The Effect of the Crosstalk between Photoperiod and Temperature on the Heading-Date in Rice

Photoperiod and temperature are two important environmental factors that influence the heading-date of rice. Although the influence of the photoperiod on heading has been extensively reported in rice, the molecular mechanism for the temperature control of heading remains unknown. This study reports an early heading mutant derived from tissue culture lines of rice and investigates the heading-date of wild type and mutant in different photoperiod and temperature treatments. The linkage analysis showed that the mutant phenotype cosegregated with the Hd1 locus. Sequencing analysis found that the mutant contained two insertions and several single-base substitutions that caused a dramatic reduction in Hd1mRNA levels compared with wild type. The expression patterns of Hd1 and Hd3a were also analyzed in different photoperiod and temperature conditions, revealing that Hd1 mRNA levels displayed similar expression patterns for different photoperiod and temperature treatments, with high expression levels at night and reduced levels in the daytime. In addition, Hd1 displayed a slightly higher expression level under long-day and low temperature conditions. Hd3a mRNA was present at a very low level under low temperature conditions regardless of the day-length. This result suggests that suppression of Hd3a expression is a principle cause of late heading under low temperature and long-day conditions

OsNAC103, a NAC Transcription Factor, Positively Regulates Leaf Senescence and Plant Architecture in Rice

Abstract Leaf senescence, the last stage of leaf development, is essential for crop yield by promoting nutrition relocation from senescence leaves to new leaves and seeds. NAC (NAM/ATAF1/ATAF2/CUC2) proteins, one of the plant-specific transcription factors, widely distribute in plants and play important roles in plant growth and development. Here, we identified a new NAC member OsNAC103 and found that it plays critical roles in leaf senescence and plant architecture in rice. OsNAC103 mRNA levels were dramatically induced by leaf senescence as well as different phytohormones such as ABA, MeJA and ACC and abiotic stresses including dark, drought and high salinity. OsNAC103 acts as a transcription factor with nuclear localization signals at the N terminal and a transcriptional activation signal at the C terminal. Overexpression of OsNAC103 promoted leaf senescence while osnac103 mutants delayed leaf senescence under natural condition and dark-induced condition, meanwhile, senescence-associated genes (SAGs) were up-regulated in OsNAC103 overexpression (OsNAC103-OE) lines, indicating that OsNAC103 positively regulates leaf senescence in rice. Moreover, OsNAC103-OE lines exhibited loose plant architecture with larger tiller angles while tiller angles of osnac103 mutants decreased during the vegetative and reproductive growth stages due to the response of shoot gravitropism, suggesting that OsNAC103 can regulate the plant architecture in rice. Taken together, our results reveal that OsNAC103 plays crucial roles in the regulation of leaf senescence and plant architecture in rice

Sequence analysis of <i>Hd1</i> in <i>lf1132</i> and wild type.

<p>A: The sequence differences between wild type and <i>lf1132</i>. The black triangle represents insertion; vertical lines represent single-base substitutions; blue vertical lines and numbers are relative positions in <i>hd1-3</i>. SEF and SER shown by arrows are primers to detect the 315 bp insertion. B: PCR detection of the 315 bp insertion on the <i>hd1-3</i> locus for <i>lf1132</i>. C: The expression of <i>Hd1</i> in the wild type and mutant. Leaves were harvested from 30 day old seedlings at the indicated times (once every 3 h for 24 h) in natural fields (day-length is about 14 h light and 10 h dark) and RT-PCR was carried out for the analysis of <i>Hd1</i> expression. Primer pairs HD1F and HD1R were used for the analysis of <i>Hd1</i> expression in RT-PCR. D: Deduced amino acid sequence of the Hd1 and deduced lf1132 proteins. The black line indicates the zinc-finger domain; asterisks are amino acid substitutions between the Nipponbare Hd1 protein and the deduced lf1132 protein. E: the linkage analysis of the mutant and <i>Hd1</i> locus. P₁ is Zhonghua 11; P₂ is <i>lf1132</i>.</p

The phenotype of the mutant.

<p>A: the phenotype of the mutant and wild type, M is mutant <i>lf1132</i>; WT is Zhonghua 11. B: the panicle length and internode length for mutants and wild type. 15 total plants were investigated from five repeats containing three individuals. C: The heading-date of the wild type and mutant on different sowing-dates. Wild type and mutant were planted in the CNRRI experimental field, Zhejiang province on six sowing-dates from 15, May to 21, July 2007. D: The change in photoperiod during different sowing-dates. E: The change in temperature (mean value of everyday temperature) during different sowing-dates. Red box indicates the temperature of the heading period at the last sowing-date, 21, July.</p

The heading-date of the mutant and wild type for different photoperiod and temperature treatments.

<p><i>lf1132</i> and wild type plants were planted in the CNRRI experimental fields, and two week old seedlings were transferred to phytotrons with different photoperiod and temperature treatments. The heading-date for each treatment was observed and recorded for at least 10 plants. Four phytotrons were used: LD, 27°C phytotron; LD, 23°C phytotron; SD, 27°C phytotron; SD, 23°C phytotron; A: the heading-date under different photoperiods and temperatures; B: The velocity ratio of leaf growth (VRL) for the mutant and wild type under different photoperiods (SD and LD) and temperatures (27°C, 23°C). LD treatment: 14.5 h light and 9.5 h dark; SD treatment: 11.5 h light and 12.5 h dark.</p

<i>Hd3a</i> expression under different photoperiods and temperatures.

<p>Leaves were harvested from 33 day old plants at the indicated times (once every 4 h for 24 h) in phytotrons, and real-time PCR was carried out for the analysis of <i>Hd3a</i> expression. M is <i>lf1132</i>; WT is Zhonghua 11. A, B, C, D are the <i>Hd3a</i> expression profiles under high temperature and low temperature; A: wild type under LD condition; B: wild type under SD condition; C: mutant under LD condition; D: mutant under SD condition. E and F are the <i>Hd3a</i> expression profiles for the wild type and mutant under different photoperiods at high temperature; E: wild type; F: mutant. G presents the <i>Hd3a</i> expression profile of the mutant and wild type under LD conditions.</p

<i>Hd1</i> expression under different photoperiods and temperatures.

<p>Leaves were harvested from 33 day old plants at the indicated times (once every 4 h for 24 h) in phytotrons, and real-time PCR was carried out for analysis of <i>Hd1</i>. M is <i>lf1132</i>; WT is Zhonghua 11.</p

Leaf number of mutant and wild type in different photoperiod treatments and temperature treatments.

<p>Notes: Zhonghua 11(wild type) and <i>lf1132</i> (mutant) were grown in phytotrons with four different treatments. The main-stem leaf number was investigated at least 10 plants for each treatment in four phytotrons.</p

The effect of different photoperiods and temperatures on heading-date.

<p>Notes: Zhonghua 11 and <i>lf1132</i> were grown in phytotrons with four different treatments. Heading-date was investigated at least 10 plants for each treatment.</p