The Rice Floral Repressor Early flowering1 Affects Spikelet Fertility By Modulating Gibberellin Signaling

Abstract

BackgroundGibberellic 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.ResultsUsing 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-015-0058-1) contains supplementary material, which is available to authorized users.

Genetic Architecture of Flowering Phenology in Cereals and Opportunities for Crop Improvement

“…Flowering time genes and regulators often have pleiotropic effects on multiple agronomically important traits, including the number and size of seeds, spikelet fertility, growth vigor, and stress tolerance (Xue et al, 2008; Ni et al, 2009; Andres and Coupland, 2012; Kwon et al, 2015). A major driver of crop evolution and adaptation, flowering time genes are key selection factors for crop breeding.…”

Regulatory Networks in Pollen Development under Cold Stress

“…Gibberellic acid is a relatively well-studied growth regulator for its role in anther and pollen development. GAs are vital to anther development as well as pollen viability ( Kwon et al, 2015 ), and GA signaling predominantly works in tapetal cells ( Plackett et al, 2011 ). GA regulates tapetum differentiation as well as initiation of tapetum programmed cell death (PCD) via GA-regulated myeloblastosis (GAMYB), a gibberellin-regulated transcriptional activator ( Plackett et al, 2014 ).…”

“…A casein kinase I (CK1) protein called Rice early flowering1 (EL1) phosphorylates DELLA protein SLR1 (slender rice 1) in rice to negatively regulate gibberellin signaling ( Dai and Xue, 2010 ). Recent evidence suggests that the modulation of GA activity by EL1 is essential for anther development and pollen viability as el1 mutants were early flowering but with low fertility ( Kwon et al, 2015 ). GAMYB appears to be the key TF in GA signaling pathway.…”

GENETIC DIVERSITY AND TRAIT ASSOCIATION ANALYSIS OF INDONESIAN RICE (Oryza sativa L.) GERMPLASM USING SSR MARKERS

“…Gando, Padi Dewi, Talun Bajang and Ringkak Siman). Kwon et al (2015) found that a deficiency of SLR1 activity causes different spikelet fertility phenotypes in two different cultivars, Koshihikari and H143 which H143 exhibits partial sterility of spikelets while Koshihikari has normal fertility. Liu et al (2013) mentioned that spikelet fertility is a critical yield-determining trait that is influenced by genetic background and environmental factors including rain, wind, and temperature.…”