Choon-Tak Kwon¹  , Suk-Hwan Kim¹  , Dami Kim¹   and Nam-Chon Paek^{1, 2}  

RICE Published online: 24 July 2015; http://link.springer.com/article/10.1186/s12284-015-0058-1/fulltext.html

Abstract

Background

Gibberellic acid (GA; or gibberellin) affects the development of floral organs, especially anthers and pollen, and perturbation of development of male floral organs can cause sterility. Many studies of GA signaling have concentrated on anther development, but the effect of GA on grain production remains to be examined.

Results

Using a cross of ‘Milyang23 (M23)’, which has a functional allele of Early flowering1 (EL1), and ‘H143’, which has a nonfunctional el1 allele, we generated heterogeneous inbred family-near isogenic lines (HNILs) that are homozygous for EL1 [HNIL(M23)] or el1 [HNIL(H143)]. Here, we found that HNIL(H143) exhibited anther deformities and low pollen viability. The expression of GAMYB, a major activator of GA signaling, and its downstream genes CYP703A3 and KAR, mainly involved in pollen formation, increased abnormally during spikelet development; this activation of GA signaling may cause the sterility. To confirm the negative effect of the el1 mutation on spikelet fertility, we examined a line carrying a T-DNA insertion el1 mutant [hereafter ZH11(el1)] and its parental cultivar ‘Zhonghua11 (ZH11)’. ZH11(el1) showed nearly identical defects in anther development and pollen viability as HNIL(H143), leading to decreased seed setting rate. However, the elite japonica cultivar Koshihikari, which has a nonfunctional el1 allele for early flowering in long days, produces fertile spikelets and normal grain yields, like other elite japonica cultivars. This indicates that as-yet-unknown regulator(s) that can overcome the male sterile phenotype of the el1 mutation must have been introduced into Koshihikari.

Conclusions

The el1 mutation contributes to early flowering in japonica rice under long days but fails to limit GA signaling, thus negatively affecting spikelet fertility, which results in a loss of grain yield. Thus, EL1 is essential for photoperiod sensitivity in flowering as well as spikelet fertility in grain production.

Fig. 1

HNIL(H143) showed abnormal anther and pollen development compared with HNIL(M23). a Panicle structure of HNIL(M23) and HNIL(H143) plants at the heading stage. Scale bar = 20 mm. b Spikelets of the HNIL(M23) and HNIL(H143) plants. Scale bar = 20 mm (b and c). c Flowers of the HNIL(M23) and HNIL(H143) plants. An, anther; Le, lemma; Fl, filament; Pl, palea. d Anthers of the HNIL(M23) and HNIL(H143) plants. Scale bar = 10 mm. e Pistils of the HNIL(M23) and HNIL(H143) plants. Scale bar = 1 mm. Pollen grains from (f) HNIL(M23) and (g) HNIL(H143) plants. Pollen stained with I₂-KI solution. Scale bar = 200 μm (f and g). The data represent five independent biological replicates