Abstract
The pentatricopeptide repeat (PPR) gene family represents one of the largest gene families in higher plants. Accumulating data suggest that PPR proteins play a central and broad role in modulating the expression of organellar genes in plants. Here we report a rice (Oryza sativa) mutant named young seedling albino (ysa) derived from the rice thermo/photoperiod-sensitive genic male-sterile line Pei'ai64S, which is a leading male-sterile line for commercial two-line hybrid rice production. The ysa mutant develops albino leaves before the three-leaf stage, but the mutant gradually turns green and recovers to normal green at the six-leaf stage. Further investigation showed that the change in leaf color in ysa mutant is associated with changes in chlorophyll content and chloroplast development. Map-based cloning revealed that YSA encodes a PPR protein with 16 tandem PPR motifs. YSA is highly expressed in young leaves and stems, and its expression level is regulated by light. We showed that the ysa mutation has no apparent negative effects on several important agronomic traits, such as fertility, stigma extrusion rate, selfed seed-setting rate, hybrid seed-setting rate, and yield heterosis under normal growth conditions. We further demonstrated that ysa can be used as an early marker for efficient identification and elimination of false hybrids in commercial hybrid rice production, resulting in yield increases by up to approximately 537 kg ha(-1).
Highlights
The pentatricopeptide repeat (PPR) gene family represents one of the largest gene families in higher plants
One of the largest and perhaps the most mysterious gene families uncovered by bioinformatic analyses is the pentatricopeptide repeat (PPR) protein family, which is characterized by the tandem array of a PPR motif, a highly degenerate unit consisting of 35 canonical amino acid
The contents of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid in ysa plants before the three-leaf stage were drastically lower than those in the parental Pei’ai64S plants (Fig. 1D). The levels of these pigments in the ysa mutant increased and became similar to Pei’ai64S plants (Fig. 1E). These results suggest that the albino phenotype of the young ysa seedlings is caused by a reduction in total chlorophyll content, rather than reduction of a particular pigment
Summary
The pentatricopeptide repeat (PPR) gene family represents one of the largest gene families in higher plants. The PPR motif is predicted to resemble the structure of the tetratricopeptide repeat motif that consists of a protein sequence constituting two antiparallel a-helices This motif is found in a few animal and fungal proteins but the family has expanded greatly in higher plants, with 466 members in Arabidopsis and 480 in rice (Small and Peeters, 2000; Lurin et al, 2004). The T/PGMS lines are male sterile under high-temperature and long-day conditions, but they become fertile under lower-temperature and short-day conditions—these conditions are used for the propagation and maintenance of T/PGMS lines This means that a significant fall in temperature during the male-sterility-inductive period could cause the male-sterile lines to become partially fertile, resulting in contamination of the hybrid seeds by T/PGMS selfed seeds and, as a consequence, a decrease in hybrid yield (Bi et al, 1990)
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