小麦杂交种与亲本发育早期种子的基因表达差异及其与杂种优势关系的初步研究

为深入探讨小麦杂种优势形成的分子机理，选取3个冬小麦品种(系)为一组亲本，3个为另一组亲本，配制了正反交18个杂交组合，以授粉后6d的杂交和自交种子为材料，应用mRNA差异显示技术(DDRT—PCR)研究了小麦杂交当代种子与其亲本自交种子基因的表达差异，并与杂种优势进行相关分析。为降低DDRT—PCR技术假阳性的不利影响，对每个引物组合均作了两次PCR扩增，在处理数据时，仅统计能重复出现的条带。结果发现：杂交种和亲本之间的基因表达模式有8类共15种：(1)单亲沉默型(2种)，(2)单亲一致型(2种)，(3)正交或反交沉默型(2种)，(4)正交或反交特异型(2种)，(5)正交或反交单亲一致型(4种)，(6)杂交种特异型(1种)，(7)双亲共沉默型(1种)，(8)表达一致型(1种)。分析发现，小麦杂交种和亲本间存在显著的表达差异。在差异表达类型中，杂交种特异型和双亲共沉默型比例最低。对上述15种表达模式与杂种优势进行相关分析，结果表明，表达一致型与各产量性状杂种优势之间的相关均不显著，说明杂种优势是由某些有表达差异的基因造成。9个产量性状均能检测到一种以上与其显著或极显著相关的基因表达模式，有些性状受正负相关效应的共同影响；沉默型(包括单亲沉默型、正交或反交沉默型和双亲共沉默型)和正交或反交单亲一致型在杂种优势形成中发挥重要作用。这些研究表明，在种子发育早期，基因的差异表达与杂种优势形成之间可能存在较为复杂的关系。

Relationship between Differences of Gene Expression in Early Developing Seeds of Hybrid versus Parents and Heterosis in Wheat

In order to understand molecular basis of heterosis,mRNA differential display was used to analyze the differences in gene expression between seeds of 18 reciprocal hybrids and their 6 parents at 6th day after pollination.The relationship between gene expression patterns and heterosis was determined.Only bands that can be repeated in duplicate PCR were used for analysis so as to reduce false positive bands.Among the total of 2 025 bands displayed,1 386 bands (68.43%) were reproducible.Eight patterns (fifteen kinds) of gene expression were observed,which include:(1) bands occurring in only one parent (two kinds);(2) bands observed in both hybrids and one parent (two kinds);(3) bands detected in parents and one hybrid (two kinds);(4) bands displayed in only one hybrid (two kinds);(5) bands revealed in one hybrid and its corresponding female (two kinds) or male(two kinds) parent;(6) bands visualized in only both hybrids (one kind);(7) bands occurring in only parents (one kind);(8) bands observed in parents and both hybrids (one kind).Our results indicate that differences of gene expression between hybrids and their parents are very obvious.The percentages of bands observed in only both hybrids and in only both parents are lower.The analysis shows that bands observed in parents and both hybrids are not correlated with all nine agronomic traits,which indicates differentially expressed genes are mainly responsible for the observed heterosis.At least one pattern of differential gene expression is significantly correlated with nine agronomic traits.Silenced bands in hybrid (which include bands occurring in only one parent,bands detected in both parents and one hybrid and bands in only parents) and bands present in one hybrid and its corresponding female or male parent are likely to play important roles in heterosis.These results suggest that early seed development could be closely related to heterosis.