endosperm caused by one pair of recessive nuclear gene mutation. Using a F2group, the mutated gene was mapped to an interval of～26-kb on Chromosome9, which included six putative genes.2. After sequencing and comparing the intervals between W3660and jmw, a mutant in the exon10of the putative gene LOC_Os09g26880, named OsALDH7, was detected. Complement experiment indicated that OsALDH7was the correct gene responsible for the production of yellow pigment. The expression of OsALDH7in rice may be induced under the treatments of dehydration, salinity and ABA especially in leaf, and the drought resisting was weaker in the mutant, indicating OsALDH7plays an important role in the plant defense to the osmotic stresses. Some ALDH genes express much higher in the mutant than the wild type, indicating the possible compensating pattern in ALDH family.3. The main pigment in our mutant was confirmed as oryzamutaic acid A, and the contents of oryzamutaic acid A in W3660and jmw were detected by high performance liquid chromatography (HPLC), which could confirm the conclusion. The pigment accumulation was more obvious along with seed ripen or aging, which is consistent with to the phenotype. Comparing the ALDH7function in human, its probable role on lysine catabolism was also investigated. The expression of related gene{LOR/SDH, AK, DHPS) and the contents of intermediate compounds (saccharopine) in lysine metabolism were detected in W3660and jmw. The mutation of OsALDH7induced the accumulation of saccharopine but the degradation of lysine. Moreover, the over-expressing of OsALDH7in yeast could cause great decease of lysine and an increase of glutamate, which is the product of lysine degradation. OsALDH7in rice probably participate in the degradation of lysine, and without OsALDH7, lysine might be transformed to the pigment like oryzamutaic acid A through some unknown processes... |
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