Fig 1.
Effects of elevated ozone on two rice cultivars, Sasanishiki and Habataki.
(A) Changes in grain yield in 2009 and 2010. (B) Changes in the number of primary rachis branches in 2009 and 2010. Values are mean ± SD (n = 20). Error bars indicate SD; n.s., not significant; *P<0.1; **P<0.05 (Student’s t-test). AA, ambient air; O3, elevated ozone; Sasa, Sasanishiki; Haba, Habataki. (C) Typical panicles of Habataki grown under ambient air (left) or elevated ozone (right). Yellow circles indicateidentify each primary rachis branches. Scale bar = 5 cm.
Fig 2.
Genome scans for ozone-induced yield loss and the number of primary rachis branches.
(A, C) QTL likelihood maps for (A) grain yield and (C) the number of primary rachis branches. Genetic maps were produced by composite interval mapping using differences between ambient air and elevated ozone. (B, D) Additive effect of (B) QTLs for grain yield and (D) the number of primary rachis branches. A positive (negative) additive effect in B and D represents an increasing allele from Sasanishiki (Habataki). The vertical dotted lines separate chromosomes 1–12 (labeled at the bottom) progressing left to right along the x-axis.
Fig 3.
A genetic linkage map showing the positions of QTLs for grain yield and for the number of primary rachis branches on rice chromosomes in 2009 and 2010.
The map is adapted from [43]. Genes known to affect grain yield in rice are indicated on the right of each chromosome.
Fig 4.
Effects of the Habataki-type APO1 gene in Habataki and the SHA422-1.1 near-isogenic line.
(A) Graphical genotype of chromosome 6 of SHA422-1.1 (APO1 near-isogenic line) and SHA422-1.3. The thickest arrow represents the open reading frame of APO1; narrower arrows represent other predicted genes. 1.1, SHA422-1.1; 1.3, SHA422-1.3. Modified from [20]. (B, C) Effects of the Habataki-type APO1 gene on (B) grain yield and (C) the number of primary rachis branches. Values are mean ± SD (n = 36). NF, non-filtered air (converted values); O3, elevated ozone. Bars topped by the same letters are not significantly different (Tukey’s HSD test, P<0.05).
Fig 5.
APO1 amino acid sequences in Sasanishiki and Habataki.
Boxes show predicted functional motifs (I, F-box domain; II, Kelch motif). APO1 of Habataki has two amino acid substitutions (Ile39Val in the F-box domain and Arg226Gly near the Kelch motif), and a deletion of three amino acids (Gly309–Gly311) in comparison with Sasanishiki. Sasa, Sasanishiki; Haba, Habataki.
Fig 6.
Relative levels of APO1 transcript in different organs.
(A) APO1 transcript levels in the fourth leaf, young panicle (10 days before heading), root, and an inflorescence meristem (IM; 23 days before heading). (B) Ozone-induced changes in the APO1 transcript level in inflorescence meristems of Sasanishiki (Sasa) and Habataki (Haba). Values are mean ± SD (n = 3). AA, ambient air; O3, elevated ozone. n.s., not significant; **P<0.05 (Student’s t-test, A). Bars topped by the same letters are not significantly different (Tukey’s HSD test, P<0.05, B).
Fig 7.
Ozone-induced changes in endogenous phytohormone levels in Sasanishiki and Habataki.
The levels of (A, D) ABA, (B, E) JA, and (C, F) JA-Ile were measured in (A–C) inflorescence meristems and (D–F) flag leaves. Values are mean ± SD (n = 3). AA, ambient air, O3, elevated ozone; Sasa, Sasanishiki; Haba, Habataki. Bars topped by the same letters are not significantly different (Tukey’s HSD test, P<0.05).
Fig 8.
A hypothetical model of ozone-induced grain yield loss in Habataki.
(A) Panicle formation flow under ambient air condition. The APO1 transcription is the trigger of phase transition from rachis meristems (RM) to primary and secondary branch meristems (PBM and SBM). The transcript level is higher in Habataki than Sasanishiki, this is the reason Habataki is high-yielding cultivar. (B) Ozone enters leaves through stomata and generates ROS, which triggers generation of JAs and ABA in leaves to attenuate leaf damage. ROS signaling suppress the APO1 transcript level directly or indirectly in Habataki. In parallel, phytohormones generated in leaves might be translocated to inflorescence meristems through the phloem. These impacts suppress differentiation of the RM into the PBM and SBM. Consequently, the decrease in primary rachis branch formation reduces grain yield.