New Insights into Desiccation-Associated Gene Regulation by Lilium longiflorum ASR during Pollen Maturation and in Transgenic Arabidopsis - International Review of Cell and Molecular Biology - page 38

withstands drying during maturation becomes desiccation tolerant. Such
pollen was recently termed “orthodox” by Pacini et al. (2006) . The con-
cept of orthodox pollen is opposed to so-called recalcitrant pollen, which
is highly susceptible to desiccation damage because it does not undergo
maturation drying and is shed with relatively high moisture content ( Fran-
chi et al., 2011 ). To ensure the survival of orthodox pollen in unfavorable
environments, mechanisms associated with desiccation tolerance involve
an array of metabolic shutoff genes during developmental arrest and the
expression of new genes that encode protective molecules under desiccated
conditions ( Franchi et al., 2011 ). A sizable number of protective molecules,
such as proline, sucrose, oligosaccharides, and amphipathic molecules, have
been identified in desiccated pollen ( Lehmann et al., 2010 ; Pacini et al.,
2006 ; Schwacke et al., 1999 ). In particular, the well-known dehydrins, a
type of late embryogenesis abundant (LEA) proteins initially identified in
seeds, were detected in mature pollen grains ( Mogami et al., 2002 ; Wolkers
et al., 2001 ). LEA acts as an osmoprotectant that possesses chaperone-like
properties to protect enzymatic activity and prevent protein aggregation
resulting from water deficiency ( Goyal et al., 2005 ; Reyes et al., 2005 ). The
pollen LLA23 (a lily ASR) protein has also been found only in the matura-
tion drying stage ( Huang et al., 2000 ; Wang et al., 1996 , 1998 ). Although
LLA23 is pollen-specific, the organ or tissue specificity of ASR proteins is
diverse in other plant species ( Cakir et al., 2003 ; Liu et al., 2010 ).
2. DESICCATION-ASSOCIATED ABSCISIC ACID (ABA)
SIGNALING IN POLLEN GRAINS
2.1. Gene Expression Profiles during Pollen Maturation
Four studies reported the functional classification of transcripts and proteins
found in Arabidopsis pollen using a GeneChip array and proteomic analysis
( Becker et al., 2003 ; Holmes-Davis et al., 2005 ; Honys and Twell, 2003 ; Pina
et al., 2005 ). These studies provide valuable insights into the complexity
of gene expression in mature pollen. The occurrence of various growing
stages is supported by a number of earlier studies that indicated the presence
of different phases of RNA/protein synthesis during pollen development
( Schrauwen et al., 1990 ). However, information regarding the association of
gene expression with maturation drying is rather limited.
To characterize the gene expression profiles at the phase of matura-
tion drying, a subtractive cDNA library was prepared to identify the genes
associated with desiccation during anther development ( Hsu et al., 2007 ).