ABSTRACT: SA0420 is a stable rice (Oryza sativa L.) mutant exhibits multiple traits including a leaf-tip yellowing (YLT), a taro fragrance (or aroma, A), a reduced panicle number (PN), spikelet number (SN), plant height (PH), days to heading (DH), filled grain weight (FGW), and fertility rate (FR), different from those of a local cultivar TNG67. Correlation analysis on F2 progenies of SA0420 and TNG67 revealed that except for aroma which is inheritated independently, phenotypes including YLT, PN, SN, PH, and FGW are tightly associated with each others, indicating a control simultaneously by pleotropic gene. Among those phenotypes, YLT appears the earliest at vegetative stage, therefore may act as a predisposing factor that give rise to other phenotypes. Genetic analysis suggested that YLT is controlled by a single recessive gene. By analyzing the recombinant inbreed lines (RILs) that produce YLT and normal green (G) progenies in a 1:3 ratio, the phenotypes associated with YLT were further confirmed. To investigate the molecular events of leaf-tip yellowing, microarray analyses were performed to compare the gene expression profiles between YLT and G plants of RILs. Clustering of genes according to their involved metabolic pathways revealed that various photosynthesis and carbon fixation gene expressions are lower (~55~75%) in YLT than in G plants, consistent with the observation that photosynthesis rate of SA0420 was only 60% to that of TNG67. Moreover, higher expressions of oxidative phosphorylation-related genes indicated that not only the reduced synthesis rate but also the elevated energy consumptions may synergistically decrease the growth vigor of SA0420. Dissection of the mature leaf revealed that chlorophyll is drastically reduced in the leaf-tip of SA0420 while carotenoids remain stable. This explains the appearance of leaf-tip yellowing and recall an analogy of early senescence. Indeed, many senescence-associated genes (SAG) were found to be up-regulated in SA0420. Experiment Overall Design: To investigate the molecular events of leaf-tip yellowing, microarray analyses were performed to compare the gene expression profiles between YLT and G plants of RILs.
