Suppression of OsMADS7 in rice endosperm stabilizes amylose content under high temperature stress

Abstract

High temperature significantly alters the amylose content of rice, resulting in mature grains with poor eating quality. However, only few genes and/or quantitative trait loci involved in this process have been isolated and the molecular mechanisms of this effect remain unclear. Here, we describe a floral organ identity gene, OsMADS7, involved in stabilizing rice amylose content at high temperature. OsMADS7 is greatly induced by high temperature at the early filling stage. Constitutive suppression of OsMADS7 stabilizes amylose content under high temperature stress but results in low spikelet fertility. However, rice plants with both stable amylose content at high temperature and normal spikelet fertility can be obtained by specifically suppressing OsMADS7 in endosperm. GBSSI is the major enzyme responsible for amylose biosynthesis. A low filling rate and high expression of GBSSI were detected in OsMADS7 RNAi plants at high temperature, which may be correlated with stabilized amylose content in these transgenic seeds under high temperature. Thus, specific suppression of OsMADS7 in endosperm could improve the stability of rice amylose content at high temperature, and such transgenic materials may be a valuable genetic resource for breeding rice with elite thermal resilience.

Keywords: MADS-box gene; amylose content; grain quality; high temperature; rice; seed development.

Figure 1

OsMADS7 is expressed intermediately in rice endosperm and induced by HT at the milk stage. Transcripts were measured using qRT‐PCR and normalized to the level of the control sample (6 DAP endosperm) using UBQ10 as internal control. (a) Expression pattern of OsMADS7 in different tissues. Endosperm (g) indicates endosperm at the seed germination stage; endosperms (6 and 9) indicate developing endosperm at 6 and 9 DAP at the filling stage; panicle (b and a) indicate panicles before and after flowering, respectively. (b) Expression of OsMADS7 in developing endosperm is induced by HT. Data represent means ± SE, n = 3 biological replicates, 6–10 developing seeds in each replicate. DAP: day after pollination. H and R indicate seeds harvested from HT and RT growth conditions, respectively.

Figure 2

Quality analysis of OsMADS7 RNAi rice lines with constitutive suppression. (a) Expression of OsMADS7 in the endosperm (8 DAP) of RNAi lines and WT plants. (b) Appearance of polished rice of RNAi line M734 and WT. (c) The AC of WT (ZH11) and RNAi line seeds grown at different temperatures. (d) The DD‐value of RNAi lines. The D‐value of WT was set to zero and used as a control. (e, f) Rice Tp and ΔH from WT and M734. Tp: peak transition temperature; ΔH: enthalpies of gelatinization. In (c‐f), data represent means ± SE, n = 3 biological replicates. A significant difference was determined by Student's t‐test, not significant (N.S.), P‐value <0.01(**).

Figure 3

Grain filling rate and gene expression profiles from developing seeds at different temperatures. (a) Grain filling rate of RNAi line M734 and WT (ZH11) under HT and control (RT) treatment conditions. (b–d) Related expression levels of GBSSI (Wx2), SBEI and SSSI to UBQ10 in developing seeds under HT and RT conditions. (e, f) Intensity of mature Wx transcript (Wx10) and splicing efficiency (Wx10/Wx2) of GBSSI in developing seeds from WT (ZH11) and M734 at HT.

Figure 4

Morphologic analysis of rice seeds from constitutively suppressed OsMADS7 lines. (a) spikelet fertility (n = 5), (b) seed width, (c) seed length and (d) seed weight (n ≥ 300) of suppression lines of OsMADS7 and WT (ZH11) under high temperature (HT) and control (RT) treatments. Data represent means ± SE. A significant difference was determined by Student's t‐test, P‐value <0.01(**).

Figure 5

Characterization of endosperm‐specific suppression lines of OsMADS7. (a) Relative expression of OsMADS7 in rice endosperm (9 DAP) in the suppression lines and WT (NIP). Transcripts were measured using qRT‐PCR and normalized to the level of WT control using UBQ10 as internal control. Data represent means ± SE, n = 3 biological replicates. (b) Rice AC of the suppression lines and WT at high temperature (HT) and room temperature (RT). (c) DD‐values of the suppression lines between the HT and RT conditions. (d) Spikelet fertility of suppression lines of OsMADS7 and WT under HT conditions. Data represent means ± SE, n = 5 biological replicates. A significant difference was determined by Student's t‐test, not significant (N.S.), P‐value <0.05(*), P‐value <0.01(**).