Morphological and gene expression analysis under cool temperature conditions in rice anther development

Abstract

Cool temperature conditions are known to lead to pollen sterility in rice. Pollen sterility is an agriculturally important phenomenon because it imparts a large influence directly on rice yield. However, cool temperature stress tolerance varies among rice cultivars and avoidance of cool temperature stress is difficult by practical method of agriculture. In this study using two rice cultivars, Hitomebore (high tolerance) and Sasanishiki (low tolerance), we analyzed morphological features and gene expression profiles, under cool temperature stress, in anther development of rice. Hitomebore was given cool temperature stress (19°C) at flowering stage, and showed 87.3% seed fertility. Meanwhile, the seed fertility decreased to 41.7% in the case of Sasanishiki. A transverse section of Hitomebore anther revealed that the degradation of the tapetum started at the uninucleate microspore stage, and the tapetum had completely vanished at mature stage. The tapetum provides nutrients for pollen development, and its degradation occurs at a late stage in pollen development. In contrast, degradation of the tapetum did not occur at the uninucleate microspore stage in Sasanishiki, and the tapetum was clearly intact at mature stage, suggesting that tapetum degradation is critical for accurate pollen development and cool temperature tolerance correlated with the degree of tapetum degeneration. In gene expression analysis of anther, 356 genes that showed different expression levels between two cultivars at cool temperatures were found. These genes will lead to understanding the mechanism of cool temperature stress response in rice pollen development and the identification of genes involved in accurate tapetum degradation.

Reduction of Gibberellin by Low Temperature Disrupts Pollen Development in Rice

“…Although stress tolerance response pathways mediated by GA are complex, it is well known that GA-deficient and GA-insensitive mutants in several plant species display abnormal anther development (Nester and Zeevaart, 1988;Jacobsen and Olszewski, 1991;Cheng et al, 2004;Aya et al, 2009). The typical defect of abnormal tapetal cell enlargement observed in rice GA mutants (Aya et al, 2009) is quite similar to the observed effects induced by LT injury in wild-type cultivated rice plants (Nishiyama, 1976;Oda et al, 2010).…”

“…This resembles the effects induced by cool-temperature damage in cultivated rice plants (Nishiyama, 1976;Oda et al, 2010). Therefore, we measured alterations in the levels of endogenous GAs in developing anthers of the japonica cv Sasanishiki grown under normal and LT (average 19°C) conditions in a field at Furukawa Agricultural Experiment Station, Miyagi Prefecture, Japan (see "Materials and Methods"; Supplemental Fig.…”

“…2). As the decline in GA 1 content was matched with an accumulation of GA 20 under both normal and LT conditions, GA3b-hydroxylase1 (GA3ox1), which was dominantly expressed in developing anthers (Oda et al, 2010), could more efficiently convert GA 9 to GA 4 than GA 20 to GA 1 . GA 3 , GA 8 , GA 19 , GA 44 , and GA 53 were hardly detected in anthers under normal conditions.…”

“…We monitored the transcription of the GA biosynthesis genes GA3ox1 and GA20ox3 (expressed dominantly in anthers; Oda et al, 2010) during pollen development at the premeiotic, meiotic, uninucleate, binucleate, and trinucleate stages. The expression of GA20ox3 was significantly up-regulated at the binucleate pollen stage in the control (Fig.…”

“…S2). The other GA2oxs are barely expressed in developing anthers of rice (Oda et al, 2010; http://ricexpro.dna.affrc.go.jp/). Taken together, these results indicate that LT severely reduces the endogenous levels of bioactive GAs through transcriptional repression of the GA biosynthetic genes GA20ox3 and GA3ox1, which are strongly up-regulated during normal anther development.…”