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 44

genes in pollen ( Hsu et al., 2007 ), almost half (15) exhibit high-average
hydrophilicity based on hydropathy profile analysis ( Kyte and Doolittle,
1982 ). The rest of proteins, however, should be protected by those osmo-
protective molecules to maintain their biological functions.
Shinozaki et al. (2003) classified the products of drought-inducible genes
into two groups. The first group includes proteins directly involved in plant
survival under stressful conditions. Several of the 34 desiccation-associated
proteins listed in Table 2.1 were classified into the first group after examina-
tion. For instance, various proteases, such as alpha/beta hydrolase (clone 19),
serine protease (clone 30), pectinesterase (clone 37), and pectate lyase (clone
52), may be involved in stress defense. The putative SF16 protein (clone
69) may be involved in the stability and maturation of pollen mRNAs
( Dudareva et al., 1994 ). LLA23 acts as a chaperone and a regulator upon
drying ( Yang et al., 2005 , 2008 ). The peroxidase ATP14a homolog (clone
21) and putative glutathione transporter (clone 28) may be involved in oxi-
dative detoxification. Moreover, several transporters, such as histidine amino
acid transporter (clone 54), monosaccharide transporter (clone 64), and
Isp4-like protein (clone 90), exist in the dried pollen for the transportation
of sugar and amino acids. The plasma membrane H + ATPase (clone 57) may
be associated with ion homoeostasis. In addition, the HVA22 homolog, an
LEA protein, is also included in this group, although it begins to accumulate
during the early maturation stage and continues to accumulate until the full
maturation of the anther ( Hsu et al., 2007 ).
The second group is composed of regulatory proteins that include tran-
scription factors and other signaling molecules, such as ATP-dependent Clp
protease regulatory subunit ClpX (clone 39), calcium-dependent protein
kinase (clone 50), serine/threonine protein phosphatase (clone 56), ring
zinc finger protein (clone 58), a retrotransposon protein (clone 71) and
LLA23 ( Table 2.1 ). Taken together, the division into two groups of drought-
inducible genes proposed by Shinozaki et al. (2003) may be applied to the
desiccation-associated genes in dried pollen as well.
3. ASR
3.1. Gene Expression and Organization of the Asr Genes
3.1.1. Distribution and Spatial and Temporal Expression
Asr is a stress-inducible gene that is reportedly exclusively to plants. Since
Iusem et al. (1993) described the first Asr gene from tomato, Asr genes have
been found in various species of dicotyledonous and monocotyledonous