Abstract
Leaf-color is an effective marker to identify the hybridization of rice. Leaf-color related genes function in chloroplast development and the photosynthetic pigment biosynthesis of higher plants. The ygl7 (yellow-green leaf 7) is a mutant with spontaneous yellow-green leaf phenotype across the whole lifespan but with no change to its yield traits. We cloned gene Ygl7 (Os03g59640) which encodes a magnesium-chelatase ChlD protein. Expression of ygl7 turns green-leaves to yellow, whereas RNAi-mediated silence of Ygl7 causes a lethal phenotype of the transgenic plants. This indicates the importance of the gene for rice plant. On the other hand, it corroborates that ygl7 is a non-null mutants. The content of photosynthetic pigment is lower in Ygl7 than the wild type, but its light efficiency was comparatively high. All these results indicated that the mutational YGL7 protein does not cause a complete loss of original function but instead acts as a new protein performing a new function. This new function partially includes its preceding function and possesses an additional feature to promote photosynthesis. Chl1, Ygl98, and Ygl3 are three alleles of the OsChlD gene that have been documented previously. However, mutational sites of OsChlD mutant gene and their encoded protein products were different in the three mutants. The three mutants have suppressed grain output. In our experiment, plant materials of three mutants (ygl7, chl1, and ygl98) all exhibited mutational leaf-color during the whole growth period. This result was somewhat different from previous studies. We used ygl7 as female crossed with chl1 and ygl98, respectively. Both the F1 and F2 generation display yellow-green leaf phenotype with their chlorophyll and carotenoid content falling between the values of their parents. Moreover, we noted an important phenomenon: ygl7-NIL's leaf-color is yellow, not yellowy-green, and this is also true of all back-crossed offspring with ygl7.
Highlights
Genetic purity of crop plants, which has a critical impact on increasing crop yields, is gradually becoming the focus in hybrid rice production [1]
Study of the genetic mechanism of leaf-color mutations would further our understanding of chlorophyll biosynthesis and degradation, chloroplast development, tetrapyrrole synthesis, and photosynthesis
Compared to same combinations which crossed with 810S, there were no significant differences in main agronomic traits, including the growth period, maturing rate, and 1000-grain weight (Table 2). These results suggested that this phenotype does not influence grain output and hybrid characteristics
Summary
Genetic purity of crop plants, which has a critical impact on increasing crop yields, is gradually becoming the focus in hybrid rice production [1]. Plants with a distinct color phenotype can be identified and removed, so leaf-color has become a suitable marker for maintaining the genetic purity of hybrid rice [2]. As of 2013, at least 208 leaf-color mutants have been identified in rice. Only 53 leaf-color genes of rice have been cloned (14 of them had alleles). 14 genes function directly in chlorophyll biosynthesis and catabolism (DCBC) [4,5,6,7,8,9,10,11], while 6 genes indirectly take part in those two processes (ICBC) [12,13,14,15]. Three genes influence rice leaf-color via other pathways (OP) [27].
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